Novel Developments in Correlated Quantum Materials

In strongly correlated systems, exotic behavior emerges from the interaction between particles and the related competing energy scales. As a consequence, to describe them we need to go beyond single-particle approximations, which requires nontrivial analyses and the development of new experimental and theoretical techniques.

In this workshop, we will bring together young as well as prominent experimentalists and theoreticians to discuss emergent behavior, such as unconventional superconductivity, exotic quantum orders, and nontrivial topological phases.

We expect a rich exchange of ideas during the workshop and the possible establishment of new collaborations between the attendees.

Participants are invited to submit their works for the poster session. Prizes will be awarded to the 3 best contributions presented in this poster section – these prizes are sponsored by EPL (Europhysics Letters, https://www.epletters.net/). A few contributed works may be considered for oral presentations.

 

The workshop will be preceded by a school on a related topic: “School on Recent Advances in Strongly Correlated Quantum Materials” (ICTP-SAIFR, October 5-9, 2026).

 

• Helena Bragança (Universidade de Brasília, Brazil)
• Leni Bascones (Instituto de Ciencia de Materiales de Madrid, Spain)
• Maria Carolina de Oliveira Aguiar (Universidade Federal de Minas Gerais, Brazil)
• Ricardo Lobo (CNRS, École supérieure de physique et de chimie industrielles de la ville de Paris, France)

 

 

Announcement:

Application is now closed

Speakers

• Adrian E. Feiguin (Northeastern University, USA)
• Alberto Camjayi (Universidad Buenos Aires y Conycet, Argentina)
• Aleksandra Krajewska (Max Planck Institute: Stuttgart, Germany)
• Ana Akrap (University of Zagreb, Croatia)
• Andrés Santander (Université Paris-Saclay, France)
• Anna Tamai (University of Geneva, Switzerland)
• Artem Pronin (University of Stuttgart, Germany)
• Cristiane de Morais Smith (Utrecht University, Netherlands)
• David Santos-Cottin (University of Fribourg, Switzerland)
• Edson Vernek (UFU, Brazil)
• Eduardo Granado (UNICAMP, Brazil)
• Eduardo Miranda (UNICAMP, Brazil)
• José Hoyos (USP-São Carlos, Brazil)
• Krissia Zawadzki (USP-São Carlos, Brazil)
• Laura Fanfarillo (Institute of Complex Systems, Italy)
• Luca de’ Medici (ESPCI-PSL, France)
• Marcello Civelli (Université Paris-Saclay, France)
• Matthieu LeTacon (Karlsruhe Institute of Technology, Germany)
• Paula Giraldo (Universidad de los Andes, Colombia)
• Paula Mellado (Universidad Adolfo Ibáñez, Chile)
• Rodrigo Pereira (IIP & UFRN, Brazil)
• Simone Fratini (Institut Néel, France)
• Thaís Trevisan (USP-São Carlos, Brazil)
• Thereza Paiva (UFRJ, Brazil)
• Vidya Madhavan (University of Illinois, USA)

 

Announcement:

Application is now closed

 

 

Schedule

2026-10-12

• 09:00 - Artem Pronin (University of Stuttgart): Electrodynamics of electronic topological phases probed by far-infrared spectroscopy
• 09:40 - Edson Vernek (UFU): Stability of topological phases in Kitaev-Heisenberg ladders under charge fluctuations
• 10:50 - Thereza Paiva (UFRJ): Flat band and topological phases in a Fermi-Hubbard ladder
• 14:00 - Adrian E. Feiguin (Northeastern University): Hund excitons and singlet polarons in two-dimensional van der Waals magnets
• 14:40 - Thaís Victa Trevisan (USP): Pathways for controlling topological hinge states

2026-10-13

• 09:00 - Ana Akrap (University of Zagreb): Coupling of spin, lattice and charge degrees of freedom in a magnetic semiconductor, EuCd2As2
• 09:40 - David Santos-Cottin (University of Fribourg): From Optical Response to Landau Levels: Spectroscopy of Topological Materials
• 10:50 - Marcello Civelli (Université Paris-Saclay): Superconductivity-enhanced magnetism at a correlated cuprate–manganite interface
• 14:00 - Vidya Madhavan (University of Illinois): STM Measurements of Topology and Order Parameter in the Triplet Superconductor UTe2
• 14:40 - Aleksandra Krajewska (Max Planck Institute: Stuttgart): Materials aspects of superconducting candidate La3Ni2O7

1^st POSTER SESSION

Monday, October 12

1

• Andrade, Pedro Lucas C. (Universidade Estadual do Maranhão, Brazil): Magnon Propagation and Topological Phases in Hybrid Breathing-Honeycomb Lattice

Topological phases in quantum materials are commonly associated with electronic systems, but analogous phenomena can also emerge in bosonic collective excitations such as magnons. In this work, we investigate theoretically the magnon spectrum of a two-dimensional ferromagnetic lattice with exchange and Dzyaloshinskii–Moriya interactions, focusing on the emergence of nontrivial topological magnon bands. Starting from an effective spin Hamiltonian including exchange interactions, magnetic anisotropy, an external magnetic field and Dzyaloshinskii–Moriya terms, we apply bosonic spin-wave formalisms to obtain the quadratic magnon Hamiltonian in reciprocal space. The resulting band structure is analyzed numerically, with particular attention to gap openings, Berry curvature and Chern numbers. Our results indicate that Dzyaloshinskii–Moriya interactions can induce topological gaps in the magnon spectrum and generate nontrivial Berry curvature distributions in momentum space. These findings contribute to the broader understanding of how topology and collective magnetic excitations can coexist in low-dimensional quantum magnetic systems.

2

• Araujo Paiva, Gean Carlos (Instituto de Física, Universidade Federal do Rio de Janeiro, Brazil): Strong correlation in de dice lattice

Flat-band systems provide an ideal platform for investigating strong electronic correlations. When a flat band lies at the Fermi level, the suppression of kinetic energy enhances interaction effects, allowing ordered states to emerge even at arbitrarily weak coupling. A paradigmatic example is the dice lattice, whose energy spectrum features a zero-energy flat band touching two linearly dispersive Dirac cones at half filling. Although recent studies have explored dice-lattice ribbons, topological phases, and potential materials candidates—such as the electride $\mathrm{YCl}$—the combined effects of strong correlations and dice-lattice geometry remain largely unexplored. In this work, we investigate the finite-temperature magnetic and electronic properties of the repulsive Hubbard model on the dice lattice at half filling, taking advantage of particle-hole symmetry ($\mu=0$). Using unbiased determinant quantum Monte Carlo (DQMC) simulations, we evaluate spin-spin correlation functions, the electronic compressibility, and magnetic structure factors. Our results show that arbitrarily weak repulsive interactions induce strong ferrimagnetic correlations, accompanied by a suppression of electronic compressibility characteristic of an insulating state. The finite-size scaling and low-temperature behavior support a ferrimagnetic insulating ground state for any $U>0$. Furthermore, we examine the effect of spatially anisotropic hopping amplitudes, demonstrating how this tuning mechanism modulates correlation strength and alters the corresponding spin and charge responses. These findings establish the dice lattice as a robust platform for interaction-driven ferrimagnetism arising from the interplay between flat-band physics and sublattice imbalance.

3

• Arriagada Cortés, Christopher Andre (Universidad Técnica Federico Santa María, Chile): Higher-Chern Phases and Vorticity Constraints in Extended BHZ-Type Models

We study higher-Chern phases in extended BHZ-type two-band models on a square lattice. Starting from a spinless tight-binding Hamiltonian with (s)- and (p)-orbital degrees of freedom, we include symmetry-allowed further-neighbor hopping processes and analyze how these terms modify the topological structure of the Bloch Hamiltonian. The interorbital hybridization controls the number and position of Dirac points in the Brillouin zone, while the mass sector determines the corresponding band inversions and topological phase transitions. By expanding the Hamiltonian near the zeros of the interorbital hybridization, each gap-closing point can be described by an effective massive Dirac Hamiltonian. This allows the Chern number to be computed from a discrete sum over Dirac points, where each contribution is determined by the product of the local vorticity and the sign of the mass term. We show that increasing the hopping range generates additional Dirac points and enables phases with increasingly large Chern numbers. However, the maximum attainable Chern number is constrained by compatibility conditions among the mass signs, so that the naive bound obtained from vortex counting cannot always be saturated. Applying this construction up to sixth-neighbor hopping, we find higher-Chern insulating phases with Chern numbers as large as |C|=12. These results provide a systematic route to engineer high-Chern phases in extended BHZ-type lattice models and clarify the role of vorticity and mass inversion in determining their topology.

4

• Barboza, Pedro Loureiro (Instituto de Física da Universidade de São Paulo, Brazil): Homogeneous and inhomogeneous strain in the XY model in the triangular lattice

In this work, we investigate the classical XY model on the triangular lattice with the symmetry-allowed 6-state clock anisotropy and strain. We first examine the role of this clock anisotropy in the model’s low-temperature behavior, with particular attention to the emerging critical phases. We then model uniaxial stress as a competing 2-state clock anisotropy. The competition between two-fold and six-fold anisotropies leads to a phase diagram with paramagnetic, two-fold-ordered, and four-fold-ordered phases, separated by Ising critical lines that indicate the destruction of the critical phase. We also investigate random strain, introduced through inhomogeneous spatial distortions of the triangular lattice, which could, for instance, originate from defects in the substrate. Together, competing anisotropies and structural disorder provide a controlled setting for assessing the Berezinskii-Kosterlitz-Thouless physics under realistic perturbations. Our results contribute to understanding how inhomogeneities and competing symmetry-breaking fields reshape phase transitions in frustrated two-dimensional systems.

5

• Bento Da Silva, Daniel (instituto de física da universidade de São Paulo, Brazil): Dark solids in BEC on spherical shell with LHY interaction

In recent work by the group, the stability of dark solitons in Bose-Einstein condensates confined to a spherical shell was investigated. We establish the stability criteria for dark solitons on a spherical Bose-Einstein condensate. In previous works, it was demonstrated a sharp instability threshold in the nonlinear parameter, beyond which solitons decay into vortex dipoles via snake instabilities. Numerically, it was proved that decay is dictated by a single unstable mode for each angular momentum m ≥ 2, which is a universal mechanism that controls the resulting vortex state. In this project, we aim to conduct studies using this same geometry but employing the Lee-Huang-Yang interaction.

6

• Berber, Luigi Laurenti (Instituto de Física-UnB, Brazil): Many-Body Localization on Spin Chains

Many-Body Localization (MBL) offers a robust framework for understanding how isolated quantum systems can avoid thermalization in the presence of strong disorder. In this work, we investigate the out-of-equilibrium dynamics of strongly correlated spin-1/2 chains undergoing finite-time quantum quenches. Utilizing exact diagonalization and computational spin dynamics simulations, we track the time evolution of entanglement entropy and local observables to probe the ergodic-to-MBL phase transition. Our numerical results characterize how disorder inhibits transport and preserves local memory of the initial state, challenging standard statistical mechanics. This study highlights the interplay between interactions, disorder, and quantum coherence, driving forward our understanding of thermalization boundaries in quantum materials.

7

• Boscolo, Mariana De Jesus (IFSC USP, Brazil): Fractal dispersion in one-dimensional models and its topological characterization: Hofstadter’s Butterfly in 1D.

This work presents a study of the generalized one-dimensional Aubry-André-Harper (AAH) model featuring a periodic modulation of the spin-orbit coupling parameter. The interplay between the length scales associated with the modulation and the lattice spacing gives rise to physics similar to that of electrons in a square lattice subjected to an external uniform transverse magnetic field. Here, we explore the similarities between these two models, demonstrating, for instance, the emergence of a fractal spectrum similar to the Hofstadter butterfly. The AAH model supports phases with non-trivial topology. We investigate the dependence of the fractal spectrum on the parameters of the model and provide a topological characterization of the energy gaps within the fractal spectrum.

8

• Cardenas Castillo, Luis Fernando (Pontificia Universidade Católica do Río de Janeiro, Brazil): Optical pulse-induced quantum geometric waves in graphene

We show that, under a short optical pulse, the quantum metric of Bloch states in the momentum-time (kx, ky, t) of graphene becomes dynamic and exhibits a wave-like behavior near Dirac points. This quantum metric wave reflects the Floquet-band structure caused by the pulse, as revealed by solving the time-dependent Schrödinger equation assuming that correlations and out-of-equilibrium effects can be ignored. The momentum and temporal components of the metric have very distinct time dependence that persists even after the pulse has passed. In addition, the pulse also generates a Berry curvature wave that is otherwise absent in static graphene. The time-dependent electron densities in conduction and valence bands also give arise to a Fisher information wave that constitutes part of the quantum metric wave, and is readily measurable by pump-probe experiments.

9

• Costa, Danielle Parente Da (Instituto de Física, Universidade de Brasília, Brazil): One-Dimensional Extended Hubbard Model in Equilibrium and Out of Equilibrium

Strongly correlated one-dimensional systems can be described by the Extended Hubbard Model, which captures the competition between kinetic and interaction energies through the parameters U, V and t. Motivated by recent interest in the regime U > 0 and V < 0 (local Coulomb repulsion and attractive nearest-neighbor interaction), relevant to cuprate chains, we investigate the model using the Density Matrix Renormalization Group (DMRG) in its Matrix Product State (MPS) formulation, both in equilibrium and out of equilibrium. In equilibrium, we identify superconducting phases and phase-separated regions (PS1, PS2, and PSx), with singlet and triplet pairing correlations consistent with previous studies. To investigate the nonequilibrium dynamics, we consider a phase-separated state (PS2) at quarter filling and perform both sudden and slow quenches of V within the fourth quadrant while keeping U fixed. The resulting dynamics exhibits particle propagation throughout the chain, accompanied by the growth and spatial spreading of entanglement entropy and the emergence of superconducting correlations. In all cases, the system relaxes toward the occupation profile of the ground state corresponding to the final value of V. Ongoing work focuses on a detailed analysis of the nonequilibrium dynamics, including the behavior of the measured observables and the dependence of the system response on the quench rate.

10

• De Figueiredo, Guilherme Fragoso (UNICAMP, Brazil): The $J_1$-$J_2$ antiferromagnet Heisenberg model with a Dzyaloshinskii-Moriya interaction in a honeycomb lattice: valence-bond solid phase and thermal Hall conductivity

We study the topological properties of a columnar valence-bond solid phase in a honeycomb lattice,in particular, we calculate the thermal Hall conductivity $\kappa_{xy}$ due to the elementary (triplon) excitations of this quantum paramagnetic phase. We consider a honeycomb lattice spin-$1/2$ $J_1$-$J_2$ antiferromagnetic Heisenberg model with an on-site anisotropy between the sites of the two triangular sublattices and in the presence of a Dzyaloshinskii-Moriya interaction between nearest-neighbor spins and an external magnetic field. Two (in-plane) Dzyaloshinskii-Moriya vector patterns are considered, both allowed by the symmetries of a honeycomb lattice with two distinct sites per unit cell. The columnar valence-bond solid phase is described within the bond-operator representation for the spin operators, a formalism that allows us to map the original Heisenberg model into an effective interacting boson model expressed in terms of triplet operators. We consider the effective boson model within the harmonic approximation and determine the region of stability of the valence-bond solid phase and triplon excitation bands. Moreover, the Berry curvatures and the Chern numbers of the triplon excitation bands are determined, as well as the temperature dependence of the thermal Hall conductivity due to triplons. Similar to a previous study concerning a square lattice columnar valence-bond solid [Phys. Rev. B 109, 134405 (2024)], we find that a Dzyaloshinskii-Moriya interaction indeed provides a finite Berry curvature for the triplon bands, but, in spite of that, the Chern numbers of the triplon bands vanish, yielding a phase characterized by topologically trivial elementary excitations; interestingly, the thermal Hall conductivity $\kappa_{xy}$ due to triplons is finite at low temperatures. Such a feature corroborates our previous findings concerning the square lattice columnar valence-bond solid that indicated that the no-go condition for a thermal Hall effect [Phys. Rev. Lett. 104, 066403 (2010)], previously determined for ordered magnets, might not be valid for a valence-bond solid phase.

11

• De Souza, Guilherme Antônio (Universidade Estadual de Campinas – UNICAMP, Brazil): Spectral fingerprints in relaxation and quantum work statistics of a boundary-controlled XX chain

Understanding how local spectral features govern nonequilibrium response is relevant for the characterization and control of quantum systems, especially when impurities, interfaces, or edges support modes not captured by a bulk description. We investigate this connection in an XX spin chain with a tunable boundary impurity. Depending on the boundary field, the local spectrum contains a continuum of extended states and may also host a localized boundary mode, with distinct regimes separated by spectral thresholds. We examine how this structure is reflected in the relaxation of a local observable after a boundary perturbation and in the associated quantum work distribution, which characterizes the energy fluctuations generated by the process. Although relaxation and work statistics probe the dynamics in different domains, both are organized by the same spectral ingredients. Changes in the continuum, its band edges, and the presence or proximity of the localized mode reorganize the long-time relaxation and produce characteristic features in the work distribution. Our results therefore establish relaxation and work statistics as complementary time- and energy-domain probes of boundary spectral structure, unifying recent perspectives on impurity relaxation and edge-state signatures in quantum work statistics. This connection provides a coherent framework for identifying how boundary modes influence nonequilibrium quantum thermodynamics.

12

• Dos Santos, Edine Silva (Centro Brasileiro de Pesquisas Físicas, Brazil): Dehybridization transition in multi-band systems

In strongly correlated multi-band systems, such as intermetallics, heavy fermions, and Kondo insulators, electron-electron interactions lead to the damping of electronic quasiparticles at finite temperatures. This phenomenon results in an effective dehybridization between the electrons in the large conduction band and those in the narrow, correlated band. The dehybridization effect has been employed to explain the temperature dependence of several physical properties of intermetallics, heavy fermions and actinide compounds. Recent insights from the theory of non-Hermitian systems provide a novel perspective on this problem. We adopt this viewpoint through a renormalization group (RG) approach. We derive RG equations for a one-dimensional two-band model to identify the exceptional points of this system and to characterize its topological properties. Our findings reveal that for a topological, non-Hermitian particle-hole-symmetric chain, dehybridization can be interpreted as a topological phase transition, characterized by critical exponents that we calculate. We discuss the nature of the energy scale for dehybridization in the context of the phase diagram of heavy fermions.

13

• Faundez, Julian (Universidad Andres Bello, Chile): Superconducting, charge-density-wave, and topological phases in the spin-orbit-coupled Kagome-Holstein model at Dirac filling

We investigate the interplay between topology and electron-phonon interaction on a Kagome lattice by considering a spin-orbit-coupled-Holstein model at Dirac filling. We find that the Kane-Mele type spin-orbit coupling realizes a quantum spin Hall insulator for weak \textit{e-ph} interactions. Using determinant quantum Monte Carlo, we establish that increasing the Holstein interaction destroys topology, and the system undergoes a transition from a charge density wave phase at low phonon frequencies to a superconducting state at larger frequencies. At low frequencies, the topological transition is probed by a many-body Bott index, while a local topological marker is used at higher frequencies. By employing finite-size scaling of the charge and pairing correlation functions and spectral and open-boundary analyses, we map out the complete phase diagram of the system.

14

• Felix, Felipe Martins (Universidade Estadual de Campinas, Brazil): Electronic and magnetic properties of S-graphene compound

The experimental discovery of two-dimensional crystalline structures, such as graphene, has stimulated research due to their potential applications in several fields. The literature has reported stable carbon allotropes, such as S-graphene (SG), that exhibit Dirac cones. Additionally, a notable characteristic of S-graphene is the possibility of opening a gap at the Fermi level under lattice deformations. Motivated by these results, in this work we analyze the electronic and magnetic responses of the SG under structural deformations induced by strain using the Hubbard model. As a result, for the non-interacting case, this carbon allotrope can behave as (i) a band insulator, (ii) a Dirac semimetal, or (iii) a flat band insulator. We examine the interacting case using two different methodologies: mean-field theory and quantum Monte Carlo simulations, to determine the phase diagram of the model as a function of the strain and the electron-electron interaction. Interestingly, we notice the presence of semimetal, band insulator, and antiferromagnetic insulator states. Motivated by these results, we also perform first-principles calculations via Density Functional Theory (DFT), which indicate the presence of a spin-polarized phase as the lowest-energy state. The spatial distribution of the magnetization reveals that the central sites of the SG lattice are primarily responsible for the observed magnetic behavior. The theoretical predictions based on mean-field theory and DFT corroborate each other, demonstrating that applying strain to the SG structure plays a fundamental role in modulating its electronic and magnetic properties.

15

• Gama D’Elia, João Pedro (Universidade Federal do Rio de Janeiro, Brazil): Multiple Topological Haldane Phases for Symmetry-Protected Quantum Information Processing

Symmetry-protected topological phases have attracted significant interest at the fundamental level and as a potential platform for quantum information processing, owing to their protected edge states and resilience to perturbations. Applying these features for practical and efficient quantum computation is highly desirable, but remains an open challenge. Here, we demonstrate the partitioning into multiple independent Haldane phase subsystems of a single spin-1/2 ladder system and propose this as a scalable architecture for gate-based quantum computation, which takes advantage of the symmetry-protected topological order. We encode qubits in the two topological states of the Sz =0 sector of each subsystem. Finite-size effects, typically viewed as detrimental, instead provide a controllable energy splitting that enables single-qubit rotations using only local magnetic fields. An Ising-type interaction between neighboring subsystem edges generates entangling gates, enabling universal quantum computation driven by two control parameters that are easily accessible experimentally. Our results demonstrate how symmetry-protected topological phases can be directly harnessed for circuit-model quantum computation in realistic systems.

16

• Ghosh, Debankita (Pontificia universidad catolica de chile, Chile): Orbital anisotropy and anomalous Hall conductivity in SrRuO₃ under uniaxial strain

The itinerant ferromagnet SrRuO₃, a 4d transition-metal oxide with strong spin-orbit coupling, has emerged as a canonical platform for exploring the interplay between structural distortion, orbital physics and Berry-phase-driven transport phenomena. Despite extensive studies of SrRuO₃ under symmetric biaxial epitaxial strain, the consequences of directionally selective, symmetry-breaking uniaxial deformation on its orbital, magnetic and topological properties remain poorly understood. Here, we report a systematic first-principles investigation of SrRuO₃ under uniaxial strain applied along the crystallographic b-axis (−0.6% to +0.6%), with the a- and c-axis parameters held fixed, using density functional theory with a Hubbard correction (DFT+U, U = 2.0 eV, J = 0.6 eV) as implemented in VASP. Our findings demonstrate that uniaxial b-strain induces a fundamentally anisotropic structural perturbation within the RuO₆ octahedra, resulting from a competitive interplay between tilt-induced bandwidth narrowing and the redistribution of orbital weight. This uniaxial strain selectively lifts the near-degeneracy of the , , and orbitals, governed by the oxygen sublattice via the Ru-O bonding channel. Although the overall band structure exhibits stability across the investigated strain range, orbital-resolved density of states and charge density difference maps indicate a directionally anisotropic charge redistribution. This effect drives a non-monotonic modulation of the intrinsic anomalous Hall conductivity (AHC), calculated using the Kubo-Berry curvature formalism. These results establish a direct microscopic pathway where uniaxial strain induces 2 orbital anisotropy, which in turn modulates the Berry curvature and the resulting AHC. Consequently, symmetry-breaking uniaxial strain emerges as a powerful tool for engineering Hall conductivity in correlated 4d oxide ferromagnets.

17

• Gonçalves, Pedro Henrique Rezende (UFMG, Brazil): Metallic layered materials with magnetic frustration: An ARPES study

Compounds of the LnTAl4X2 (Ln = lanthanide, X = tetrel, T = transition metal) family has attract significant scientific interest due to their geometrically frustrated triangular lattices, rising into exotic magnetic phenomena such as complex spin arrangements and multiple magnetic transitions [1-2]. Despite the significant report on their magnetotransport properties, their experimental electronic structure had remained largely unexplored [3-4]. In this work, we present a detailed investigation of the electronic structure of SmAuAl4Ge2 and TbAuAl4Ge2 using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. Our results show that both compounds possess a highly two-dimensional Fermi surface characterized by multiple hole pockets around the Γ-point. We demonstrate that the main features of the electronic structure are well-captured by the nonmagnetic analog YAuAl4Ge2, providing experimental confirmation of negligible hybridization between the f-electrons and the conduction states. Despite this weak direct interaction, we find that the localized magnetic moments of the f-electrons exert a crucial indirect influence. Specifically, the exchange interaction combined with spin-orbit coupling leads to a fine energy splitting of the bands near the Fermi level, a feature that is absent in the nonmagnetic analog. Additionally, we identify the presence of surface-localized electronic states and determine the dominant cleavage plane of the materials. Although the materials undergo magnetic transitions at low temperatures, no significant changes in the electronic structure were observed across these transitions within our experimental resolution. This study concludes that low-dimensionality, surface termination, and exchange interactions are fundamental ingredients in defining the electronic properties of these frustrated magnetic systems. [1] G. H. Wannier, Phys. Rev. 79, 357 (1950). [2] M. A. Ruderman and C. Kittel, Phys. Rev. 96, 99 (1954). [3] K. Feng et al., Phys. Rev. B 109, 014436 (2024). [4] K. Feng et al., J. Magn. Magn. Mater. 564, 170006 (2022).

18

• Guedes, Silas Michael Batista (University of São Paulo, Brazil): Impurities and vacancies in Twisted Bilayer Graphene

Twisted bilayer graphene (TBG) has become a particularly relevant system in recent years due to the electronic properties observed in the magic-angle regime. Furthermore, previous studies have shown interesting long-range effects and modifications of the band structure when a single defect is introduced in TBG. Using an atomistic tight-binding model, we study the effects of impurities and single vacancies on the band structure and the density of states (DOS) of TBG at a twist angle of 4.4°. Our results show a split in a pair of moiré bands — whose separation is determined by the defect strength — and the appearance of small peaks in the DOS. We further relate these results to the already-known band restructuring process and show that TBG at 4.4° exhibits effects that anticipate those in the magic-angle regime.

19

• Marino, Vito (SISSA, Italy): Influence of the inter-orbital interaction and kinetic terms on superconductivity: a simple two-orbital Hubbard model

A minimal two-orbital Hubbard model with nearest-neighbor hopping and no Hund’s coupling is investigated when the electron density is reduced from half filling (n = 2). To focus on the elec- tronic mechanisms of superconductivity, we restrict the variational ansatz to paramagnetic states and compute pairing correlations on top of optimized Jastrow-Slater wave functions. Here, super- conducting correlations are highly enhanced by the presence of inter-orbital terms, such as on-site Coulomb repulsion U ′ and nearest-neighbor hopping ˜t. When considering ˜t = 0, a finite value of U ′ effectively screens the intra-orbital repulsion U , producing a shift in the superconducting dome. Consequently, at moderately large values of U , inter-orbital repulsion yields a sizable increase in electron pairing compared to the single-orbital baseline. Furthermore, introducing a finite ˜t provides an additional boost to superconducting correlations, an effect driven by the simultaneous presence of flat and dispersive bands in the electronic structure.

 

2^nd POSTER SESSION

Wednesday, October 14

1

• Hernandez Cepeda, Nohora Alejandra (Ohio University, United States): Morphing polaron cloud near frustrated interfaces in Nagaoka ladders

The search for kinetic magnetism in strongly interacting systems has recaptured the attention of the quantum community, given the advances in the Hubbard model simulation in experimental platforms like cold atoms and moiré materials. As Nagaoka stated, a ferromagnetic ground state emerges in a square lattice when the system is doped away from half-filling, in the limit of infinite interactions. However, if a diagonal hopping (t’) is added to the square lattice, this ferromagnetic (FM) state becomes unstable as t’ takes over, giving rise to an antiferromagnetic (AFM) state. In this work, we investigate the presence of an interface where an abrupt change from non-frustrated to frustrated hoppings exists in a ladder geometry. By performing density matrix renormalization group (DRMG) simulations, we find that FM clouds (Nagaoka polarons) decay as t increases but without signs of spin-spiral behavior. At t’n/t > 0.75 the system transitions to a striped phase where the polaron exhibits AFM order. Finally, we find that the nature of the magnetic correlations can be tracked by following the hole propagation in the ladder: a FM (AFM) polaron corresponds to a delocalized hole in the square (triangular) part of the ladder. This demonstrates that the hole propagation is essential for polaron formation, and that the presence of an interface delocalizes it asymmetrically, determining the magnetic character of the ground state polaron.

2

• Jofré Parra, Fabián (Pontificia Universidad Católica de Chile, Chile): Electron-phonon interactions and instabilities in Weyl semimetals under magnetic fields and torsional strain

We study the presence of an external magnetic field, in combination with torsional strain, over the electron-phonon interactions in a type I Weyl semimetal. This particular superposition of field and strain, modeled in the continuum approximation by an effective gauge field, leads to an asymmetric pseudomagnetic field at each Weyl node of opposite chirality. Therefore, we also studied the role of nodal asymmetry in the properties of the system by means of the Kadanoff-Wilson renormalization group and the corresponding flow equations. By solving those, we discuss the evolution of the coupling parameters of the theory, and we analyze possible fixed points and lattice (Peierls) instabilities emerging from interactions between phonons with the chiral Landau level in the very strong pseudomagnetic field regime.

3

• Khairnar, Gaurav Ramesh (Instituto de Física, Universidade de São Paulo, São Paulo, Brazil, India): Non-ergodic states in aperiodic quantum chains

The spin-1/2 XXZ chain under strong aperiodic modulation hosts a localized low-energy phase driven by emergent dimerization of renormalized couplings. Whether non-ergodicity persists across the full many-body spectrum remains an open question. In this work, we address this question using exact diagonalization of chains with up to L=20 sites in the zero-magnetization sector. We characterize eigenstates over the full energy spectrum through the level-spacing ratio, properties of local observables, and bipartite entanglement entropy. We find that eigenstates exhibit clear signatures of non-ergodicity across all energy densities: the level statistics deviate from the Wigner-Dyson distribution expected for thermalizing systems under the eigenstate thermalization hypothesis (ETH), local observables violate ETH, and the bipartite entanglement entropy exhibits sub-volume-law scaling. Our results suggest that the aperiodicity-induced dimerization stabilizes non-ergodic behavior across the many-body spectrum, offering new insight into the interplay between deterministic aperiodicity, quantum entanglement, and ergodicity breaking.

4

• Manya Suni, Marco Antonio (Universidad Federal Fluminense (UFF), Brazil): Freezing scars

We study the dissipative dynamics of two collective spin ensembles, $A$ and $B$, each formed by $N_\alpha$ spin-$1/2$ particles restricted to the fully symmetric (Dicke) subspace $S_\alpha = N_\alpha/2$, with $\alpha = A/B$. The ensembles are coupled to a common environment through the collective jump operator $L \propto \left(S_-^{(A)} + S_-^{(B)}\right) $ and evolve under the coherent Hamiltonian $H_{\mathrm{ev}}$. Using the quantum-trajectory (Monte Carlo wave-function) method, we follow the quantum state in the coupled basis of total angular momentum $\lvert J, M \rangle$. The projected populations reveal sectors $(J,M)$ whose coefficients remain frozen in time despite the dissipation—a phenomenon we refer to as a \emph{freezing scar}. This is importante because freezing phenomena save the initial quantum information into a secto of subspace of same value of total angular momentum, it is studied to be apllied in quantum memory. We analyze this freezing as a function of the initial rotation angle $\theta_B$ and of the ratio $\omega_0/\kappa$, comparing the boundary-time-crystal regime ($\omega_0/\kappa = 1.3$) and the critical-point regime ($\omega_0/\kappa = 1.0$).

5

• Meira, Gabriel Menegolo De Castro (São Paulo State University (UNESP), Brazil): Strongly chiral dependence in the electronic scattering by impurities in multi-Weyl semimetals: a hybrid DFT-Anderson Hamiltonian based approach.

In this work, we investigate the signatures of Fano interference in multi-Weyl semimetals containing correlated impurities, through an approach that integrates first-principles calculations and analytical modeling. Employing Density Functional Theory (DFT) via Quantum ESPRESSO, a comparative analysis of the electronic properties of TaAs (single-Weyl, J = 1) and SrSi2 (double-Weyl, J = 2) was performed. The results revealed that the density of states of SrSi2 exhibits a pronounced slope (a “tilted plateau”) in the vicinity of the Fermi level, a phenomenon not predicted by canonical Weyl models. To describe this behavior, we introduced the concept of chiral weight (Ws), a dimensionless parameter associated with the axial velocity that modulates the spectral contribution of each chirality. Concurrently, an analytical model was developed based on the Green’s function formalism and the Anderson impurity Hamiltonian, from which closed-form expressions for the self-energy and the local density of states (LDOS) were derived. The total LDOS was decomposed into a pristine component and transmittance terms associated with intra- and inter-chiral scattering channels. The numerical results show that the broken inversion symmetry in Weyl semimetals introduces a chiral selectivity in the electronic coupling, resulting in the violation of the mirror symmetry of the resonance peaks, due to a “tilted parabola” and a “tilted plateau” in the pristine DOS for J = 1 and J = 2, respectively. For a majority positive chiral weight, the transmittance of the negative chirality channel (T−−) predominates for energies ε < 0, whereas the positive channel (T++) dominates for ε > 0. This asymmetry, absent in Dirac semimetals, constitutes the signature of the topological Fano effect and is directly related to the topological charge J and the chiral weight Ws.

6

• Narváez Burbano, Miguel Eduardo (Universidad del Valle, Colombia): Emergence of Majorana Zero Modes by Quantum Points in the Kitaev Chain

This project proposes the numerical analysis and characterization of the emergence of topologically protected edge states. Initially, an infinite Kitaev chain is considered, in which topological phases can occur. Through the variation of the local chemical potential of a set of sites with a determined distance, a boundary phenomenon is induced, proposing a continuous transition of the system from an infinite chain to a finite one as the chemical potential landscape is accentuated. The system parameters are chosen such that, in the finite chain, there are edge states with zero self-energy. The model will be solved using numerical methods, analyzing the behavior of the spectrum and tracking the states with zero or near-zero self-energy.

7

• Nascimento Oliveira, Luna Rhaine (UFPR, Brazil): Spin-dependent transport in long semiconductor heterostructures with Rashba effect: A Green’s function approach

The Rashba effect is a manifestation of spin–orbit coupling in systems with structural inversion asymmetry, resulting in a spin-dependent splitting of energy bands in low-dimensional systems. This gives rise to diverse spin-dependent phenomena in semiconductor heterostructures, offering significant potential for spintronic applications. However, a comprehensive theoretical characterization remains incomplete, since most existing approaches are restricted to relatively small structures. In this work, we combine the well established eight-band Kane model and envelope-function formalism with a recently developed Green’s function approach. The framework allows to obtain analytical expressions for the spin-dependent coherent transport 4in semiconductor heterostructures with an arbitrary number N of cells exhibiting the Rashba effect. In addition, we propose guidelines for enhancing spin polarization and spin-miniband separation in extended semiconductor heterostructures by tuning structural inversion asymmetry. Furthermore, we find that as a geometric parameter is varied, the spin-splitting dynamics present the quantum avoided-crossing behavior. We finally show that, for suitably designed heterostructures, the polarization bands can exhibit step-like (rectangular-wave) profiles. Although our examples focus on GaAs/In-based systems, the results are expected to hold for other semiconductor materials as well.

8

• Oliveira Santos, Julia (Universidade Federal de Minas Gerais, Brazil): Exploring phases of the two-dimensional Hubbard model: fitting the superconducting numerical solution to a phenomenological model.

Julia O. Santos,1 Vitor A. M. Lima,1,2 Helena Bragança,3 Maria C. O. Aguiar1 1 Departamento de Física, Universidade Federal de Minas Gerais, Brazil 2 Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, France 3 Instituto de Física and International Center for Physics, Universidade de Brasília, Brazil Materials with strong electronic interaction, such as copper oxides, exhibit phenomena that emerge from this interaction, one example of which is superconductivity. In addition to the superconducting phase, which origin is not well understood, there are other phases of these systems that are of interest, such as the pseudogap one, where there is a suppression of spectral weight in certain directions in momentum space. A model that describes correlated systems is the Hubbard model, which does not have an exact solution in two dimensions. In a previous work of our research group [1], the Hubbard model was numerically solved using Cellular Dynamical Mean Field Theory (CDMFT). Two distinct metallic phases were found at strong electronic interactions: the conventional Fermi liquid phase, at high dopings, and the pseudogap one, at small dopings, in accordance with the cuprate phase diagram. In this work, we obtain superconducting solutions from CDMFT in order to construct a phase diagram with superconductivity and to fit the numerical data to a phenomenological model [2], in which the low energy conducting electrons are described through the hybridization to hidden localized fermions. The advantage of the phenomenological model is that we can write down analytical expressions for the Green’s functions describing the different phases of the correlated system. By fitting our numerical data to these expressions, we obtain the model parameters, such as the hidden fermion energy and the hybridization to the conduction electrons, as a function of doping. In addition, we can “turn off” the superconducting order parameter in the analytical expressions and examine the normal phase corresponding to the superconducting one. This analysis of the numerical data based on a phenomenological model gives us insights about the relationship between the superconducting phase and the pseudogap one (obtained in our previous work). We acknowledge financial support from FAPEMIG, CNPq, and CAPES. References: [1] BRAGANÇA, Helena et al. Correlation-driven Lifshitz transition at the emergence of the pseudogap phase in the two-dimensional Hubbard model. Physical Review Letters, v. 120, n. 6, p. 067002, 2018. [2] SAKAI, Shiro; CIVELLI, Marcello; IMADA, Masatoshi. Hidden-fermion representation of self-energy in pseudogap and superconducting states of the two-dimensional Hubbard model. Physical Review B, v. 94, n. 11, p. 115130, 2016.

9

• Pereira Castro, Lucas Taylor (Universidade Federal de Minas Gerais (UFMG), Brazil): Comparative Study of the Transition to Quantum Chaos in the Transverse Field Ising Model

We perform a comparative numerical analysis of the integrability-to-chaos transition in the Transverse Field Ising Model (TFIM). Our main focus is on investigating how different mechanisms of integrability breaking affect thermalization in the TFIM, as a framework with significant relevance to experimental dipolar magnets such as LiHo_xY_{1-x}F_4. In these materials, the application of a transverse field can induce random longitudinal components due to the mixing of crystal field states, fundamentally altering the system’s dynamics. We simulate the model’s evolution under two distinct perturbations: (i) the addition of a next-nearest-neighbor (NNN) interaction (J2), which preserves spin-parity (Z2) symmetry, and (ii) the addition of a longitudinal field (hz), which explicitly breaks this symmetry. Using Exact Diagonalization (ED) for chains up to $L=18$, we investigate the emergence of chaos through multiple static and dynamical diagnostics. The static diagnostics include level spacing statistics, the level spacing ratio (), the Eigenstate Thermalization Hypothesis (ETH) and entanglement entropy. The dynamical diagnostics are the growth of Lanczos coefficients as a proxy for Krylov complexity and the Spectral Form Factor (SFF). Our results confirm that both perturbations induce chaos in intermediate regimes. However, the analysis reveals fundamental differences. While the chaos induced by NNN interactions is robust, the longitudinal field triggers a re-entrance into an integrable-like regime at strong fields. This re-entrant behavior is marked by the loss of spectral rigidity, the emergence of level bunching in the energy spectrum, and a fragmented Hilbert space that hinders complete thermalization. We conclude that the mechanism of integrability breaking, particularly the preservation or violation of the Z2 symmetry, fundamentally dictates the robustness of quantum chaos and the efficiency of the thermalization process, providing insights into the thermalization of correlated quantum materials.

10

• Picoli, Felipe Donizete (São Carlos Institute of Physics, University of São Paulo, Brazil): Real-Time Dynamics of the Interacting Resonant Level Model with real-space Numerical Renormalization Group

We investigate the real-time dynamics of the interacting resonant level model (IRLM), a paradigmatic quantum impurity model for studying transport and relaxation phenomena out of equilibrium. To access longer time scales and explore the emergence of Kondo-like physics, we employ the real-space NRG (eNRG) approach with a Wilson chain featuring uniform couplings over the first sites, followed by exponentially decaying couplings towards the end of the chain. The time evolution is performed using the Time-Evolving Block Decimation (TEBD) method. This strategy has previously shown excellent performance for non-interacting systems, and here we extend it to the interacting regime. We benchmark the resulting dynamics against those obtained using a uniform tight-binding chain and demonstrate that the Wilson chain accurately reproduces the dynamics while allowing access to significantly longer time scales. Finally, we analyze the real-time evolution of impurity-bath correlations, providing direct evidence for the emergence of Kondo-like physics in the interacting system.

11

• Queiroz Silveira, Lucas (Northeastern University, United States): Time and momentum resolved Floquet spectroscopy

Periodically driven quantum systems provide a powerful route to engineer novel states of matter by controlling their effective Hamiltonians through external fields. However, characterizing these transient regimes remains challenging, as conventional spectroscopic approaches often rely on equilibrium concepts that become inadequate. In this work, we introduce a time- and momentum-resolved tunneling spectroscopy protocol to probe the instantaneous energy structure of Floquet-driven systems beyond the high-frequency regime that does not depend on the prior knowledge of the entire spectrum.

12

• Rojo, Daniel Sikorski Cerqueira Cesar (UNESP – FEIS, Brazil): Exploring “Poor Man’s Majoranas” Stability with Spin-Exchange couplings

Our preliminary results (Sanches et al., 2026) reveal an environmental dissipative spectral stabilization effect: when the minimal Kitaev chain is coupled to multiple reservoirs and a single large spin S, the Poor Man’s Majorana (PMM) states exhibit enhanced stability against moderate fluctuations in the spin-exchange J. This finding suggests that engineered environmental coupling can provide partial localization of Majorana modes; As aftermath, we want to explore the response of QD dimers/trimers to electrostatic, spin-exchange and their correlations with possible previous signatures of non-trivial topological phases for long arrays of QDs, such as the “quadratic” and “cubic” power-law protections for QD dimers and trimers, respectively. In other words, our objective aims to investigate the “protection” of the PMM-based qubit in QD arrays that emulate short Kitaev chains. To address this issue quantitatively, we will employ the qubit dephasing timeT_{2}^{*} and its associated rate \frac{1}{T_{2}^{*}}\sim\frac{\delta\varepsilon}{\hbar}. This rate characterizes the loss of quantum coherence due to energy fluctuations \delta\varepsilon originating from environmental couplings. Specifically, for the Kitaev model with t=\Delta , the energy fluctuation stems from the splitting of the majorana bound sate (MBS) zero mode under a global shift of all on-site electrostatic potentials \ensuremath{\mu}. This leads to \delta\varepsilon=2\Delta\exp\left[-N\ln\left(\frac{2\Delta}{\mu}\right)\right]. This expression demonstrates that the splitting decreases exponentially with the number of sites N in the Kitaev wire, governed by the rate \ln\left(\frac{2\Delta}{\mu}\right). Consequently, \ensuremath{\frac{1}{T_{2}^{*}}} decreases with increasing N. Particularly, the specific case of the Kitaev dimer corresponds to the so-called “quadratic protection,” \delta\varepsilon=\frac{\mu^{2}}{2\Delta}, which evolves into the topological form for N\rightarrow\infty . In this project, we will reexamine this “quadratic protection” and the “cubic protection,” \delta\varepsilon=\frac{\mu^{3}}{4\Delta^{2}} for N=3, in the presence of asymmetric metallic leads and N on-site potentials induced by an overall shift of electrostatic and spin-exchange. A central question we will address is whether increasing the qubit dephasing time and improving quantum computing based on PMMs is feasible even with short Kitaev chains.

13

• Santos Dittberner, Luiz Felipe (Universidade de Brasília, Brazil): Finite-time quantum quenches in the XXZ spin chain: phase-transition fingerprints in dynamics and quantum thermodynamic indicators

This work investigates finite-time quantum quenches in the one-dimensional spin-1/2 XXZ chain, aiming to understand how different types of quantum phase transitions influence nonequilibrium state preparation. Starting from the ground state at Δ₀ = 0, the anisotropy parameter is linearly driven toward both the antiferromagnetic and ferromagnetic regimes, crossing either a Berezinskii–Kosterlitz–Thouless transition or a first-order transition. The dynamics is studied through exact diagonalization in finite chains, allowing the analysis of dynamical observables, entanglement properties, quantum work statistics, and spectral spreading. The results indicate that ramps crossing the BKT transition tend to approach the adiabatic regime as the ramp duration increases, with reduced excitation production and a work distribution more concentrated at low energies. In contrast, ramps across the first-order transition preserve strong non-adiabatic signatures even for longer driving times, showing broader work statistics and significant spectral mixing. Overall, the study highlights how equilibrium critical behavior directly affects finite-time quantum dynamics, with quantum thermodynamic indicators providing sensitive tools to characterize state preparation in strongly correlated many-body systems.

14

• Scalise, Levy (IPEN, Brazil): Electric Field Gradient as a Geometric Probe of Topological Quantum Matter

The electric field gradient (EFG), measured by techniques such as Time-Differential Perturbed Angular Correlation (TDPAC), Nuclear Quadrupole Resonance (NQR), and Mössbauer spectroscopy, is traditionally viewed as a set of local tensors at atomic sites. Here we propose a shift in perspective: treating the EFG as a continuous tensor field across the crystal, whose spatial organization can be analyzed using geometric concepts (principal-axis flows, tensor invariants, and singularities). We illustrate this approach with first-principles calculations on prototype Weyl semimetals. The resulting EFG fields display spatially structured patterns whose evolution can be compared with the topology of the electronic structure. This suggests that the geometric texture of the EFG may serve as a local, experimentally accessible witness of underlying electronic topology. Crucially, because the EFG reflects the anisotropy of the total charge distribution, its geometric organization is sensitive to symmetry breaking of any origin, including those emerging from correlations (e.g., nematicity, charge order, or interaction-driven topological phases). Our framework therefore opens a new observational window: hyperfine field geometry as a unifying language to probe both weakly and strongly correlated topological materials, with direct feedback to established nuclear spectroscopic methods. Rather than replacing established topological invariants, this framework seeks to complement them by introducing a real-space geometric description of hyperfine observables. By connecting local nuclear probes with global electronic organization, it opens new possibilities for interpreting spectroscopic measurements in topological and correlated quantum materials.

15

• Sokkalingam, Rajkumar (Ariel University, Israel): Pressure-Driven Evolution of Charge Density Wave and Antiferromagnetic Phases in RNiC₂ (R = Gd, Nd)

We present a comprehensive study of the pressure-induced evolution of charge density wave (CDW) and antiferromagnetic (AFM) phases in the rare-earth intermetallic compounds GdNiC₂ and NdNiC₂. High-pressure synchrotron powder X-ray diffraction experiments were carried out up to ~9 GPa, complemented by electrical transport measurements under pressure up to ~3 GPa. At ambient conditions, both compounds crystallize in the orthorhombic CeNiC₂-type structure (space group Amm2). With increasing pressure, the lattice parameters and unit-cell volume decrease monotonically without any structural phase transition, and the compression behavior is well described by a second-order Birch–Murnaghan equation of state. Transport measurements on GdNiC₂ at ambient pressure reveal three distinct anomalies associated with a CDW transition (~196.6 K), an incommensurate-to-commensurate CDW transition (~90.2 K), and an AFM transition (~22.6 K). Upon applying pressure, the CDW transition temperature is gradually suppressed from ~190.6 K at ambient pressure to ~184.5 K at 3.2 GPa. The AFM transition also shifts to lower temperatures and exhibits a change in the nature of the transition above ~2 GPa. Density-functional theory calculations for GdNiC₂ support the experimental findings and indicate significant modifications in the electronic structure between ~2.5 and 3.2 GPa. For NdNiC₂, ambient-pressure transport measurements show a CDW transition at ~106.5 K and an AFM transition at ~16.8 K. Both transitions are suppressed under pressure, with the CDW temperature decreasing to ~101.4 K at 3.0 GPa and the AFM transition to ~13.6 K. Our results highlight the strong coupling between lattice, electronic, and magnetic degrees of freedom in RNiC₂ compounds and demonstrate how external pressure effectively tunes competing ordered phases in correlated quantum materials.

16

• Telles De Miranda, Joaquim (Centro Brasileiro de Pesquisas Físicas, Brazil): Nonreciprocal fluctuations in noncentrosymmetrical superconductors

We present a theoretical framework for nonreciprocal nonlinear responses in superconducting systems with broken time‑reversal (T) and inversion (P) symmetries. In real materials inversion breaking can arise, e.g., from spin–orbit coupling or trigonal warping, while T is typically broken by an external magnetic field. In the superconducting phase these symmetry breakings give rise to diode effects, and in the normal state, just above Tc, superconducting fluctuations strongly enhance nonreciprocal responses. Using the time‑dependent Ginzburg–Landau (TDGL) formalism, we include symmetry‑allowed Lifshitz invariants in the GL free‑energy functional and compute the Aslamazov–Larkin and Maki–Thompson contributions to the nonlinear response. For Rashba‑type systems, a complementary Keldysh nonlinear sigma‑model analysis shows that nonreciprocal fluctuations modify the dissipative dynamics as well as thermodynamics. Our results give symmetry‑based predictions for enhanced nonlinear signals near Tc and identify observable signatures in nonlinear conductivity and diode efficiency.

17

• Vela Wac, Atilio (Instituto de física de líquidos y sistemas biológicos, Argentina): Competing quantum phases in a dipole-coupled model for one-dimensional polar metals

Polar metals have recently emerged as a fascinating class of quantum materials in which metallic conductivity coexists with broken inversion symmetry and polar distortions. Motivated by these systems, our research focuses on the numerical study of a one-dimensional strongly correlated model that combines electronic correlations, magnetism, and electric polarization. Using the Density Matrix Renormalization Group (DMRG), we investigate the ground-state properties of the system by analyzing magnetic, charge, and ferroelectric observables, with the aim of identifying the competing quantum phases and the mechanisms governing their stability. This work seeks to provide insight into the role of polar degrees of freedom in strongly correlated systems and to contribute to the understanding of emergent phenomena in low-dimensional polar metals

18

• Vicente, Filipe Manuel (UFABC, Brazil): Structural and optical characterization of single-crystal ZnP₂ and Pt/ZnP₂ junctions: charge transport and photoresponse.

In this work, ZnP2 single crystals were synthesized using the tin metal flux method. Structural, elemental, and optical characterizations were performed on ZnP2 single crystals, while charge transport and photoresponse were investigated in Pt/ZnP2 junctions. Powder X-ray Diffraction (PXRD) and Energy-Dispersive X-ray Spectroscopy (EDS) confirmed the monoclinic phase (P 21/c) and the stoichiometric elemental composition, respectively. By applying the Tauc formalism to diffuse reflectance measurements, an optical bandgap of 1.45 eV was determined. Although the I-V measurements, performed in the dark and under illumination (660, 605, and 470 nm), clearly exhibited rectifying behavior (RR ∼ 103), the thermionic emission, Schottky emission, and Poole–Frenkel conduction mechanisms failed to describe the charge injection process in the Pt/ZnP2 junction. Consequently, analysis of the log I versus log V plots in the voltage range from 1.1 to 5.0 V suggested that charge transport is dominated by the space-charge-limited current (SCLC) mechanism, with m > 5, indicating the presence of exponentially distributed trap states within the ZnP2 bandgap. The C-V analysis, performed at fixed AC frequencies, revealed capacitance peaks, suggesting contributions from interface charges and/or trap states. Furthermore, at each applied bias voltage, the capacitance decreased with increasing AC frequency. By applying the Mott–Schottky relationship to these measurements, the p-type nature of ZnP2 was confirmed, with a local acceptor concentration on the order of 1016–1017 cm−3. The photoresponse, investigated through transient photocurrent measurements, under negative bias voltages, was found to be governed by both band-to-band recombination and charge trapping processes. Regarding the device performance, the results indicate a responsivity on the order of 10−1 A/W, a specific detectivity on the order of 1011 Jones, and an external quantum efficiency ranging from approximately 4.4 to 24%. Overall, these results establish ZnP2 as a promising candidate for further optimization in photodetection applications. Keywords: ZnP2 Sn flux method, rectifying I-V curves, space-charge-limited current (SCLC), photoresponse.

19

• Silva Souza, Gabriel (Universidade Federal de Uberlândia, Brazil): Translation of skyrmions in spin-1/2 ferromagnetic lattices

In low-dimensional quantum magnets, the stabilization of topological excitations is driven by the interplay between lattice symmetry and competing energy scales. This work investigates a triangular spin-1/2 lattice where the competition between symmetric Heisenberg exchange ($J$) and antisymmetric Dzyaloshinskii-Moriya (DM) interactions ($D$) [1,2,3] gives rise to the emergence of skyrmion lattices, which are stabilized by external magnetic fields. These chiral spin textures are characterized by non-trivial topological charges and can be precisely manipulated via external magnetic fields. We propose a theoretical mechanism for skyrmion translation in ferromagnetic chains, using a quantum model that accounts for the discrete nature of spin-1/2 operators. We also analyze the diversity of spin textures and in the presence of second-neighbor interactions in the ferro- and antiferromagnetic models. Our results suggest a possible way of displacing quantum skyrmions in frustrated systems, offering a framework for future topological spintronic devices. References: [1] P. W. Anderson, Mater. Res. Bull. 8, 153 (1973). [2] B. Bernu et al., Phys. Rev. B 50, 10048 (1994). [3] T. Moriya, Phys. Rev. 120, 91 (1960).

20

• Farias Vasconcelos, Joao Lucas (Instituto de Física de São Carlos, Brazil): Intensifying superfluidity through atomic systems in mixed dimensions

This research aims to investigate the impact of long-range interactions on the quantum phase diagram of fermionic systems coupled to a three-dimensional bosonic bath. Building on a model designed to enhance p-wave superfluidity in two-dimensional fermionic layers, we analyze equilibrium states using advanced numerical techniques such as Quantum Monte Carlo simulations, which go beyond mean-field approximations. By exploring various confinement geometries—including infinite planes and bilayers—and considering dipole–dipole interactions mediated by phonon excitations from a Bose–Einstein condensate, we seek to identify exotic quantum phases and determine the critical conditions for superfluid transitions, paving the way for their future experimental observation.

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