Workshop on Frontiers in Quantum Materials

The search for novel emergent phases of matter has played a pivotal role in Condensed Matter Physics in the past few decades. In these phases, strong correlations, disorder and non-trivial topology of the electronic wave functions lead to quantum effects that leave fingerprints in a wide range of length and energy scales. Examples include high-Tc superconductors, topological insulators and semimetals that host robust surface states, and fractionalized excitations in quantum spin liquids. The capability of characterizing these exotic phases of matter at a fundamental level, predicting their occurrence in various materials, and taking advantage of on-demand manipulation of their properties for technological applications is attracting increasing interest in the broad and rich field of Quantum Materials. Among the open questions in the field, the correlation-driven topological states and the role of the quantum geometry of the wave functions beyond the Berry curvature in macroscopic properties of matter remain topics of intense debate. The ICTP-SAIFR Workshop on Frontiers in Quantum Materials brings together experts to discuss the most recent theoretical and experimental developments in the field of Quantum Materials. The exchange of ideas stimulated by the workshop will be a fertile ground for new collaborations between the participants.

• Eric Andrade (USP, Brazil)
• Rui Aquino (ICTP-SAIFR e IFT-UNESP, Brazil)
• Daniel Barci (UERJ, Brazil)
• Rafael Fernandes (University of Illinois Urbana-Champaign, USA)
• Eduardo Miranda (UNICAMP, Brazil)
• Thaís Victa Trevisan (IFSC-USP, Brazil)

Participants list here.

Announcement:

Click HERE for online registration

Registration deadline: July 8, 2025

Invited speakers

• Maria Carolina de Oliveira Aguiar (UFMG, Brazil)
• Flavia Alejandra Gómez Albarracín (IFLYSIB-CONICET, Argentina)
• Rodrigo Arouca (Uppsala University, Sweden)
• Turan Birol (University of Minnesota, USA)
• Eduardo Bittar (CBPF, Brazil)
• Marli dos Reis Cantarino (European Synchrotron Radiation Facility (ESRF), France)
• Vanuildo de Carvalho (Universidade Federal de Goiás, Brazil)
• Luis Gregório Dias (IF-USP, Brazil)
• Ian Fisher (Stanford, USA)
• Vivian França (UNESP, Brazil)
• Maria Gastiasoro (DIPC, Spain)
• Elena Gati (Max Planck Institute, Germany)
• Santiago Andrés Grigera (IFLYSIB-CONICET, Argentina)
• José Hoyos (IFSC-USP, Brazil)
• Na Hyun Jo (University of Michigan, USA)
• Mariana Malard (UNB, Brazil)
• Valentina Martelli (IF-USP, Brazil)
• Robert McQueeney (Iowa State University e Ames Lab, USA)
• Joe Meese (UIUC, USA)
• Paula Mellado (Adolfo Ibáñez University, Chile)
• Tobias Micklitz (CBPF, Brazil)
• Willian Natori (Unicamp, Brazil)
• Eduardo da Silva Neto (Yale, USA)
• Michal Papaj (University of Houston, USA)
• Gabriela Pasquini (UBA, Argentina)
• Rodrigo Pereira (UFRN, Brazil)
• Victor Quito (IFSC-USP, Brazil)
• Elya Esterlis (University of Wisconsin-Madison, USA)
• Dario Rosa (ICTP-SAIFR, Brazil)
• Carmen Rubio-Verdu (IFCO Barcelona, Spain)
• Jörg Schmalian (KIT, Alemanha)
• Inti Sodemann (University of Leipzig, Germany)
• Ricardo Urbano (Unicamp)
• Krissia Zawadzki (IFSC-USP, Brazil)

Announcement:

Click HERE for online registration

Registration deadline: July 8, 2025

Session duration:

-Plenary: 45+15

-Invited: 30+10

-Contributed: 20+10

Titles here

GROUP 1 (Monday and Thursday)

• Bellinati, Carlo (USP, Brazil): Towards more efficient matrix product state representations of fermionic Gaussian states

Both fermionic Gaussian states (FGS) and matrix product states (MPS) are classes of quantum states that proved to be very powerful for studying quantum many-body systems, particularly in the context of quantum spin liquid (QSL) phases. In recent years, several methods have been proposed to represent FGS as MPS, although existing approaches often face limitations that make their application numerically challenging. In this work, we propose a new method that integrates key ideas from previous algorithms to overcome these challenges. We benchmark our approach by testing Gutzwiller-projected variational wave-functions for the J_1-J_2 Heisenberg model on the triangular lattice, focusing on the QSL region of the phase diagram.

• Zorrer, Daniel (Instituto de Física de São Carlos / USP, Brazil): Revealing multipolar excitations and strong disorder signatures of spin chains using multidimensional spectroscopy

In order to characterize quantum many-body systems we introduce the technique of higher-order multidimensional coherent spectroscopy, in which a train of magnetic pulses interacts with the system and couples with its spins. We show that this technique unveils several hidden features in the linear response regime, highlighting multipolar and strong disorder features of spin systems. Besides that, the insertion of disorder in such systems changes their physics dramatically in comparison with the clean counterpart. In this context, we study a non-interacting disordered spin-1 ensemble and show how disorder broads the excitation peaks. Finally, we introduce the strong disorder renormalization group (SDRG) and show the first steps of how to analyze the multidimensional spectrum of disordered chains.

• Porlles López, David Fernando (Pontifícia Universidade Católica do Rio de Janeiro, Brazil): Quantum geometric origin of Meissner effect and superfluid weight marker

The momentum space of conventional superconductors is recently recognized to possess a quantum metric defined from the overlap of filled quasihole states at neighboring momenta. For multiband superconductors with arbitrary intraband and interband s-wave pairing, we elaborate that their superfluid weight in London equations is given by the momentum integration of the elements of quantum metric times the quasiparticle energy, indicating the quantum geometric origins of Meissner effect and vortex state. The momentum integration of the quantum metric further yields a spread of quasihole Wannier functions that characterizes the stability of the superconducting state. Our formalism allows the diamagnetic response of conventional superconductors to be mapped to individual lattice sites as a superfluid weight marker, which can incorporate the effect of disorder through self-consistently solving the Bogoliubov-de Gennes equations. Using single-band s-wave superconductors in 2D and 3D as examples, our marker reveals a diamagnetic current that circumvents nonmagnetic impurities, and the suppression of London penetration depth by disorder that is consistent with experiments.

• Dutra, Mateus Souza (Universidade Federal do ABC, Brazil): Spin Dynamics and Light-Induced Effects in the Narrow-Gap Semiconductor EuZn2P2

The 1-2-2 Zintl compound family containing the rare earth element Eu has attracted attention due to their promising properties as topological magnetic materials. However, the optoelectronic properties have not been studied: band gap modifications of Zintl phases makes them viable contender in the photovoltaic domain. Recent theoretical studies of promising Zintl materials have been reported, such as the case of SrCd2X2 (X = P, As) [1], BaCd2P2 [2], BaMg2X2 (X = P, As, Sb) [3], Ba2ZnP2 [4] and YbZn2X2 (X = P, As, Sb, Bi) [5], suggesting that Zintl compounds can improve the energy conversion efficiency and drastically reduce the production costs by taking advantage of the band structure engineering, since, the optical properties are related to their band structure. However, there are no experimental results for the Eu based family confirming these properties. We have decided to revisit the physical properties EuZn2P2 single crystals, by magnetization, specific heat, 151Eu Mössbauer spectroscopy, electron spin resonance, and electrical transport with light at room temperature. In the case of ESR, we can accurately obtain the response of Eu2+ neighbor as they interact with the Eu 4f electrons. Our analysis suggests that the emergence of internal fields interacting with the Eu2+ may give rise to magnetic polarons . For the electrical transport results with light, it was observed that the EuZn2P2 has a good photovoltaic response, transient and I vs V measurements. By these measurements, we want to show how good is EuZn2P2 as a platform to a wide range to explore a plethora of physical properties like: photonics, magnetism and electricity. [1] Manzoor, Mumtaz, et al. “Structural, electronic, optical, and thermoelectric studies on Zintl SrCd2Pn2 (Pn= P/As) compounds for solar cell applications: A First Principle Approach.” Journal of Solid State Chemistry 326 (2023): 124188. [2] Yuan, Zhenkun, et al. “Discovery of the Zintl-phosphide BaCd2P2 as a long carrier lifetime and stable solar absorber.” Joule 8.5 (2024): 1412-1429. [3] Souadi, G. “First principles investigations of optoelectronic and thermoelectric properties of novel BaMg2X2 (X= P, As, Sb) alloys for renewable energy applications.” Inorganic Chemistry Communications (2024): 112768. [4] Khireddine, A., et al. “Elastic, electronic, optical and thermoelectric properties of the novel Zintl-phase Ba2ZnP2.” Solid State Sciences 128 (2022): 106893. [5] Amin, Tahir, et al. “Structural, opto-electronic and transport properties of Zintl compound YbZn2Y2 (Y= P, As, Sb, Bi).” Engineered Science 31 (2024): 1258.

• Torrecilha, Elisa (Universidade de São Paulo, Brazil): Unusual ground states in frustrated magnets.

Frustrated magnetic systems exhibit numerous interesting and unexpected properties. A prime example is the antiferromagnetic Ising model on the triangular lattice. As one of the bonds in each triangle is always unsatisfied, the ground state is highly degenerate, which leads to extensive ground state degeneracy and algebraic spin-spin correlations at low temperatures. We can lift this degeneracy by applying an external magnetic field. For a small field, we quench the entropy, but the system still displays a critical phase and a Kosterlitz-Thouless transition. At higher fields, the system shows long-range order with the up-up-down arrangement of spins, i.e., in every triangle, the spin points against the field and two points along it. We have carefully studied all phases of the model, combining large-scale Monte Carlo simulations and analytical arguments.

• Picoli, Felipe Donizete (São Carlos Institute of Physics, University of São Paulo, Brazil): Tangent Krylov Solver : efficient matrix product state based computation of real-frequency spectral functions

We present a tangent Krylov method for the efficient computation of real-frequency spectra from ground-state matrix product states (MPS) obtained via the Density Matrix Renormalization Group (DMRG). The key idea is to project the resolvent operator onto the tangent space of the ground-state MPS, allowing for an accurate and compact Krylov-space representation. The novel approach enables the direct calculation of spectral weights along the real-frequency axis. We demonstrate the method’s robustness and versatility by applying it to a variety of systems, including the Haldane-Shastry model on a ring and interacting fermionic models, such as quantum impurity systems.

• Casellato, Fernando (Universidade Estadual Paulista (UNESP), Instituto de Química, Araraquara, Brazil): Circumventing convergence problems in the Kohn-Sham density functional theory approach

Density Functional Theory (DFT) has become the most widely used theoretical framework to describe electronic matter. In strongly correlated systems, such as the one-dimensional Hubbard model, a central challenge is to determine an accurate and appropriate exchange-correlation energy functional. Conventional DFT approaches often encounter convergence difficulties due to discontinuities in the exchange-correlation potential, particularly in magnetized and attractive regimes. In my Master’s research, I developed a fully functional numerical program that implements an alternative scheme based on the total energy LSDA (TLSDA) approach, inspired by the Bethe-Ansatz solution. This implementation successfully converges in scenarios where standard LDA methods fail, especially in attractive and polarized systems where magnetization induces intrinsic discontinuities. By employing TLSDA and carefully controlling the chemical potential, my code enables the exploration of exotic phases, such as possible FFLO-like states and topological insulating phases protected by magnetized superfluid edges. These results open new perspectives for investigating quantum phase transitions using entanglement entropy and density profiles as signatures, providing a powerful and computationally efficient tool for studying strongly correlated one-dimensional systems.

• Vicente, Filipe Manuel (UFABC, Brazil): Growth and structural characterization of RFe2Ga8 (R = Eu e Yb) single crystals by the flux method

The REFe2Ga8 family of materials have recently raised interest due to the observation of heavy-fermion-like properties and low-dimensional magnetic order in CeFe2Ga8 and SmFe2Ga8. However, there is a scarcity of other crystals with the same stoichiometric formula and different rare-earth elements. We report here the growth of single-crystals of EuFe2Ga8 and YbFe2Ga8, that are expected to crystallize in a orthorrombic structure with Pbam space group. These crystals have been grown by the self-flux method weighing stoichiometric amounts of Eu/Yb:Fe:Ga in the 1.5:2:20 ratio and placed into alumina crucibles sealed into quartz tubes under a low-pressure argon atmosphere. The materials and the quartz tubes were heated to 1150 °C kept for 2 h, slowly cooled to 750 °C over 100 h, and removed from the furnace, inverted and centrifuged to remove the excess flux. Needle-like crystals (Eu:Fe:Ga) and triangle-like crystals (Yb:Fe:Ga) were carefully separated from the growth. Structural analysis through X-ray diffraction experiments and Rietveld refinement, and Scanning electron microscopy (SEM) are being carried out at the moment and the results will be presented together with specific heat and magnetization measurements, that can give a hint about the possibility of having heavy-fermion behavior and magnetic order. The authors acknowledge CAPES and UFABC (CEM, LCCEM) for their support.

• Jofre Parra, Fabian (Pontifical Catholic University of Chile, Chile): Electron-phonon and Coulomb interactions in Weyl semimetals under strong magnetic fields and torsional strain

We study the presence of a strong magnetic field, in combination with torsional strain, over the electron-phonon and electron-electron interactions in a generic Weyl semimetal. This particular superposition of field and strain, modeled in the continuum approximation by an effective gauge field, leads to an asymmetric pseudo-magnetic field at each Weyl node with opposite chirality. Therefore, we also studied the role of nodal asymmetry on the properties of the system by means of the Wilson renormalization group and the corresponding Callan-Symanzik flow equations. By solving those, we discuss the evolution of the coupling parameters of the theory, and analyze possible fixed points leading to strongly correlated phases.

• De Figueiredo, Guilherme Fragoso (UNICAMP, Brazil): Topological signatures in a honeycomb antiferromagnetic Heisenberg model with symmetric and antisymmetric exchange interactions

In the present work, we calculate topological invariants (Chern numbers) and the thermal Hall conductivity for a columnar valence-bond solid (VBS) phase of a two-dimensional frustrated spin-1/2 antiferromagnet on honeycomb lattice. We consider an antiferromagnetic spin-1/2 J1-J2 Heisenberg model on a honeycomb lattice with an antisymmetric Dzyaloshinskii-Moriya (DM) exchange term between first and second neighbors and in the presence of an external magnetic field. Our focus is on the parameter region where the (quantum paramagnetic) columnar VBS phase is stable, as observed in previous numerical simulations for the model in the absence of the DM interaction. Using the bond-operator formalism, the original Hamiltonian is mapped onto an effective model that is expressed in terms of bosonic triplet operators. We study the effective boson model within a mean-field approximation, where triplet-triplet interactions are neglected. We apply numerical diagonalization techniques to diagonalize the effective quadratic (bosonic) Hamiltonian, then calculate the energy the elementary excitations (triplons) and determine the system’s phase diagram. Additionally, we compute the Berry curvature associated with the triplon bands, the corresponding Chern numbers, and, finally, the thermal Hall conductivity as a function of the temperature and the strength of DM interaction. While the presence of the Dzyaloshinskii-Moriya interaction yields a finite Berry curvature for the triplon bands, the associated Chern numbers vanish, indicating that the triplon excitations are topologically trivial. Interestingly, the observed thermal Hall conductivities are finite at low temperatures.

• Capelo, Gabriel (Universidade de São Paulo – Inistituto de Física, Brazil): Magnetization plateau in the kagome antiferromagnet

In the context of systems with localized magnetic moments, we call frustration the inability to satisfy all constraints imposed by the minimization of the local interaction energies. Frustration is intimately related to a macroscopic degeneracy in the ground state, which can be lifted by what is known as order-by-disorder mechanisms. One example of this is found in the magnetization process of a triangular lattice antiferromagnet, where quantum fluctuations select colinear phases, giving rise to an incompressible phase of a magnetization plateau in a finite range of magnetic field [1], with 1/3 of the magnetization of the fully polarized system. More recently, magnetization plateaus have been discussed in the Kagomé antiferromagnet, both with numerical methods[2] and in experiments[3]. As our Hamiltonian, we take the Heisenberg model in the kagome lattice with antiferromagnetic interaction between nearest neighbors and ferro/antiferromagnetic interactions between next-nearest neighbors coupled with an external magnetic field. We employ spin wave theory to show how this plateau phase can be described semiclassically, in close analogy with the same description in the triangular lattice. The method is a series expansion in powers of 1/S, where S is the size of the spin. Another way to explain the 1/3 plateau is in terms of a crystalization of localized magnons[4] based on the flat band in the magnon dispersion. We investigate this picture taking into account next nearest neighbours’ interactions J2, when the band acquires a small dispersion. We discuss the plateau width’s dependence on the spin size and the strength of J2.

• Vasques, Gustavo Gomes (Federal University of ABC, Brazil): Synthesis dependent charge density waves in PrPt2Si2

In this work, we present results from a comparative study of polycrystalline and single-crystalline PrPt₂Si₂ samples grown by both the flux and Czochralski methods. The samples were characterized using electron probe microanalysis, temperature-dependent single-crystal X-ray diffraction, magnetic susceptibility, specific heat, and electrical resistivity measurements. Unlike its neighboring compounds, LaPt₂Si₂ and NdPt₂Si₂, PrPt₂Si₂ exhibited a charge density wave (CDW) only in its polycrystalline form. This behavior may be similar to that of CePt₂Sn₂, in which the crystal structure slightly deviates from the P4/nmm space group at room temperature, allowing a structural distortion at the CDW transition temperature and/or the opening of a Fermi surface gap.

• Hembeck, Nicoly (IFGW/Unicamp, Brazil): Study of possible multipolar ordering in heavy fermion systems

We are studying realistic models with antiferromagnetic and multipolar (quadrupole and hexadecapole) orders for the compound CeRhIn5. This compound has an unexplained phase at high magnetic fields —evidenced by a strong and abrupt breaking of the tetragonal symmetry appears in the ab plane, detected through transport anisotropies and anomalies in the ultrasound propagation velocity. Our model aims to reproduce the experimental phase diagram and determine whether the observed symmetry breaking is indicative of multipolar ordering.

• Garcia, Fernando (Instituto de Física da Universidade de São Paulo, Brazil): Physical properties of RCo2Al8 single crystals (R= La, Ce, Pr, Nd and Sm): An emerging structure-type for anisotropic Kondo lattice studies

Systematic investigations of rare-earth ($R$) based intermetallic materials are a leading strategy to reveal the underlying mechanisms governing a range of physical phenomena, such as the formation of a Kondo lattice and competing electronic and magnetic anisotropies. In this work, the magnetic, thermal and transport properties of RCo2Al8 (R = La, Ce, Pr, Nd and Sm) single crystals are presented. LaCo2Al8 is characterized as a Pauli paramagnet and transport measurements, with the current along and perpendicular to the orthorhombic c-axis ($\rho_{c}$ and $\rho_{ab}$, respectively), reveal a clear electronic anisotropy, with $\rho_{ab }\approx(4-7)\rho_{c }$ at $300$ K. We show that CeCo$_{2}$Al$_{8}$ is a Kondo-lattice for which the Kondo coherence temperature $T_{\text{K}}^{*}$, deduced from broad maximums in $\rho_{c}$ and $\rho_{ab}$ at $\approx$ 68 and 46 K, respectively, is also anisotropic. This finding is related to a possible underlying anisotropy of the Kondo coupling in CeCo$_{2}$Al$_{8}$. The Pr and Nd-based materials present strong easy-axis anisotropy ($c$-axis) and antiferromagnetic (AFM) orders below $T=4.84$ K and $T=8.1$ K, respectively. Metamagnetic transitions from this AFM to a spin-polarized paramagnetic phase state are investigated by isothermal magnetization measurements. The Sm-based compound is also an easy-axis AFM with a transition at $T=21.6$ K.

• Mares, Jefter (IFSC/USP, Brazil): Entanglement signatures in the work statistics

Understanding entanglement structure in interacting many-body systems is fundamental for advancing efficient and scalable quantum technologies. This research quantifies the impact of quantum correlations on work extraction and injection within thermodynamic processes. This study employs paradigmatic models from condensed matter physics that describe various phases of matter, which are characterized not only by traditional order parameters but also by their entanglement properties.By establishing a relationship between the degree of entanglement and work extraction/injection, we aim to identify the energetic cost associated with accessing different quantum phases. This study provides crucial insights for developing protocols to manipulate quantum correlations and optimize the thermodynamic efficiency of processes in complex quantum systems.

• Galdino, João Armando Sandron (Universidade de São Paulo (USP), Brazil): Dynamical quantum phase transitions on disordered quantum Potts chains

We studied the time evolution of an extreme quantum quench for the quantum Q-state disordered Potts chain. For the extreme quench, it is possible to exactly map the Loschmidt echo onto a partition function in the complex plane by associating β=it. We showed using the transfer matrix technique that the order in which the bonds are distributed is irrelevant and that the dynamical phase transitions occur only for Q<4. For Q=2 (Ising model), we observed the existence of logarithmic divergences in certain situations. Additionally, we provide an interpretation of the transitions in terms of eingenvalue crossings. The novelty of this work was the ability to analytically derive expressions for the rate function (analogous to free energy) as a function of time and the extension for disordered systems of the interpretation of eigenvalue crossings for the dynamical phase transitions in 1D.

GROUP 2 (Tuesday and Friday)

• Leandro, Julia Perretto (IFGW-UNICAMP, Brazil): Classical Phase Diagram of a Frustrated Antiferromagnet

Magnetic frustration gives rise to exotic phases of matter, expanding the way that we can use and explore magnetism and quantum materials. In this study, our main goal is to build the classical phase diagram of the frustrated antiferromagnetic Heisenberg model on square and hexagonal lattices, incorporating J1-J2 interactions, along with an anisotropic Dzyaloshinskii-Moriya term. Using the Luttinger-Tisza method, we determine the ground-state spin configurations and analyze the emergence of ordered and disordered magnetic phases. Our investigation provides insights into the competition between exchange interactions and anisotropy, estabilising the first step to extend this model to its quantum counterpart.

• Braz, Lauro Barreto (Instituto de Física de São Paulo, Brazil): Interlayer interaction-driven s-to-dxy-wave superconductivity in La3Ni2O7 under pressure

Experimental and theoretical progress on the normal-state properties of the high-temperature superconductor La3Ni2O7 has provided evidence of strong interlayer interactions [1,2]. To better understand the effects of interlayer interactions in La3Ni2O7 under high pressure, we investigate a two-layer, two-orbital electron model that includes both intra- and interlayer Coulomb interaction terms within the framework of the matrix random-phase approximation. Our analysis reveals that interlayer interactions play a crucial role in determining the preferred superconducting pairing symmetry. Specifically, when interlayer interactions are included, a dxy-wave pairing symmetry is favored over the s-wave symmetry, which was previously found to dominate in their absence [3,4]. Furthermore, we find that interlayer interactions enhance interorbital pairing by incorporating contributions from all three electron pockets, which originate from both d3z²-r² and dx²-y² orbital characters. This results in the emergence of nodes in the superconducting gap function – features absent in the s-wave state – ultimately stabilizing the dxy-wave pairing symmetry. We acknowledge financial support of FAPESP, process 2023/14902-8. [1] T. Xie, M. Huo, X. Ni, F. Shen, X. Huang, H. Sun, H. C.Walker, D. Adroja, D. Yu, B. Shen, L. He, K. Cao, and M. Wang, Science Bulletin (2024). [2] X. Chen, J. Choi, Z. Jiang, J. Mei, K. Jiang, J. Li,S. Agrestini, M. Garcia-Fernandez, H. Sun, X. Huang, D. Shen, M. Wang, J. Hu, Y. Lu, K.-J. Zhou, and D. Feng, Nat. Comm. 15, 9597 (2024). [3] Y.-B. Liu, J.-W. Mei, F. Ye, W.-Q. Chen, and F. Yang, Phys. Rev. Lett. 131, 236002 (2023). [4] Y. Zhang, L.-F. Lin, A. Moreo, T. A. Maier, and E. Dagotto, Nat. Comm. 15, 2470 (2024).

• Nunes, Leandro Santos (UNESP – IGCE, Brazil): Some key aspects behind theories of Topological Insulators

In our work we treat some key aspects behind theories os Topological Insulators in a pedagogical way. So, first we deal with prototypes of Topological Insulators (TIs): the Hall Effects and some of his variations: –> Classical Hall Effect (HE); –> Integer Quantum Hall Effect (IQHE); –> Quantum Anomalous Hall Effect (QAHE); –> Quantum Spin Hall Effect (QSHE); After we make a comparison of conductivities and resistivities of HE, IQHE and Fractional Hall Effect (FQHE). So we adress the general theories of TIs: –> Topological Band Theory (TBT): non-interacting theory; –> Topological Field Theory (TFT): interacting theory; Finally we show the use of DFT of some candidate of TI material.

• De Souza Silva, Luan (Universidade de São Paulo, Brazil): Non-hermitian dissipative electronic systems with exact diagonalization

In this work, we solve numerically the 1D Hubbard model in the dissipative regime with a few sites using Exact Diagonalization (ED). To account for the dissipation, we use a (non-hermitian) Lindblad equation for the time evolution of the density matrix. As an initial density matrix, we use the density matrix given by the outer product of the ground state of the non-dissipative system. Further work will be done using the Density Matrix Renormalization Group (DMRG).

• Macêdo, Luís Eduardo Leite (UERJ, Brazil): Magnetic Excitations of a Nodally-Hybridized Heavy-Fermion Semi-metal: Application to CeNiSn

We examine the magnetic excitations of an Anderson Lattice Model with a V-shaped pseudogap resulting from nodal hybridization. The model pro duces a pseudogap in the electron density of states near the Fermi-Energy. This system is close to an antiferromagnetic quantum critical point and features low dimensional Fermi-Surfaces, aligning with experimental observations of CeNiSn. The Anderson Lattice Model with nodal hybridization exhibits degenerate pairs of one-dimensional Fermi-surfaces located at the center of the pseudogap. At energies slightly away from the Fermi-energy, the constant-energy cuts evolve into tori with small areas. We calculate both the static and dynamic magnetic susceptibilities, revealing distinct types of magnetic excitations. Analysis of the susceptibility suggests that the dynamic exponent at the quantum critical point is z = 1, differing from the usual dynamic exponent z = 2 found for metallic antiferromagnetic quantum critical points. Since the calculated magnetic spec tra compare favorably with inelastic neutron scattering data on CeNiSn (3), the model may help resolve the controversy surrounding interpretations of neutron scattering experiments

• Rabelo, Lucas Gabriel (Instituto de Física da Universidade de São Paulo, Brazil): Kondo screening and random singlet formation in highly disordered systems

In this work, we introduce the two-impurity Kondo problem as a minimal model to capture the anomalous low-temperature thermodynamics of doped semiconductors, such as Si:P, across the metal-insulator transition (MIT). In particular, we consider pairs of local magnetic moments coupled to a highly disordered, non-interacting electronic bath that undergoes a MIT as a function of doping. Using a large-N variational mean-field approach, we capture both the inhomogeneous local Fermi-liquid and the insulating random-singlet phase and find that the local moment susceptibility exhibits a robust power-law behavior, χ(T) ∝ T^(-α), with α evolving smoothly from 0.8 to 0.6 as doping increases before saturating in the metal. Our results highlight the competition between Kondo screening and random singlet formation as the key ingredients in constructing a complete theory for the low-temperature behavior of strongly disordered interacting systems.

• Oliveira, Lucas (PUC-Rio, Brazil): Robustness of topological order against disorder

A universal topological marker has been proposed recently to map the topological invariants of Dirac models in any dimension and symmetry class to lattice sites. Using this topological marker, we examine the conditions under which the global topological order, represented by the spatially averaged topological marker, remains unchanged in the presence of disorder for 1D and 2D systems.

• Inocêncio, Maria Vitória Tiago (UFMG – Universidade Federal de Minas Gerais, Brazil): Formation of Charge and Spin Ordering: Temporal Evolution After Quenches in One-Dimensional Interacting Systems

We investigate non-equilibrium phenomena in one-dimensional systems of strongly interacting electrons, focusing on the emergence of charge and spin order under quantum quenches. Starting from an initially disordered, non-interacting state, we simulate its time evolution within the half-filled extended Hubbard model with repulsive interactions, which hosts charge density wave (CDW) and spin density wave (SDW) phases. The interactions are gradually increased over a finite time interval until reaching these phases. The dynamics are analyzed using the time-dependent density matrix renormalization group (t-DMRG) method, implemented via the ITensor library, which enables efficient and accurate tensor network–based simulations. We identify three distinct temporal regimes during the quench — instantaneous, intermediate, and adiabatic — and examine the system’s behavior in the subsequent free evolution. The adiabatic regime leads to a stable post-quench state, while the instantaneous regime does not converge to the ground state and shows a significant increase in entropy. The intermediate regime exhibits oscillatory behavior in the order parameters, consistent across different system sizes.

• Neto, Marcello (Universidade Federal do Rio de Janeiro, Brazil): Quantum geometry and the electric magnetochiral anisotropy in noncentrosymmetric polar medi

The electric magnetochiral anisotropy is a nonreciprocal phenomenon accessible via second harmonic transport in noncentrosymmetric, time-reversal invariant materials, in which the rectification of current, I, can be controlled by an external magnetic field, B. Quantum geometry, which characterizes the topology of Bloch electrons in a Hilbert space, provides a powerful description of the nonlinear dynamics in topological materials. Here, we demonstrate that the electric magnetochiral anisotropy in noncentrosymmetric polar media owes its existence to the quantum metric, arising from the spin-orbit coupling, and to large Born effective charges. In this context, the reciprocal magnetoresistance is modified to include a linear contribution, where the chirality dependency is determined by the quantum metric dipole and the polarization. In 2D, we predict a universal scaling which we compared to available phase sensitive, second harmonic transport measurements on hydrothermally grown tellurium films under applied gate voltage. The control of rectification by varying I, P, B, and V, demonstrated in this work, opens up new avenues for the building of ultra-scaled CMOS circuits.

• Marinho, Marcus (USP, Brazil): Quantum Spin Liquids in Spin Ice Pyrochlores Stabilized by Disorder

Quantum spin liquids (QSLs) are exotic phases of matter characterized by long-range entanglement, emergent gauge structures and non-local excitations. Recent theoretical proposals suggest that in non-Kramers spin ice materials, the disorder can drive the formation of a Coulomb quantum spin liquid (CQSL). In particular, the presence of structural disorder in these systems can transform high-entropy classical spin ice into an entangled CQSL. We then have an unusual mechanism where defects stabilize a spin-liquid phase. Naturally, this scenario brings into question the stability of the CQSL with respect to the disorder itself. In particular, if the disorder is high enough, one can expect the CQSL to give room to a paramagnet. Interestingly, an intermediate Griffiths Coulomb quantum spin liquid (GCQSL) phase, akin to the well-known Mott glass phase, is expected to separate both. Mapping this problem to a random transverse field Ising model, we numerically investigate the effects of disorder on CQSL stability and identify regions in the parameter space where GCQSL emerges. Specifically, we explore the disorder-induced condensation of spinons, an exotic non-local excitation of the CQSL, to determine the complete phase diagram of the model. Our results provide quantitative insights into the conditions under which disorder supports or destabilizes the CQSL state, with direct implications for the candidate material Pr₂Zr₂O₇.

• Cavalante, Moallison Ferreira (UNICAMP, Brazil): Emergence of X states in a quantum impurity model

In the present work, we demonstrate the emergence of X states in the long-time response of a locally perturbed many-body quantum impurity model. The emergence of the double-qubit state is heralded by the lack of decay of the response function as well as the out-of-time order correlator, signifying the trapping of excitations and hence information in edge modes. Surprisingly, after carrying out a quantum information theory characterization, we show that such states exhibit genuine quantum correlations.

• Ikken, Nada (University Mohammed V in Rabat Morocco, Morocco): Modeling Bidirectional Quantum Teleportation over Structured Quantum Materials Using Quantum Walks

Quantum communication protocols rely heavily on entanglement distribution and coherence preservation across complex quantum networks. In this work, we explore a bidirectional quantum teleportation protocol based on quantum walks and evaluate its performance when implemented over structured quantum materials. By modeling coherent state transmission and entanglement transfer through a network of nodes governed by quantum walk dynamics, we investigate how the physical properties of the medium—such as lattice structure, decoherence rates, and material-induced noise—affect the fidelity and stability of quantum communication. Our approach combines theoretical modeling with simulation tools to study how quantum materials can enhance or limit teleportation across multi-hop paths. We focus on scenarios involving entangled states such as W-Bell and GHZ-Bell, and use fidelity and Bloch vector analysis to evaluate the quality of state recovery. This poster highlights the connection between quantum information theory and emerging material platforms, offering new insights into designing robust quantum communication systems supported by quantum materials.

• Villanueva Filho, Orion De Macedo Xavier (Institute of Physics of São Carlos at the University of São Paulo (IFSC/USP), Brazil): Approximations for the quantum work extracted from a correlated fermion system

The present project is inspired by the idea of approximating the work extracted in a quantum interacting system using Density Functional Theory (DFT). One of the key elements in DFT is the Kohn-Sham formulation, which converts the many-body problem in an effective non-interacting one by means of the so-called exchange-correlation functional. It has been shown that dealing with systems at finite temperature by means of DFT approximations built at previous works could produce accurate results up to a characteristic temperature. While in the previous studies for the quantum thermodynamics of the Hubbard model aforementioned the DFT approximations considered the exchange-correlation potential as that for the ground-state, an interesting route to improve their accuracy would be employing approximations constructed in the thermal DFT framework. In this project, we propose to study the extracted quantum work in the driven Hubbard model using density functional approximations. Our goal is to identify strategies for designing reliable approximations for quantities of interest of Quantum Thermodynamics in various correlation regimes and thermal ranges.

• De Assis Almeida, Patricia (Universidade Federal de Uberlândia, Brazil): The Kondo Effect in Mechanically Strained Kagome Lattices”

Kagome systems have received significant attention in recent years, primarily due to the discovery of several Kagome metals, such as AV3Sb5 [1]. These systems present rich physics that can be explored across different branches. Essentially, the Kagome lattice, in a tight binding description, is a 2D monolayer that features a unique band structure, combining dispersive bands-like graphene-with a completely flat band in its energy spectrum. This makes it an ideal system for analyzing both topology and correlation effects. Here, we focus on the latter by analyzing the Kondo effect in Kagome nanoribbons under the action of strain. To analyze the model itself, we use the Single Impurity Anderson Model (SIAM) and the numerical renormalization group (NRG). Our results indicate that by manipulating the strain, we can control the suppression or realization of the Kondo effect in our impurity-plus-ribbon system, as well as the size of the Kondo cloud.

• Farinas, Pedro Sanchez (IFSC, USP, Brazil): Effects of dissipation and disorder in systems with multiple order parameters and continuous symmetry

The effects of disorder in phase transitions are often studied in closed systems, where it leads to different and unexpected behavior of matter, such as Griffiths singularities, infinite-randomness criticality, and glassy behavior, to name a few. Because real materials are seldom closed systems, it is important to understand how the phase diagram of a system changes when coupled with other degrees of freedom. The combined effects of quenched disorder and Ohmic dissipation have been investigated for systems with continuous O(N) symmetry by Hoyos et al. (1,2). Their findings reveal that the phase transition is governed by an infinite-randomness fixed point, belonging to the same universality class as the random transverse-field Ising model. We aim to extend this framework to phase transitions involving multiple order-parameter fields, as the combined effects of dissipation and disorder remain largely unexplored in such cases. The study of systems with multiple order-parameter fields is particularly relevant in the context of iron-based superconductors, where phase transitions involve both s-wave and d-wave superconducting order parameters. Understanding how disorder and dissipation affect these transitions can provide valuable insights into the critical behavior of these materials, which remain an active area of research.

• Araujo, Ronaldo (Universidade Federal de lavras – UFLA, Brazil): Controlling Helical Edge State Leakage in Topological Insulator–Conventional Superconductor Interfaces

We investigate hybrid junctions composed of two-dimensional topological insulators (TIs) coupled to conventional superconductors (SCs), with the goal of analyzing the leakage of topologically protected helical edge states into the superconducting region. The system is modeled via a tight-binding Hamiltonian expressed in the Nambu spinor basis. We employ the Bernevig–Hughes–Zhang (BHZ) model to describe the TI and the Bogoliubov–de Gennes (BdG) formalism to simulate the superconducting region. Our results confirm that, as in other hybrid interfaces, edge states of the TI can penetrate into the SC region in TI–SC heterojunctions. We demonstrate that the extent of this leakage can be effectively tuned by introducing a chemical potential mismatch between the TI and SC regions. The deeper the TI band lies relative to that of the superconductor, the greater the spatial penetration of the edge state wavefunctions. We further examine the hybridization of edge states in TI–SC–TI junctions. We propose a transistor-like device whose logical operation is governed by the hybridization strength of edge states across the superconducting region, which can be modulated via an external gate. In the “on” state, the edge modes from both TI regions overlap within the SC region, forming a hybridized state that allows coherent current transport. In the “off” state, the lack of wavefunction overlap blocks current flow. This mechanism provides a viable route for topologically protected, gate-tunable quantum devices based on edge-state manipulation. [1] BERNEVIG, B. A.; HUGHES, T. L.; ZHANG, S.-C. Quantum spin hall effect and topological phase transition in hgte quantum wells. Science, v. 314, n. 5806, p. 1757–1761, 2006. [2] ZEGARRA, A.; EGUES, J. C.; CHEN, W. Persistent currents and spin torque caused by percolated quantum spin hall state. Phys. Rev. B, American Physical Society, v. 101, p. 224438, Jun 2020.

• Macêdo, Thales Freitas (Instituto de Física UFRJ, Brazil): Estimation of the electron-photon coupling in optical cavities

In this work, we address the inverse problem of estimating the electron–photon coupling strength from electronic transport measurements. Specifically, we propose a theoretical framework in which the cavity-modified conductance of a correlated electronic system is used as an indirect probe of the coupling intensity. Our approach provides a route to experimentally accessible estimates of light–matter coupling.

• Da Silva, Welberth (Instituto de Física – Universidade Federal do Rio de Janeiro, Brazil): Extended Hubbard model on the honeycomb lattice

The recent discovery of correlated insulating phases and superconductivity in magic-angle twisted bilayer graphene (TBG) has spawned renewed interest in the study of strongly correlated phenomena on a honeycomb lattice (HC). From a theoretical perspective, the Extended Hubbard Model (EHM) is one of the simplest models describing emergent magnetic, charge, and superconducting orders in electronic systems. Indeed, while a repulsive on-site interaction, $U > 0$, favors the formation of magnetic moments and their effective coupling, the presence of a repulsive nearest-neighbor interaction, $V > 0$, enhances charge correlations, thus favoring arrangements of doubly occupied sites. If one allows for attractive interactions in either the on-site or the nearest-neighbor channels, or both, one may wonder which pairing states may be stabilized in the ground state. With this in mind, here we use determinant quantum Monte Carlo simulations to probe the whole (i.e., the four possible combinations of $U$ and $V$ being positive or negative) phase diagram of the half-filled EHM on a HC lattice. The calculations have been carried out with complex Hubbard-Stratonovich (HS) auxiliary fields to yield sign-free simulations in the range $|V| \leq |U|/3$, in which case structure factors probing the ordered phases have been fed into correlation ratios; this allows for precise determination of critical boundaries through finitesize scaling analyses. Outside this region we use real HS fields and resort to additional local quantities, such as double occupancy and the average sign of the product of fermionic determinants, to determine the boundary of the CDW phase with a high degree of confidence. We have also established that only $s$-wave superconductivity is present, in marked contrast with the square lattice where $d$-wave pairs can be preferably stabilized. Further, as $|V|$ increases, the AFM phase demands larger values of U to stabilize. As expected, for sufficiently small $V < 0$, a phase separated region dominates the whole diagram for all $U$.

• Mariani Mattiello, Valéria (Universidade Estadual de Campinas, Brazil): Theory of a nematic phase of a heavy fermion compound: symmetry breaking in the hybridization channel

Electronic nematicity has been found in iron-based superconductors (see, e.g., [1]), where spin fluctuations drive a tetragonal to ortorhombic symmetry breaking. Recent STM/STS experiments have shown a similar C4-symmetry breaking in USbTe [2], a moderately heavy fermion compound. In this work, we show that a mechanism for the latter can be achieved by considering an infinite-U Anderson lattice with a tetragonal symmetry preserving hybridization term between localized fxyz and itinerant pz electrons. A Falikov-Kimball term, a Coulomb interaction term between f and p electrons (Uf p), then drives a nematic transition in the singlet f-p hybridization channel within the heavy Fermi liquid phase. A signature of this transition can be seen by computing the differential conductance probed in STM/STS measurements. Our work provides a novel mechanism for nematicity in the hybridization channel of heavy fermion compounds that emerges inside the heavy Fermi liquid phase.

• Tolentino Oliveira, Gabriel Aller (Instituto de Física “Gleb Wataghin”, Brazil): Magnetic Impurities in Topological Insulators: Application in EPR Results

Materials of the family of ternary semiconductors known as Half-Heuslers (HHs) have been shown to be candidates for topological insulators. Recent electron paramagnetic resonance (EPR) experiments [1, 2] in two HHs – YPtBi (topological) and YPdBi (trivial) – slightly doped with magnetic Nd3+ impurities have uncovered an intriguing behavior. In YPtBi, the experimental evidence suggests a regime with a strong phonon “bottleneck” effect such that bulk spins relax rather slowly to the lattice and the initial magnetization first diffuses slowly to the surface where coupling to gapless topologically protected surface states finally leads to a quick relaxation process. Based on this, we developed a description of the experimental results by considering the different responses of (a) bulk spins coupled to bulk bands and (b) spins in the surface region coupled to the gapless topological surface states. Using the the Dyson model [3], we adjusted the combined EPR responses of bulk and surface spins to the experimentally determined lines. We found that the larger the bottleneck effect, the stronger the effective contribution of surface spins, thus putting the previous interpretation of the experiments on a firmer theoretical basis.
We extend our analysis to the Gd-doped Kondo insulator SmB6, where recent experimental data [4] reveal an EPR response analogous to that observed in YPtBi. However, the strong temperature dependence of SmB6 resistivity obscures the diffusive component of the EPR signal, suggesting that a more refined model is required to fully explain the underlying phenomena.

Venue: The event will be held at the Principia Institute, located at Rua Pamplona, 145 – Domo – Bela Vista, São Paulo. It is located in the same block as the Hotel Intercity the Universe Paulista. See arrival instructions here.

Accommodation: Participants whose accommodation will be provided by the institute will stay at Hotel Intercity the Universe Paulista or Paulista Flat. Hotel recommendations are available here.

Attention! Some participants in ICTP-SAIFR activities have received email from fake travel agencies asking for credit card information. All communication with participants will be made by ICTP-SAIFR staff using an e-mail “@ictp-saifr.org”. We will not send any mailings about accommodation that require a credit card number or any sort of deposit. Also, if you are staying at Hotel Intercity the Universe Paulista, please confirm with the Uber/Taxi driver that the hotel is located at Rua Pamplona 83 in Bela Vista (and not in Jardim Etelvina).

BOARDING PASS: All participants, whose travel has been provided or will be reimbursed by ICTP-SAIFR, should bring the boarding pass  upon registration. The return boarding pass (PDF, if online check-in, scan or picture, if physical) should be sent to secretary@ictp-saifr.org by e-mail.

Visa information: Nationals from several countries in Latin America and Europe are exempt from tourist visa. Nationals from Australia, Canada and USA are required to have a tourist visa since April 10, 2025.

Poster presentation: Participants who are presenting a poster MUST BRING A PRINTED BANNER . The banner size should be at most 1 m (width) x 1,5 m (length). We do not accept A4 or A3 paper.

Power outlets: The standard power outlet in Brazil is type N (two round pins + grounding pin). Some European devices are compatible with the Brazilian power outlets. US devices will require an adapter.