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Physics Condensed Matter Strongly Correlated Electrons

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Monday 12 October

Strongly Correlated Electrons · Cross-listed from cond-mat.supr-con

Photon echo from Maki-Thompson interference in a fluctuating s-wave superconductor

Hui Zhou and Yuan Wan

We study theoretically the nonlinear optical response of a fluctuating s-wave superconductor driven by two successive terahertz pulses. We show that the response exhibits a photon echo signal that arises from the quantum interference between the time-reversed electron and hole trajectories in the Maki-Thompson process. By contrast, the transport of the fluctuating Cooper pairs responsible for the Aslamazov-Larkin conductivity does not generate an echo. The photon echo signal can be readily measured using terahertz two-dimensional coherent spectroscopy, highlighting its potential to distinguish different fluctuation conductivity mechanisms.
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Strongly Correlated Electrons

Thermally Enhanced Pseudo-Goldstone Spin Gap in the Isotropic Helimagnet ZnCr$_2$Se$_4$

N. D. Andriushin, A. Sanders, J. Reuther et al. (+8 more)

In magnetically ordered systems, the spin gap in the magnon spectrum is normally expected to decrease on warming and close at the transition out of the long-range order. The presence of a pseudo-Goldstone gap is commonly associated with nonlinear terms in spin-wave theory. However, its precise origin and detailed properties can vary and remain under debate. Here we show by means of inelastic neutron scattering that the pseudo-Goldstone gap in the Heisenberg helimagnet ZnCr$_2$Se$_4$ exhibits an atypical, nonmonotonic temperature dependence: the gap increases over much of the ordered phase before closing near $T_\mathrm{N}$. These results align with recent spin-dynamic simulations based on an effective quartic potential in an isotropic system~[Phys. Rev. B 113, L220411 (2026)]. As the pseudo-Goldstone spin gap in ZnCr$_2$Se$_4$ is dominated by quantum effects at subkelvin temperatures, its characteristic growth on warming is caused by thermal fluctuations.
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All authors N. D. Andriushin, A. Sanders, J. Reuther, D. C. Peets, P. Steffens, A. Hiess, J. Lass, L. Prodan, V. Tsurkan, V. Felea, D. S. Inosov

Strongly Correlated Electrons · Cross-listed from quant-ph

Finite-time quantum equilibration from local correlations

Piotr Ćwikliński

An isolated quantum system evolves reversibly, yet a small subsystem can lose nearly all information about its initial state. Conserved quantities may retain some of this information, depending on how strongly they overlap with local observables. Here we consider a subsystem in an arbitrary initial state coupled to a maximally mixed bath. We show that the worst-input mean-square equilibration error, maximised over window origins, is bounded from above and below by the mean square of a complete local autocorrelation, with the stationary part subtracted. A correlation record over a finite interval therefore controls the equilibration error in every interval of the same length. The result allows arbitrary degeneracies of energies and gaps. We apply it to two static Hamiltonian families. For fixed spin subsystems in the one-particle sector of a bounded-range periodic clock, fixed-accuracy thermalisation is guaranteed on windows that grow only slightly faster than linearly with system size, despite exponentially small positive energies. A random commuting model with logarithmic interaction range retains an extensive set of conserved observables. Its expected mean-square error is bounded by a finite-size term and an inverse-time term. The inverse-time dependence is unavoidable because of the initial transient. These examples show how local relaxation can coexist with exact conservation laws and a finely spaced spectrum.
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Strongly Correlated Electrons · Cross-listed from physics.ins-det

A Low-Temperature Tool for Acousto-electric Detection

Rohit Mandlik and Sunil Nair

We have developed an apparatus for the measurement of the acousto-electric effect (AEE) from room temperature to liquid nitrogen temperatures. The AEE is excited by bulk acoustic waves (BAWs) for which a lithium niobate piezoelectric actuator is employed. A very low background noise level is realized through careful electrical and mechanical design of the setup. The validity of the setup is tested by measuring the AEE in heavily doped P-type and N-type silicon. The opposite sign of the AEE signal was seen for both samples, showing dependence of the signal on the type of charge carrier being dragged by acoustic waves. The signal showed quadratic dependence on the driving voltage, which is consistent with the AEE literature. Further, a temperature dependence of the AEE signal was measured, which exhibits a monotonic increase with a rise in temperature. The ability to probe the AEE in bulk samples at low temperatures makes this setup a promising tool to investigate the AEE and related phenomena in different materials at cryogenic temperatures.
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Strongly Correlated Electrons

Field-driven phase transition crossover in kagome antiferromagnet Mn$_{3-x}$Co$_x$Sn

Shubhankar Paul and Chanchal Sow

Mn$_3$Sn exhibits a complex magnetic phase diagram with multiple symmetry-breaking phenomena. Minute electron doping at the Mn site breaks the kagome lattice symmetry in Mn$_3$Sn. In this work, we exploited this to tune the order of the magnetic phase transition using magnetocaloric effect in Mn$_{3-x}$Co$_x$Sn single crystals. Pristine Mn$_3$Sn shows metallic behaviour with a spin-reorientation transition at 278 K, which shifts to 175 K upon Co doping. Additionally, Co doping also induces a weak-ferromagnetic transition near $\approx 210$ K. The effect of Co doping results inverse to conventional magnetocaloric effect, with enhanced magnetic entropy change. Further, the scaled entropy change reveals a field-driven magnetic phase transition crossover from first order to second order in Mn$_{2.75}$Co$_{0.25}$Sn crystal. Based on experimental data, a new phase diagram is constructed, depicting the field evolution of various magnetic orders.
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Strongly Correlated Electrons

Electronic Structure of a Delafossite Oxide CuAlO$_2$ in Comparison with CuCrO$_2$

Kenta Takahashi, Ryo Kato, Mario Okawa et al. (+6 more)

We investigated the electronic structure of a delafossite oxide CuAlO$_2$ in comparison with CuCrO$_2$, using vacuum ultraviolet (VUV) and hard x-ray (HX) photoemission spectroscopy (PES) and band structure calculations within the local-density approximation +$U$ scheme. Cu 3$p\! -\! 3d$ resonant PES and Cu $2p$ core-level HX-PES give concrete evidence that the Cu valence in CuAlO$_2$ is monovalent, which makes a sharp contrast to CuCrO$_2$ that showed contradictory results depending upon probing methods [Yokobori et al., Phys. Rev. B 87, 195124 (2013)]. We further noticed weak but detectable satellite structures due to Cu$^{2+}$ state in the Cu $2p$ HX-PES spectrum of CuCrO$_2$, surprisingly, without an observable main peak due to the Cu$^{2+}$ state. Comparisons between the valence-band HX-PES spectra and the band structure calculations revealed a significant amount of the Cu $4s$ and Al $3s$/Cr $4s$ states in the valence band. The above results can reasonably be explained by the Cu $3d, 4s-$Cr $3d$ charge transfer model that we previously proposed in the above paper, thereby demonstrating the critical role of empty $3d$ orbitals in the electronic structure of the copper delafossite oxides.
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All authors Kenta Takahashi, Ryo Kato, Mario Okawa, Tetsuji Okuda, Akira Yasui, Eiji Ikenaga, Kanta Ono, Noriaki Hamada, Tomohiko Saitoh

Strongly Correlated Electrons · Cross-listed from quant-ph

Measuring higher-order bulk topology in a programmable quantum simulator

Pratik Sathe, Niclas Heinsdorf, Majid Kheirkhah et al. (+13 more)

Topological insulators lie outside the standard Landau paradigm: Instead of being characterized by local order parameters and spontaneous symmetry breaking, their defining properties are encoded in the global structure of their quantum states and manifested as robust boundary states. Crystalline higher-order topological insulators can extend this principle by hosting localized corner modes in two and higher dimensions. Although these boundary modes can be detected spectroscopically through the local density of states, determining the underlying bulk topology, for example through nested Wilson loops, remains an outstanding experimental challenge. Here we use up to 728 qubits in a superconducting analogue-digital quantum simulator to realize and probe a hierarchy of one-, two-, and three-dimensional topological insulators governed by effective tight-binding Hamiltonians. By reconstructing complex propagators from real-space measurements, we obtain complementary boundary and bulk characterizations: local densities of states reveal localized boundary modes, whereas experimentally reconstructed band projectors yield bulk topological invariants, culminating in a three-dimensional octupole moment extracted through third nested Wilson loops. These results establish a route to realizing, characterizing, and manipulating topologically protected states in programmable three-dimensional quantum matter.
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All authors Pratik Sathe, Niclas Heinsdorf, Majid Kheirkhah, Rahul Deshpande, Fabio Altomare, Andrew J. Berkley, Martin Dehn, Richard Harris, Emile Hoskinson, Stefan Paul, Gabriel Poulin-Lamarre, Jack Raymond, Chris Rich, Mohammad H. Amin, Marcel Franz, Andrew D. King

Sunday 11 October

Strongly Correlated Electrons

Magpie: A Graphical Magnon Software

Tobias Weber

Magpie is a fully graphical linear spin-wave software which has its main focus on 3-d visualisation of magnetic models and magnon dispersion relations. The software is distributed under an open-source license and is written in high-performance, portable C++. Its modular architecture allows for a rapid development of new calculation modules and permits the inclusion into external applications. Included code generators ensure seamless interoperability with other linear spin-wave libraries.
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Strongly Correlated Electrons

Variational Minimization of Almost Strong Zero Modes in Parafermionic Wires

Niklas Tausendpfund and Matteo Rizzi

Strongly interacting fermionic chains obeying a $Z_n$ symmetry can host topological phases with highly degenerate ground-state manifolds. The different ground states are connected by strongly bound fractionalized edge modes called parafermionic zero modes. While exactly preserved under time evolution at zero temperature, interactions lead to a destabilization of these modes at finite energy densities, and, given a generic Hamiltonian, obtaining the lifetime of these modes is often impossible as it requires knowledge of the full spectrum of the Hamiltonian or long time evolutions. Here, we propose a novel quantum-inspired algorithm that can be used to variationally search for these almost strong zero modes in generic parafermionic chain models. We demonstrate analytically and numerically that our ansatz faithfully reproduces the exact results and finds strongly bound parafermionic operators in the non-integrable Kitaev-Hubbard chain and chiral Potts model. Our results further allow us to verify the existence of a true strong zero mode in the symmetrical limit of the chiral Potts model for $Z_3$-parafermions.
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Strongly Correlated Electrons

Field Response of the Orbital Moment Probed by Integrated Magnetic Circular Dichroism

Qian-Sheng Shi, Ziqiang Wang, Jian Kang et al. (+1 more)

Magnetic circular dichroism (MCD) is an optical probe of orbital time reversal symmetry breaking. Although frequency integrated MCD is related to the self-rotation contribution to orbital magnetization at zero field, its magnetic response generally differs from the thermodynamic orbital susceptibility. Here, we define the MCD susceptibility and derive general expressions for multiband systems using an electromagnetic $U(1)$ gauge invariant approach. For insulators, the response contains contributions from the non-Abelian quantum metric, Berry curvature, and field induced interband mixing. For metals, a finite temperature Green function formulation separates the smooth response into Fermi sea and Fermi surface contributions. An independent Landau level calculation confirms the expressions for the zero-field MCD moment and its linear magnetic response. In a continuum model for twisted bilayer graphene, the MCD susceptibility vanishes within the charge neutrality gap, while the thermodynamic orbital susceptibility remains markedly diamagnetic. Near the gap edges, the orbital moment term dominates the response. Features near the van Hove energies are associated with density of states enhancement. These results clarify how the two susceptibilities reflect different orbital processes even for the same electronic structure and thus establish the MCD susceptibility as a distinct probe of orbital magnetic response.
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All authors Qian-Sheng Shi, Ziqiang Wang, Jian Kang, Yi Zhang

Strongly Correlated Electrons

Single-Particle Spectroscopy and Cross-Barrier Dynamics in Inhomogeneous Luttinger Liquids via Unified Field Bosonization Technique

Soundarya P, Venkata Suryanarayana M and Joy Prakash Das

The Unified Field Bosonization Technique (UFBT) is employed to investigate the single-particle properties of inhomogeneous Luttinger liquids containing localized clusters of impurities in the presence of forward-scattering interactions. Within this framework, fermionic two-point correlation functions are used to derive the leading-order singular contributions to the dynamical density of states (DDOS) and the cross-barrier tunneling conductance. The results reveal distinct power-law behaviours of the DDOS near the impurity cluster and in the far-field regime. The tunneling conductance exhibits a power-law temperature dependence, decreasing with decreasing temperature for repulsive interactions and increasing for attractive interactions, while remaining temperature-independent in the noninteracting limit. The impurity cluster modifies the amplitudes and spatial structure of these observables, whereas their characteristic power-law exponents are determined solely by the interaction parameters. The formulation accommodates arbitrary impurity strengths without requiring perturbative expansions in the impurity or interaction strengths. The characteristic scaling behaviour emerges directly from the fermionic correlation functions, without an explicit renormalization-group (RG) treatment of the impurity strength, while the weak-interaction limit recovers the leading perturbative correction to the tunneling response. These findings establish UFBT as a unified framework for describing local spectral properties and cross-barrier transport in inhomogeneous Luttinger liquids.
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Strongly Correlated Electrons

Realistic Simulation of Valence-band Photoemission Spectra by using First-principles Calculations on the Basis of FLAPW Method

Noriaki Hamada, Satoshi Nakamura, Kenta Takahashi et al. (+2 more)

In order to reproduce experimental photoemission spectroscopy (PES) data by using band structure calculations with linearized augmented-plane-wave method, we developed a new method to calculate the atomic-subshell photoelectron differential cross section (PE-DCS) of the valence band. PE-DCS was calculated to be the sum of the products of the partial density of states (PDOS) and the photoionization differential cross section (PI-DCS) of each atomic subshell. To construct an appropriate PDOS beyond the conventional muffin-tin sphere (MTS) PDOS, we proposed a “nearly-neutral atomic sphere", which can be defined as a natural extension of MTS. Although the calculational method for atomic-subshell PI-DCS was the standard Hartree-Fock-Slater method, we developed a new computer code in order to deal with the unoccupied electron shells in the ground state of isolated atoms up to $\sim$10 keV. Details of the PE-DCS calculations were examined by using two simple examples of Na metal and NaCl, and then, the method was applied to hard x-ray PES (HX-PES) data of CuAlO$_2$. The experimental spectra were satisfactorily reproduced, demonstrating the potential applications of our method to HX-PES spectra of many compounds.
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All authors Noriaki Hamada, Satoshi Nakamura, Kenta Takahashi, Mario Okawa, Tomohiko Saitoh

Strongly Correlated Electrons

Dynamical chiral symmetry breaking in rotating QED$_3$: critical flavor number and the occupation-reweighting channel

Wei Li

We study dynamical chiral symmetry breaking in $(2{+}1)$-dimensional QED on a rigidly rotating disc, $\Omega R<1$, within the rainbow Schwinger–Dyson framework. At zero temperature the rotation response of the condensate vanishes identically, so $N_c^{\rm SD}(\Omega,T{=}0)=N_c^{\rm SD}(0)=2.60\pm0.01$ (using three operational definitions). At finite temperature, rotation suppresses the condensate through a dominant occupation-reweighting channel, $\hat{\kappa}_{\rm occ}=-1.55$, accounting for $\ge 99.995\%$ of the linearized total response at the reference parameters, with self-consistent feedback amplifying it by $26.5$. The screening channel is reported at fixed regularization, $\hat{\kappa}_{\rm scr}(\varepsilon = 0.01)=-0.97$; its $\varepsilon \to 0$ behavior is logarithmically divergent. The crossover flavor $N^{*}(\Omega)$ falls monotonically at fixed temperature (a corollary). The critical flavor number is unchanged by rotation at $T=0$ (theorem). Together these results set the finite-temperature reference for the model.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

A Solvable Model in the Half-filled Landau Level

Anders Karlhede

A solvable microscopic model of interacting electrons in a half-filled Landau level is presented. The Hamiltonian is a well-defined limit of the electron-electron interaction. The low energy sector consists of a set of independent, spatially interlaced, one-dimensional systems of non-interacting fermionic dipoles, each system with a Fermi sea ground state. The total number of dipoles in the set of Fermi seas forming the two-dimensional ground state equals the number of electrons in the system and the density of states at the Fermi level is that of a two-dimensional Fermi gas. The model is obtained by generalizing, or rather adopting, the existing exact solution on a thin, but not too thin, torus to the two-dimensional bulk case.
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Strongly Correlated Electrons

Matrix-product-state GPLHR for non-Hermitian many-body eigenproblems

Xingyao Wu, Zhangyu Yang, Yanbin Chen et al. (+2 more)

Computing multiple eigenstates of non-Hermitian many-body operators plays an important role in investigating excitation spectra, spectral properties, and relaxation dynamics in interacting and open quantum systems. However, this task is challenging because the eigenvectors are generally nonorthogonal and the Hilbert space dimension grows exponentially with system size. Here, we formulate the generalized preconditioned locally harmonic residual (GPLHR) method in a matrix product state (MPS) framework to efficiently compute multiple targeted right eigenstates whose eigenvalues lie near a specified shift in the complex plane. Successive randomized compression (SRC) is employed to accelerate operator applications. We test the method on transcorrelated and complex Hubbard chains, an interacting non-Hermitian Su-Schrieffer-Heeger (SSH) chain, and a Liouvillian model. The results demonstrate that GPLHR combined with MPS provides an efficient and accurate approach for computing multiple eigenstates of non-Hermitian many-body operators.
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All authors Xingyao Wu, Zhangyu Yang, Yanbin Chen, Yu Wang, Feng Chen

Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

Microscopic foundation for orbitronics: orbital exchange interactions, orbital-dependent transport, and orbital switching

Hantao Zhang and Ran Cheng

Recent experiments highlighted the essential role of the orbital degrees of freedom underlying current-induced magnetic dynamics. However, a microscopic picture of how orbital angular momenta are transferred between itinerant and localized electrons, and the way it feeds back into transport, remains elusive. Here we develop a theoretical framework for the orbital exchange interactions by generalizing the Anderson-Kondo model to incorporate the orbitals of conduction bands. Illustrating with the $p$-orbitals, we determine the way electrons acquire orbital polarization and its influence on the transport properties, uncovering the orbital counterparts of phenomena analogous to spin filtering and tunnel magnetoresistance. Reciprocally, we demonstrate that orbital-polarized currents can exert torques on localized magnetic moments without having to convert into spin currents, which enables electrical switching of magnetization even when spin polarization becomes inactive. These striking discoveries lay a microscopic foundation for orbitronics and reveal critical mechanisms for orbital manipulations of magnetic order.
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Strongly Correlated Electrons · Cross-listed from hep-th

Holographic theory of non-invertible gravitational anomalies

Xiao-Gang Wen

We review a many-body formulation of gravitational anomalies as obstructions to realizing the complete low-energy data by a local bosonic lattice quantum system of the same dimension. In this formulation, an anomalous theory can be realized at the boundary of a gapped bosonic lattice bulk, whose topological order gives a one-to-one classification of the anomaly. An invertible bulk reproduces conventional anomaly inflow; a bulk with non-trivial topological excitations yields a non-invertible generalization. To describe the holographic theory of anomalies, we explain the distinction between uniquely defined topological order and many versions of topological quantum field theory and discuss the boundary-to-bulk map. As an application of the holographic theory of anomalies, we describe morphisms between local quantum theories (such as quantum field theories). These morphisms are built from a bulk domain wall and an invertible boundary junction, which give rise to a sandwich picture. Chiral boson/fermion theory, Laughlin edges, and boundaries of $\mathbb{Z}_2$ higher gauge theory with bosonic or fermionic point-like excitations illustrate the different kinds of information about non-invertible anomalies contained in transport coefficients, superselection sectors, and condensation data. In particular, a fermionic theory can be viewed as a theory with a particular non-invertible gravitational anomaly. Those examples also reveal that {\it symmetry $\sim$ gravitational anomaly $\sim$ topological order in one higher dimension}.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci

Framework for an AI-Ready ARPES Community Database

Zhi-Xun Shen, Jin Gene Wong, Karen Lei et al. (+41 more)

Condensed matter stands to gain profoundly from widespread adoption of artificial intelligence (AI). However, its current means of data organization impedes this endeavor. As a premier measure of electronic structure underlying material properties, Angle-Resolved Photoemission Spectroscopy (ARPES) has accumulated over four decades of spectra, yet the community's publication-centered workflow preserves only a highly selected fraction of its experimental record. A shared data ecosystem could transform these fragmented measurements and their contexts into a persistent, collective scientific memory, creating immediate value for reproducibility and reuse while laying the foundation for AI-enabled discovery. In this Perspective, we report outcomes of a recent community workshop and propose a practical path toward such an ecosystem. Its benefits unfold along three timescales. In the near term, standardized, searchable, and citable datasets strengthen analysis pipelines independently of AI. In the intermediate future, community-validated tools operating across laboratories could enable broader reuse and increasingly closed-loop automated experiments. In the long term, a diverse corpus of measured electronic spectra could support foundation models for quantum matter. Looking forward, a diverse corpus of measured electronic spectra could support foundation models for quantum matter and new discoveries. We discuss lessons from existing scientific databases, the current state of AI in ARPES, as well as areas of community convergence on data organization, access, credit, governance, and a staged pilot program.
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All authors Zhi-Xun Shen, Jin Gene Wong, Karen Lei, Leon Garcia, Felix Baumberger, Sergey Borisenko, Aaron Bostwick, Ting Cao, Tanny Chavez, Yulin Chen, Monika Choudhary, Andrea Damascelli, Dan Dessau, Thomas P. Devereaux, Sandy A. Ekahana, Alexei Fedorov, Atsushi Fujimori, Yucheng Guo, M. Zahid Hasan, Makoto Hashimoto, Yu He, Philip Hofmann, Zahid Hussain, Harold Y. Hwang, Zhurun Ji, Chunjing Jia, Timur K. Kim, Phil D. C. King, Takeshi Kondo, Alessandra Lanzara, Chun Lin, Donghui Lu, Matteo Michiardi, Sung-Kwan Mo, Brian Moritz, Laurenz Rettig, Eli Rotenberg, Takafumi Sato, Kyle M. Shen, Jonathan A. Sobota, Inna Vishik, Shuolong Yang, Ming Yi, Timothy Zaklama

Saturday 10 October

Strongly Correlated Electrons

Dispersion of low-energy optical excitations in NiPS$_3$ explained by singlet polaron theory

I. J. Hamad, C. S. Helman, A. E. Feiguin et al. (+2 more)

Optical and resonant inelastic X-ray scattering (RIXS) experiments in the van der Waals antiferromagnet NiPS$_3$ have revealed narrow excitonic resonances near 1.5 eV whose microscopic origin remains under debate. In this work we study the momentum dependence of these excitations using the singlet-polaron theory (SPT) previously developed for NiPS$_3$. Within its framework, we calculate the spectral function of the corresponding effective model and extract the dispersion of the resulting quasiparticles. The theory naturally predicts two singlet excitations whose dynamics arise from their propagation in the zig-zag antiferromagnetic background ($S=1$) coupled to two-magnon processes. We show that the dispersion of the lowest-energy quasiparticle agrees very well with the excitonic dispersion measured by RIXS, reproducing both its overall shape and bandwidth along high-symmetry directions of the Brillouin zone. Our results provide a consistent interpretation of the optical excitations in terms of dispersive singlet polarons, and suggest that similar mechanisms may govern excitonic dynamics in other layered van der Waals antiferromagnets.
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All authors I. J. Hamad, C. S. Helman, A. E. Feiguin, L. O. Manuel, A. A. Aligia

Strongly Correlated Electrons

Superlattice-Stabilized Fractional Chern Insulators in a "Berry Basin" Model

Yongxin Zeng and Andrew J. Millis

The discovery of integer and fractional Chern insulators in rhombohedral graphene, following their discovery in the isolated topological flat band in twisted MoTe$_2$, motivates a search for the conditions under which an electronic band can host a topological correlated state. In this Letter we introduce a “Berry basin" model which captures the essential features of rhombohedral graphene: a dispersive band with a flat bottom, momentum-space winding of a “layer" degree of freedom, and Coulomb interactions, while also including periodic potentials, enabling controlled studies of the interplay of quantum geometry, superlattice modulation, and electron-electron interactions in producing correlated topological states beyond the isolated topological band paradigm. While integer Chern insulators emerge at strong coupling without a superlattice potential, stabilizing the fractional state requires nonzero potential for all interaction strengths we access. We provide insight into the greater robustness of integer and fractional Chern insulators in rhombohedral graphene when electrons are polarized away from the moiré interface. Our results establish a new class of systems that host robust fractional Chern insulators and provide a controlled numerical platform to test competing theories of interacting topological phases.
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Strongly Correlated Electrons

Spectral Mapping Theorem between SU(N) and SU(Ns/N) Heisenberg Models and Exact Diagonalization of SU(4) and SU(7) Long-Range Ordered Phases on the Triangular Lattice

Samuel Gozel and Pierre Nataf

We first show that, for the SU(N) Heisenberg model with isotropic two-site interactions on an arbitrary lattice of Ns sites, the full spectrum in its singlet sector (when N divides Ns) is the negative of the full spectrum in its singlet sector of the SU(Ns/N) Heisenberg model defined on the same lattice. This theorem, valid for models with the fundamental irreducible representation (irrep) at each lattice site, follows naturally from a transposition operation in the basis of Standard Young Tableaux (SYTs). Second, this basis – previously recognized as particularly convenient for exact diagonalization (ED) of SU(N) Heisenberg models – admits an efficient, memory-saving implementation, thereby enabling large-scale diagonalizations for unprecedented system sizes Ns and numbers of colors N>3. We apply these ideas to an ED study of the SU(4) and SU(7) Heisenberg models on the triangular lattice (TL), extending the calculations up to Ns=28 sites. In particular, starting from the SU(4) case, whose nearest-neighbor ground state remains debated, we confirm that next-nearest-neighbor couplings stabilize four-sublattice long-range order. We further find that increasing the number of colors from N=4 to N=7 provides another route toward a Néel-like ground state, even without such additional couplings. N = 4 to N = 7 provides another route toward a Néel-like ground state, even without such additional couplings.
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Strongly Correlated Electrons

Emergent one-dimensional Bloch oscillations in coupled Ising layers

E. S. Ma and Z. Song

Bloch oscillations typically arise in periodic systems subjected to a constant force generated by a potential gradient. Here, we study domain-wall dynamics in coupled Ising layers under asymmetric longitudinal fields. The interlayer coupling is of Heisenberg type and acts as an effective transverse coupling in the emergent pseudospin representation. We show that the rung pseudospin structure gives rise to kinetic constraints, restricting the many-body dynamics to an emergent one-dimensional quasiparticle subspace within the original two-dimensional system. Furthermore, the imbalance between the longitudinal fields of the two layers induces an effective linear potential for the emergent domain-wall excitations, leading to their confinement between two oppositely polarized ferromagnetic domains. Remarkably, the resulting Wannier–Stark ladder of domain-wall excitations gives rise to Bloch oscillations in the absence of a conventional tilted potential, revealing a distinct mechanism for coherent quantum dynamics. Numerical simulations of time-dependent observables confirm the analytical predictions.
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Strongly Correlated Electrons · Cross-listed from math.QA

Lifts of symmetries to minimal nondegenerate extensions are unique up to fermion attachment

Ran Luo and Jiahua Tian

Gauging fermion parity in a $(2+1)$-dimensional fermionic topological order requires lifting its symmetries to the resulting bosonic theory. We give a direct tensor-categorical proof that, for a slightly degenerate braided fusion category $\mathcal{C}$ and a fixed minimal nondegenerate extension ${\cal E}$, the restriction homomorphism $r\colon\operatorname{Aut}_{\mathrm{LR}}(\mathcal{E})\to \operatorname{Aut}_{\mathrm{LR}}(\mathcal{C})$ on classes of complex-linear locality-respecting (LR) braided autoequivalences is surjective with central kernel $\mathbb{Z}/2$, generated by fermion attachment. Thus each symmetry class has exactly two LR lift classes, related by attaching the fermion to every vortex. We apply graded Morita theory to reduce the kernel to two module types on the vortex sector, corresponding to tensoring with the vacuum or the fermion. We then prove relative rigidity to show that each type determines a unique LR class, which are distinguished by fermionic self-braiding even when their actions on simple-object labels coincide. We prove surjectivity by extending graph algebras in $\mathcal{C}^{\mathrm{rev}}\boxtimes\mathcal{C}$ to Lagrangian algebras in $\mathcal{E}^{\mathrm{rev}}\boxtimes\mathcal{E}$. Our results require neither unitarity nor a ribbon structure. We illustrate the lifting ambiguity in the Laughlin state, the $SO(3)_3$ theory and the Ising topological order.
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Strongly Correlated Electrons

Exotic metallic phase in a heterotic Kondo lattice: violation of Luttinger's theorem and absence of Kondo gap

Hanting Zhong, Shuxiang Yang, Chao Cao et al. (+3 more)

Fermi surface transformation accompanied by quantum phase transition is widely observed in correlated electron systems including heavy fermion materials and van der Waals quantum heterostructures. The unified Anderson lattice description for this phenomenon suggests that their interacting ground states in the case of electron half filling always destabilize the metallic phase in the strong Kondo-coupling regime. We examine this issue within the paramagnetic phase of a Kondo lattice system with a heterotic layered structure. In the weak Kondo-coupling regime, the system exhibits a fractional Dirac liquid involving the massless or massive Dirac fermions and a charge neutral spinon Fermi surface. In the strong Kondo-coupling regime, the spinons hybridize with the Dirac fermions resulting in an intermediate nearly-flat hybridizing band together with the conduction and valence heavy fermion bands, yielding a large electric Fermi surface. Absence of the Kondo gap between these bands is observed depending on the stacking configurations of the layered structure. In particular, the system remains metallic even at the exact half filling in this regime and Luttinger's theorem is violated across the critical point. Implications of these results on the van der Waals quantum heterostructures are briefly discussed.
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All authors Hanting Zhong, Shuxiang Yang, Chao Cao, Xiao-Yong Feng, Jianhui Dai, Hai-Qing Lin

Strongly Correlated Electrons · Cross-listed from cond-mat.supr-con

Quantum Geometry and Pair Breaking in Intra- and Intervalley Superconductivity of Rhombohedral Graphene

Louis Primeau, Yang Zhang and Shi-Zeng Lin

The observation of superconductivity emerging from a spin- and valley-polarized normal state in rhombohedral graphene raises a basic puzzle: intravalley Cooper pairs involve states that are not generically degenerate because of trigonal warping, and therefore lack the particle–particle nesting underlying the conventional Cooper instability. While recent model studies suggest that nontrivial band geometry can strongly promote chiral pairing, how this geometric enhancement competes with realistic band-structure-induced pair breaking remains unclear. Here we study Kohn–Luttinger superconductivity in electron-doped rhombohedral tetralayer graphene using a DFT-fitted multiorbital tight-binding model, retaining the full Bloch-wave-function form factors in both RPA screening and the projected Cooper interaction. We separate the superconducting instability into three contributions: the symmetry-resolved form-factor-dressed interaction, the Cooper-pair phase space determined by the symmetrized pair dispersion, and the energy mismatch generated by trigonal warping. We find that the Bloch form factors strongly favor intravalley pairing, with a leading predominantly $p_x-ip_y$ instability and a substantially larger maximum $T_c$ than the intervalley reference state. At the same time, trigonal-warping-induced mismatch cuts off the Cooper logarithm and confines intravalley superconductivity to a much narrower region of the phase diagram. The dominant instability occurs near pair-Lifshitz transitions and primarily in reconstructed annular or three-lobed Fermi-surface regimes. Our results show that superconductivity in rhombohedral graphene is controlled by the combined effects of quantum-geometry-dressed interactions, pair fermiology, and trigonal-warping-induced pair breaking.
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Friday 9 October

Strongly Correlated Electrons · Cross-listed from hep-th

TheoPhysEval: Assessing AI agents at autonomous theoretical physics problem solving

A. Ramesh Chandra, Aaghaz Mahajan, Ainesh Sanyal et al. (+32 more)

We present a suite of 50 unpublished research-level theoretical physics problems with verifiable answers. Without AI assistance, a typical problem in our collection could be solved by a world expert in about a day or less but would take considerably longer for experts in adjacent specialties. We test the ability of off-the-shelf AI agents to tackle these problems autonomously, without human hints. When given access to tools available in a realistic setting, including the ability to search the literature and write scripts for numerical and symbolic work, the best-performing agent, GPT-6-Astra harnessed in Codex, obtains the final answers with a near-perfect accuracy of 98% at an average cost under USD 3 per problem. On average, agents show only small changes in accuracy when denied web search and access to background research papers, suggesting significant memorization of the literature. These results suggest that state-of-the-art agents can accurately perform concrete calculations required across theoretical physics research. We comment on the broader implications of these findings and discuss possible explanations for the current lack of agent-led breakthroughs in theoretical physics despite their outstanding problem-solving abilities.
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All authors A. Ramesh Chandra, Aaghaz Mahajan, Ainesh Sanyal, Mianqi Wang, Shubhadeep Chakraborty, Sudip Chakraborty, Shailesh Chandrasekharan, Rama Govindarajan, Akshit Goyal, Jonathan J. Heckman, Yasir Iqbal, Divya Jaganathan, Saumav Kapoor, Andreas Karch, Pushkar Khandare, Sandeep Krishna, Anupam Kundu, Alok Laddha, Tongyan Lin, Swarnendu Maity, Nilmani Mathur, Shani Nadir Meynet, Alessandro Mininno, Abhijeet Mishra, Vidur Niranjan, Abhishodh Prakash, Pratik Rath, Durbar Roy, Debargha Sarkar, Srikanth Sastry, Gary Shiu, Aninda Sinha, Thomas Van Riet, Praneeth Netrapalli, Suvrat Raju

Strongly Correlated Electrons

Exact SU($N$) symmetry resolution of bosonic Hubbard models: general boson-fermion mappings and flat-band singlet-cluster states

Loïc Herviou

We show how to perform exact diagonalization of SU($N$)-symmetric Bose-Hubbard models separately in each irreducible representation of SU($N$), by exploiting the Howe duality between U($L$) and U($N$). Three structural consequences follow for any lattice and any Hamiltonian built from the U($L$) generators: (i) the spectrum in a given orbital sector is independent of $N$ and of the particle statistics, (ii) the canonical partition functions for bosons and fermions obey the exact identity $Z_{\mathrm{b}}(-N)=(-1)^{N_\mathrm{b}}Z_{\mathrm{f}}(N)$, (iii) with unfrustrated hopping the groundstate is always a color ferromagnet, so that the color-resolved method we introduce is useful to study excited sectors, frustrated lattices and finite temperatures. As applications, we first derive the finite-temperature phase diagram of attractive SU($N$) bosons on few-site rings at large $N$ for arbitrary filling. We then show the emergence of singlet-cluster states from frustrated hopping, the counterpart of fermionic ferromagnetism, with the example of the sawtooth and kagome lattice.
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Strongly Correlated Electrons · Cross-listed from math-ph

Categorifying Quantum Spin Systems

Matthew Yu

We develop a homotopical framework for understanding the space of quantum spin systems based on topological $n$-nets, which assign associative unital algebras to local regions in an $n$-dimensional space in a manner that captures the locality structure of the underlying lattice theories. The net-theoretic perspective admits a natural categorification, in which the category of topological $n$-nets carries the structure of a higher Morita category. Moreover, the nets of greatest physical interest form a Karoubi-complete subcategory that shares many of the characteristic structural features of the category of finite TQFTs. Our main result identifies the group of locality-preserving symmetries of (3+1)-dimensional quantum spin systems (i.e. quantum cellular automata modulo stabilization, finite-depth quantum circuits, and translations) with the full Witt group of nondegenerate braided fusion categories, thereby answering a question posed by Haah.
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Strongly Correlated Electrons · Cross-listed from quant-ph

An entangling Hubbard quasiparticle collider on a digital quantum processor

Chan Bin Bark, Hanbyul Kim, Yoonil Koo et al. (+6 more)

Scattering of quasiparticles provides direct access to the interactions that govern strongly correlated systems. In this work, we realize the quasiparticle scattering experiment of the Fermi-Hubbard model on a digital quantum processor by colliding a doublon and a holon in the half-filled chain of 21 sites encoded on 42 qubits of the ibm_boston processor. For the first time, we measure the transmission probability of quasiparticles of the Hubbard model on quantum hardware, which agrees with the Bethe-ansatz scattering matrix without free parameters. Beyond the scattering probabilities, the collision generates entanglement by superposing the transmitted and reflected components, which we infer from the particle-number fluctuation. In sharp contrast, a control collision between two doublons shows neither the interaction dependence nor the number fluctuation, as expected for indistinguishable particles. Our work demonstrates that the ability to create quasiparticles of a chosen flavor on demand and program their motion and interactions makes a digital quantum processor a new experimental toolset for probing the entanglement structure generated by quasiparticle scattering.
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All authors Chan Bin Bark, Hanbyul Kim, Yoonil Koo, SeungBeom Hong, Seik Pak, Kwang Jun Ahn, Sangmo Cheon, Youngseok Kim, Moon Jip Park

Strongly Correlated Electrons · Cross-listed from hep-th

$q$-deformed Weil-Petersson Volumes from the Spectral Edge of DSSYK and Supersymmetric Extensions

Wasif Ahmed, Joydeep Naskar and Krishan Saraswat

The $q$-deformed Weil-Petersson volumes of Do and Norbury are the top-degree parts of Okuyama's discrete volumes, which are defined by topological recursion on the spectral curve of the double-scaled SYK (DSSYK) model. We show that the same q-deformed volumes can be obtained from a double-scaled matrix model whose disk density is found by zooming in on the soft edges of the DSSYK density. Applying the same procedure to the hard edge of $\mathcal{N}=1$ DSSYK, we obtain candidate $q$-deformed $\mathcal{N}=1$ super Weil-Petersson volumes. They are polynomials of fixed degree, and they reduce to the $\mathcal{N}=1$ super Weil-Petersson volumes in a scaled $q\to1$ limit. These candidate volumes differ from the $\mathcal{N}=1$ volumes of Do and Norbury in (arXiv:2510.12431) up to what we call "irrelevant" contributions which exactly vanish in the scaled $q\to 1$ limit. Together, these results demonstrate how q-deformed volumes can be naturally associated to the spectral edges of various DSSYK models and provides an intuitive way to construct them in supersymmetric contexts.
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