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Physics Condensed Matter Strongly Correlated Electrons

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Friday 7 August

Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci

Giant-exchange-driven Vectorial Control of a Minimal Topological Magnet in Eu3In2As4

Haonan Chen, Xunkai Duan, Guangyi Wang et al. (+13 more)

The interplay between magnetism and band topology provides a route to controlling quantum states of matter, yet its realization in materials is often constrained by weak exchange coupling and complex electronic structures. Here, a giant exchange coupling is identified in the newly predicted topological magnet Eu3In2As4, giving rise to magnetization-dependent band shifts of up to 300 meV. Together with its intrinsically soft magnetic response, this strong cou-pling enables systematic tuning of topological phases by both the magnitude and orientation of applied magnetic fields. The magneto-topological phase diagram is mapped out in which an antiferromagnetic topological insulator ground state evolves, under modest fields, into a pro-posed intermediate 2/3-ferrimagnetic phase, and further into fully polarized ferromagnetic states predicted to host either Weyl or nodal-ring semimetals. Notably, the Weyl phase corresponds to a minimal model hosting a single pair of Weyl nodes. Quantum oscillations, anomalous Hall transport and magneto-infrared spectroscopy consistently reveal exchange-driven band recon-struction across these transitions. Rotation of the magnetization theoretically provides an effi-cient means to tune the momentum-space positions and separations of the Weyl nodes. These results establish Eu3In2As4 as a model system for exploring how strong exchange coupling can be used to control topological band structures with minimal complexity.
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All authors Haonan Chen, Xunkai Duan, Guangyi Wang, Yuhan Du, Huayao Li, Jiayu Wang, Wenbin Wu, Zixuan Xu, Yingchao Xia, Jiaming Gu, Pengliang Leng, Lin Miao, Fengfeng Zhu, Xiang Yuan, Tong Zhou, Cheng Zhang

Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci

Universal Magnetoresistance Scaling in Layered Pd-based Multiband Metals Beyond Compensated Semimetal Regime

Kenjiro Okawa and Takao Sasagawa

We systematically investigated the magnetoresistance ratio (MR) of single-crystalline, nonmagnetic layered Pd-based metals, including centrosymmetric PdTe2, PdPb2, and beta-PdBi2 and noncentrosymmetric alpha-PdBi. Our study identifies a distinct class of large MR in multiband, high-carrier-density systems. Unlike well-studied extremely large MR materials, such as Dirac and Weyl semimetals described by simple compensated-carrier models, these compounds possess complex Fermi surfaces, as validated by our first-principles calculations. Nevertheless, they exhibit a remarkably simple MR scaling governed by carrier mobility, manifested in systematic dependencies on magnetic field, temperature, and the residual resistivity ratio (RRR). The validity of Kohler's rule in high-RRR crystals indicates that MR is governed by a single effective scattering time, even in these multiband systems. The field and RRR dependences of MR follow an intermediate power-law behavior between linear and quadratic, attributable to imperfect carrier compensation and a distribution of carrier mobilities. Among the studied compounds, alpha-PdBi exhibits the largest MR, reaching 1500% (2 K, 7 T), owing to its exceptionally high RRR (approximately 660). However, when compared on an equal-RRR basis, its MR is smaller than that of its centrosymmetric counterparts. This trend suggests that additional scattering channels arising from spin-orbit-induced band splitting in noncentrosymmetric systems reduce the effective carrier mobility. Our results establish a new class of large MR in clean multiband metals where complex electronic structures give rise to emergent single-parameter scaling, highlighting the interplay between disorder, mobility, and symmetry.
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Thursday 6 August

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

Observation of metastable chiral domain walls in a topological magnet

Richen Xiong, Chenxin Qin, Zhaoyu Han et al. (+17 more)

The interplay between topology and correlation can give rise to exotic collective excitations. The integer and fractional quantum anomalous Hall (QAH) magnets recently discovered in two-dimensional (2D) flatband systems are predicted to host spin excitations distinct from those in conventional magnets. Experimentally, nevertheless, these new excitations remain largely unexplored. Here we investigate spin-valley excitations in a twisted MoTe2 moiré superlattice using resonant ultrafast pump-probe spectroscopy. We observe a metastable spin-valley excitation in the QAH magnet below T ~ 3.7 K that survives reverse magnetic field several times larger than the saturation field. The behavior of this excitation is sharply distinct from ordinary domain walls and magnons, indicating a new type of spin-valley textures unique to topological magnets. We propose that these textures are chiral domain walls with an in-plane winding of the pseudospin order parameter along the domain wall. Their metastability arises from the interplay between the topological winding in real space and the quantum geometry of the parent bands in momentum space through a universal mechanism. These chiral domain walls govern the nonequilibrium dynamics of QAH magnets and may play a central role in their stability. Our study highlights intrinsic quantum geometry effects on spin excitations in topological magnets; and provides key insights into the fundamental mechanism limiting stability of topological protection.
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All authors Richen Xiong, Chenxin Qin, Zhaoyu Han, Nisarg Chadha, Qiang Gao, William Holtzmann, Weijie Li, Jiaqi Cai, Yi Guo, Weihanzhang Guo, Qi Chen, Samuel L. Brantly, Sam Bonkowsky, Chen Huang, Kenji Watanabe, Takashi Taniguchi, Andrea F. Young, Xiaodong Xu, Eslam Khalaf, Chenhao Jin

Strongly Correlated Electrons

Excitonic Magnetism in Ruthenium Pyrochlores

Swetlana Swarup, Yang Yang and Natalia B. Perkins

Strong spin-orbit coupling in $d^4$ systems is expected to stabilize a nonmagnetic $J=0$ singlet ground state, yet many ruthenium pyrochlores exhibit robust long-range magnetic order. Motivated by this apparent contradiction, we develop a microscopic theory of Van Vleck excitonic magnetism on the pyrochlore lattice. Starting from a multi-orbital Hubbard model with spin-orbit coupling, we derive the effective superexchange interactions within the low-energy singlet–triplet manifold of Ru$^{4+}$ ions. We analyze the resulting excitonic Hamiltonian using both the spectrum of triplon excitations and a variational treatment of the condensed phase. We identify the instability of the nonmagnetic singlet state toward triplon condensation and determine the resulting magnetic phase diagram as a function of the microscopic hopping parameters. The phase diagram reproduces the magnetic orders known from conventional pyrochlore models while also predicting an additional magnetic phase unique to the singlet–triplet description. Finally, we apply the theory to the pyrochlore ruthenates, with particular emphasis on Nd$_2$Ru$_2$O$_7$, and show that it lies in close proximity to the excitonic quantum critical point. Our results establish a microscopic framework for understanding excitonic magnetism in pyrochlore ruthenates and their magnetic excitation spectrum, providing direct connections to spectroscopic probes, including Raman scattering.
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Strongly Correlated Electrons · Cross-listed from quant-ph

KPZ Superdiffusion of Local Correlators in Diffusive Random Quantum Circuits

Ewan McCulloch

We study the single-particle Green's function $G(x,t)=\langle \sigma^-_x(0)\sigma^+_0(t)\rangle$ in one-dimensional particle-number-conserving random unitary circuits coupled to an external bath. For fixed spacetime disorder, we argue that $G(x,t)$ is governed, in both the strong- and weak-noise limits, by directed waves in a random medium. We find Kardar-Parisi-Zhang (KPZ) scaling in the wandering statistics of the normalized spatial distribution $p(x,t)\propto |G(x,t)|^2$ and in the associated free energy. In particular, its center $\langle x(t)\rangle\equiv\sum_x x\, p(x,t)$ wanders on a length-scale $\mathcal{O}(t^{2/3})$, while sample-to-sample fluctuations of $-\log\sum_x |G(x,t)|^2$ scale as $t^{1/3}$. At weak noise $\gamma \ll 1$, the crossover to the strong-disorder fixed point occurs at a parametrically long time $\mathcal{O}(\gamma^{-3/2})$. These predictions are confirmed numerically using tensor-network simulations of the noisy operator dynamics in individual circuits at moderate noise, and of a phase-annealed proxy retaining hopping disorder at weak noise.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci

Sublattice-resolved coherent phonon dynamics in charge density waves

Kyoung Hun Oh, Honglie Ning, Zongqi Shen et al. (+15 more)

Phonons govern fundamental material properties and play a central role in various electronic phase transitions. Coherent driving of specific phonon modes enables on-demand phase control, motivating sublattice-resolved identification of real-space phonon motions. Yet experimentally resolving these motions remains challenging, limiting precise phonon-based control. Here, we introduce a dynamical protocol to track element-resolved phonon dynamics in the charge density wave material EuTe4, in which the dominant Te-sublattice charge order is accompanied by a previously unreported Eu-sublattice component. We leverage the elemental selectivity of time-resolved resonant X-ray scattering to reveal three coherent phonon modes with distinct sublattice character, thereby disentangling Eu- and Te-dominated lattice dynamics, in good agreement with theoretical calculations of the phonon eigenvectors. This time-domain approach, which surpasses the energy-resolution limits of conventional frequency-domain inelastic scattering, provides a broadly applicable framework for decomposing coherent phonons in multi-element materials, which is crucial for the targeted control of phases of matter.
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All authors Kyoung Hun Oh, Honglie Ning, Zongqi Shen, Yifan Su, Jack Maier, Gyeongbo Kang, Hyeongi Choi, Dong Wu, Qiaomei Liu, Hyun-Woo J. Kim, Seunghyeok Ha, Jaehwon Kim, Byungjune Lee, B. J. Kim, N. L. Wang, Yao Wang, Hoyoung Jang, Nuh Gedik

Strongly Correlated Electrons

Composite Fields and Tree Expansions: A Unified Framework for Renormalized Vertex Decompositions

Oleksandr Sulyma and Benedikt Schneider

One-particle irreducible vertices encode renormalized interactions in quantum field theories, but their practical treatment remains challenging due to their high dimensionality and nontrivial dependence on external variables such as momenta or frequencies. We develop a functional framework that algebraically reorganizes the diagrammatic content of the vertex functions into more efficient building blocks and reveals several established vertex decompositions, such as parquet, single-boson exchange, asymptotic classes and symmetric estimators, as different realizations of a common functional structure. Based on Legendre transforms of the effective action of composite fields, the formalism shows that different vertex representations arise from different choices of composite degrees of freedom. We demonstrate that in our framework higher-order vertices can be systematically obtained via tree expansions, thereby extending the aforementioned decompositions beyond the four-point level. Because our findings are independent of any specific physical setting, the framework applies broadly to quantum field theories in condensed matter physics, particle physics, and beyond.
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Strongly Correlated Electrons

Phonon spectral functions of low-density polaron metals

Luis Walther, Alberto Nocera and Mona Berciu

We use the density matrix renormalization group (DMRG) to compute the phonon spectral function of a one-dimensional spinless Holstein model doped with a low but finite carrier concentration, $x \leq 0.15$, as a function of the electron-phonon coupling $\lambda$. To the best of our knowledge, these are the first such results in this regime, complementing extensive prior work at the single-polaron level ($x\to 0$). We find that significant phonon spectral weight is transferred both below, all the way down to $\omega=0$, and above the bare phonon energy $\Omega$, in stark contrast with the Kohn-anomaly phenomenology expected in the Migdal limit, where weight remains centered near $\Omega$ with a kink at $q=2k_F$. No signature of this $2k_F$ kink appears in our results. This behavior is captured qualitatively by the Random Phase Approximation (RPA), and semi-quantitatively, at negligible extra computational cost, by a “dressed RPA” scheme in which the electron addition propagator is renormalized using the Momentum Average (MA) approximation for the low-density electron-polaron. By contrast, adding the lowest-order vertex correction to this dressed scheme produces unphysical negative spectral weight, signaling that vertex and propagator dressings must be treated consistently once the propagators are dressed nonperturbatively. Our results provide an efficient approximation for the phonon spectral functions of low-density polaron metals, a regime relevant to weakly doped insulators.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

Multi-State Geometry of Density Matrices and Rectification Sum Rules

Barry Bradlyn

The geometry of quantum states has emerged as a key ingredient in understanding the linear and nonlinear responses of quantum materials. To date, however, the connection between geometry and nonlinear response is best understood for clean, noninteracting systems at zero temperature. In this work, we develop a theory of multi-state geometry for density matrices and use it to derive sum rules for second-order rectification, making no assumptions about the strength of disorder or interactions. We first show that perturbation theory for thermal density matrices gives rise to two dual information-theoretic connections and an almost complex structure. We introduce a complex, quantum generalization of the Amari-Chentsov tensor of classical information theory, the cQAC tensor, which captures the multi-state geometry of the perturbed density matrix. We derive a zero-temperature sum rule for the frequency-integrated DC rectification response of an insulator as a difference between a ground state third cumulant and the complex distortion tensor, a multi-state geometric quantity built from the cQAC tensor. This generalizes known single-particle sum rules for the shift and nonlinear Hall currents to many-body systems and general perturbations. Specializing to the shift current, we resolve the geometric contribution for multiband insulators into particle-like and hole-like terms. We verify the sum rule numerically in a generalized Kane-Mele model, finding that the geometric contribution can dominate the integrated response. Finally, we show that although the splitting of the sum rule into cumulant and geometric contributions does not survive at nonzero temperature, the measured sum rule for insulators differs from its zero-temperature form by corrections exponentially small in the gap, allowing low-temperature rectification measurements to probe the multi-state geometry of insulators.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Approximate Quantum Error Correction at Chiral Topological Edges

Yuntai Song, Zejun Liu, Zhencheng Wang et al. (+2 more)

Topologically ordered phases naturally realize quantum error correction through nonlocal encoding of quantum information. More recently, conformal field theories have been shown to realize approximate quantum error-correcting codes, but such constructions generally require fine tuning to criticality. Here we introduce a family of approximate quantum error-correcting codes realized by the chiral edges of two-dimensional topologically ordered phases. The proposed encoding combines the robustness of a gapped topological bulk with the flexibility of gapless edge conformal field theories. To characterize its robustness, we study coherent-information loss under local erasure. We derive an exact expression relating coherent-information loss to relative entropy, reducing the recoverability problem to universal properties of the edge theory. This leads to power-law scaling of coherent-information loss with the size of the erased region. We further show that, for geometrically local erasures near one edge, the two-dimensional chiral edge code is at least as robust as the dimensionally reduced CFT code, and is strictly more robust in several representative examples. For Abelian code subspaces, we further construct a power-law-range recovery map supported on the erased region together with a power-law-range buffer; this recovery map depends only on the code subspace, not on the unknown encoded state. We provide numerical calculations for lattice realizations of compact free boson and Ising CFT examples that support the theoretical predictions of the power-law exponents.
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All authors Yuntai Song, Zejun Liu, Zhencheng Wang, Jong Yeon Lee, Bowen Shi

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

Anyon-Impurity Bound States in Quantum-Engineered Fractional Chern Insulators

Botao Wang, Amit Vashisht, Felix A. Palm et al. (+3 more)

Mobile impurities provide a powerful means of probing correlated and topological quantum matter, through their dressing by the surrounding medium and the practical probes granting access to the resulting composite object. Motivated by the recent observation of anyon-impurity composites in the solid state, as well as recent realizations of Laughlin-type states in engineered lattice systems, we investigate the formation of a bound state between a mobile impurity and a single pinned quasihole in the interacting Harper-Hofstadter model deep in the fractional Chern insulator regime. Combining analytical arguments with large-scale numerical simulations, we characterize the structure, energetics, and stability of hybrid anyon-impurity bound states, and show that their binding energy provides direct access to the fractional charge of the quasihole under conditions that we identify. We further demonstrate that the composite object can be coherently transported by externally steering the quasihole pinning potential. Our results establish a realistic pathway for controlled anyon-impurity manipulation in quantum-engineered platforms, enabling experimentally feasible protocols for braiding.
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All authors Botao Wang, Amit Vashisht, Felix A. Palm, Fabian Grusdt, Laurens Vanderstraeten, Nathan Goldman

Strongly Correlated Electrons

Neural Flux Attachment: From Bose Condensates to Chiral Topological Matter

Rudik Badalyan, Khachatur G. Nazaryan and Tigran A. Sedrakyan

Can one neural wave function describe both a Bose condensate and a chiral topological liquid? We introduce ChernFormer, which combines a fermionic transformer with a fixed Chern-Simons phase that attaches one statistical vortex to every particle pair. Each factor changes sign under exchange, so their product is exactly bosonic. The fixed phase changes statistics but not probability, making every bosonic learning problem equivalent to a fermionic one with the same approximation error and overlap. With enough capacity, ChernFormer can approximate any normalizable bosonic wave function on the plane at fixed particle number. A finite, smooth network still vanishes when particles meet, yet this contact hole can shrink while the wave function and condensate fraction approach those of a nodeless condensate. Following the needle-in-a-haystack target-reconstruction benchmark introduced in \cite{NazaryanGaggioliTengFu2025}, we test ChernFormer on the Kalmeyer–Laughlin ground state and its first two chiral edge states. The overlap curves stay close to unity through their largest sampled sizes, while independent amplitude and phase maps at $N=20$ for all three states recover both local Laughlin vortices and the collective edge vortex. By contrast, a continuous, nonzero product of identical particle-wise factors misses these elementary edge sectors. ChernFormer therefore provides one variational language for conventional bosonic order and chiral topological matter.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

An Effective String Theory Toolbox for Quantum Hall Interfaces III: Open Worldsheets, Endpoint Conditions, and Branes

Ken K. W. Ma

A freely moving quantum Hall (QH) interface may end on a physical edge or topological boundary, but fixed-edge theory cannot determine what endpoint data make such a termination consistent. Here we formulate an open-worldsheet junction framework in which the embedding, material charge, anomaly flow, and topological boundary condition are organized together. The endpoint is specified by a geometric support and variational boundary data, together with condensable topological sectors and any outgoing channels required to absorb or continue the worldsheet flux. This construction extends the charge–shape relation to an interval and shows why a lone chiral Majorana cannot terminate on a finite-dimensional endpoint degree of freedom. It gives an operational definition of a QH brane and a systematic basis for endpoint and network theories of dynamical QH interfaces.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

An Effective String Theory Toolbox for Quantum Hall Interfaces II: Majorana Fermions on Fluctuating Moore-Read Worldsheets

Ken K. W. Ma

A Moore–Read interface carries a chiral Majorana mode on a boundary whose geometry may itself fluctuate. Fixed-edge theory does not determine how this neutral mode should be transported when the interface bends and moves, or how its dynamics couples to the fluctuating shape. Here we construct a spatially reparametrization-invariant Majorana theory on the nonrelativistic worldsheet of a freely moving interface. The changing line element fixes a universal half-density transport law, while additional curvature- and velocity-dependent couplings remain controlled by microscopic interface physics. The resulting framework identifies the Majorana stress tensor as the mediator between neutral and geometric dynamics and provides the neutral sector needed for effective theories of dynamical non-Abelian quantum Hall interfaces.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

An Effective String Theory Toolbox for Quantum Hall Interfaces I: Worldsheet Kinematics and Constraint Structure

Ken K. W. Ma

A freely moving quantum Hall interface is fundamentally different from an ordinary edge fixed by an external confining potential. Since a normal displacement changes the areas occupied by the adjacent incompressible phases, the interface geometry and charge dynamics cannot be treated as independent degrees of freedom. We formulate this problem for interfaces between Abelian quantum Hall phases using a spatially reparametrization-invariant worldsheet description, in which tangential motion is a relabeling of the interface while normal motion is physical. Starting from the two-sided Chern–Simons response, we derive the relation between normal charge transport and interface motion. We then introduce a relative-area construction, defined with respect to a material reference curve, that converts this velocity relation into an equal-time constraint linking the charged boundary sector to the interface shape. Combined with the folded $K$-matrix current algebra, this identifies the universal Hall kinematics of the moving interface while leaving its geometric energy and neutral dynamics dependent on microscopic interface physics. The resulting framework provides a systematic basis for effective theories of dynamical quantum Hall interfaces.
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Strongly Correlated Electrons

Resilient strange metal at an unconventional quantum critical point in $d=2$

Jérôme Leblanc and A.-M. S. Tremblay

Properties of the two-dimensional Hubbard model with nearest-neighbor hopping are under scrutiny in cold-atom experiments and diagrammatic quantum Monte Carlo. Given the controlled nature of these approaches, it is timely to make predictions about strange-metal behavior and its relation to quantum-critical properties. Even for interaction strengths below the Mott transition, several peculiarities occur at the quantum critical point separating Fermi liquid and incommensurate spin-density wave order. Here, we predict, using the non-perturbative improved two-particle self-consistent approach, that for correlation lengths ranging from about one to one hundred lattice spacings, Kohn anomalies on the underlying Fermi surface lead to unconventional critical exponents. The temperature dependence of the single-particle self-energy acquires strong momentum dependence along the Fermi surface with no clear evidence of Landau quasiparticles. Nevertheless, we observe strange-metal behavior, namely, resistivity that scales linearly with temperature as $T\rightarrow{0}$. Our work shows that a linear temperature dependence of resistivity arises without a linear-in-temperature self-energy along the Fermi surface, as is often assumed.
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Strongly Correlated Electrons

Dissipation-induced bulk and boundary criticality in the Haldane chain

Zhenjiu Wang and Manuel Weber

We study the Haldane chain coupled to a dissipative ohmic bath. Using large-scale quantum Monte Carlo simulations, we identify a second-order quantum phase transition into an antiferromagnetic state with spontaneously broken SO(3) symmetry that is governed by an interacting fixed point with dynamical exponent $z\approx 2$. We derive a generalized string order parameter which indicates that the symmetry-protected topological ground state of the Haldane chain is stable for weak dissipation and develops a nontrivial scaling dimension at criticality. In particular, its topological edge modes display nontrivial boundary criticality that is distinct from an equivalent transition out of a trivial state; for the latter, we perform an accurate $\epsilon$ expansion of a dissipative $\phi^4$ theory with ordinary boundary conditions. Our setup realizes a spin impurity in a critical yet nonconformal antiferromagnet and paves the way for continuously tunable boundary criticality controlled by dissipation.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Field-Space Entanglement Dynamics Between Tunnel-Coupled Luttinger Liquids

Léonce Dupays, Taufiq Murtadho, Bi Hong Tiang et al. (+2 more)

Entanglement dynamics depend not only on how a quantum system is partitioned, but critically on how interactions across that partition are structured. For a spatial bipartition of a locally interacting system, entanglement is generated near the boundary and then propagates into the bulk. By contrast, when two extended quantum fields are coupled locally along their entire length, the interaction crosses the field-space partition everywhere, and this generates correlations throughout the system. Here, we study the entanglement dynamics between two gapless one-dimensional quantum many-body systems described by Luttinger liquid theory. The systems are initially decoupled and prepared at zero or finite temperature, after which a time-dependent tunneling interaction is activated uniformly along their length. Within a Gaussian approximation, we derive general analytical expressions for the logarithmic negativity, mutual information, and Rényi entropies under arbitrary coupling protocols. At zero temperature, entanglement displays an early-time power-law growth whose exponent is fixed solely by the first non-null derivative of the tunneling protocol. Once the coupling saturates, we obtain exact long-time averages of the information-theoretic quantities and characterise how the correlations scale with temperature and the final coupling strength. We also analyse how mutual information and logarithmic negativity approach the adiabatic limit for a very slow protocol with respect to intrinsic system timescale. This work extends the study of entanglement dynamics in nonequilibrium field theory to field-space partitions and mixed initial states.
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All authors Léonce Dupays, Taufiq Murtadho, Bi Hong Tiang, Nelly H.Y. Ng, Paola Ruggiero

Strongly Correlated Electrons

Landscape of incompressible crystals of hard-core bosons on the square-kagome lattice

Pratyay Ghosh

We investigate a hard-core boson model on the square-kagome lattice using hierarchical mean-field theory beyond the conventional unit-cell description. We show that the conventional description of the square-kagome lattice based on its smallest unit cell does not fully capture the hierarchy of incompressible states supported by the lattice, but only captures the two compact-localized-state-based phases at densities $5/6$ and $2/3$. Within our approach, we reproduce these previously established phases and uncover additional incompressible states enabled by enlarging the variational cluster. Among these, the $\rho=3/4$ phase is found to be particularly robust, which, through the Matsubara-Matsuda mapping, corresponds to a half-magnetization plateau in the spin-$1/2$ XXZ model. We further apply our approach to two experimentally relevant square-kagome compounds using exchange parameters obtained from first-principles calculations. The calculated magnetization processes are in good agreement with available experimental results and predict additional plateau structures in these materials.
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Strongly Correlated Electrons

Correlated topological-polarization surface states in the narrow-gap insulator FeSb2

Takahiro Iwagaki, Hideki Matsuoka, Ginta Hoshino et al. (+7 more)

Strong electron correlations and band topology each generate rich quantum phases, but conflicting elemental requirements have largely kept them apart. Topological polarization offers a route to unite them, producing polar surface states from bonding charge without spin-orbit coupling and thereby extending band topology to correlated 3d transition-metal compounds. Here we demonstrate that epitaxial thin films of the narrow-gap insulator FeSb2 host metallic polar surface states of topological-polarization origin, governed by the strong correlations of the bulk. Nonreciprocal surface transport emerges only below the onset temperature of a correlation-driven reconstruction of the bulk Fe 3d orbital occupation, providing direct evidence of bulk-edge correspondence in a correlated topological system. Moreover, electrostatic gating drives this correlated surface across a quantum phase transition into a ferromagnetic or possibly altermagnetic state. Our results establish topological polarization as a design principle for correlated topological phases in a broad range of materials.
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All authors Takahiro Iwagaki, Hideki Matsuoka, Ginta Hoshino, Kanata Watanabe, Shungo Aoyagi, Shunsuke Kitou, Yuiga Nakamura, Motoaki Hirayama, Takashi Koretsune, Naoya Kanazawa

Strongly Correlated Electrons

Helical-to-Fan Transitions under Magnetic Fields in the Noncentrosymmetric Tetragonal Magnet EuRhGe$_3$

Takeshi Matsumura, Hiroto Nitta, Hironori Nakao et al. (+4 more)

The magnetic structure of EuRhGe$_3$, a noncentrosymmetric body-centered tetragonal magnet with the space group $I4mm$, has been investigated by resonant X-ray diffraction. Below $T_{\text{N}}=12$ K, EuRhGe$_3$ undergoes a helical magnetic ordering with an incommensurate propagation vector $q=(0, 0, 0.809)$, in which the magnetic moments lie in the $ab$ plane and rotate by a constant turn angle of $145.8^{\circ}$ between adjacent layers. When a magnetic field is applied along the $a$ axis at 2 K, a second-harmonic $2q$ peak develops, indicating that the circular helix is gradually distorted into a helimagnetic soliton-lattice state, which eventually undergoes a lock-in transition to the commensurate structure with $q=0.8$ at 3.8 T. Above the subsequent phase boundary at 5 T, the helicity is lost, and a spin-flop $xyz$-fan (elliptic conical) state is realized, in which the moments oscillate predominantly along the $b$ axis but are accompanied by a small $c$-axis component. At higher fields, the system enters a conventional planar $xy$-fan phase without a $c$-axis component. EuRhGe$_3$ provides a prototypical example of a helimagnet that exhibits a full sequence of field-induced structures, evolving from a circular helix to a spin-flop $xyz$-fan (elliptic conical), and finally to a planar $xy$-fan structure, which has been theoretically predicted.
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All authors Takeshi Matsumura, Hiroto Nitta, Hironori Nakao, Masashi Kakihana, Masato Hedo, Takao Nakama, Yoshichika Ōnuki

Strongly Correlated Electrons

Local Spin Excitations Mediate Quasiparticle Breakdown in the Orbital-Selective Mott Phase

Yuekun Niu, Yu Ni, Jia-Ming Wang et al. (+3 more)

The orbital-selective Mott phase (OSMP) is commonly described as a coexistence of localized and itinerant electrons within effectively decoupled orbitals, but emerging evidence for quasiparticle breakdown points to physics beyond this picture, whose microscopic origin remains unknown. Using dynamical mean-field theory for the two-band Hubbard model, we show that the spin-flip and Ising-type components of Hund's coupling generate local spin excitations (LSEs). These LSEs couple electrons between different orbitals, renormalize quasiparticle lifetimes and binding energies, and thereby destroy well-defined quasiparticles in the OSMP. Removing these two components of Hund's coupling restores coherent quasiparticle behavior and fully decouples the charge dynamics of the two bands. Our results therefore identify electronic coupling to LSEs as the fundamental mechanism driving quasiparticle breakdown within the OSMP.
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All authors Yuekun Niu, Yu Ni, Jia-Ming Wang, Zhong-Yi Lu, Yun Song, Shiping Feng

Strongly Correlated Electrons

Strongly Enhanced Charge-Density Waves and Correlated Insulating State in Atomically Thin 1$T$-TaS$_2$

Gan Liu, Yulu Liu, Qiling Luo et al. (+7 more)

We investigate thickness-dependent charge-density-wave (CDW) transitions in 1$T$-TaS$_2$ using temperature-dependent Raman spectroscopy and electrical transport. Raman measurements show that the incommensurate, nearly commensurate, and commensurate CDW phases persist down to the monolayer limit. As the thickness is reduced, the transition temperatures increase, accompanied by an orders-of-magnitude rise in sheet resistance and a sharp reduction in the carrier localization length. The first-order hysteretic CCDW-NCCDW transition is uniquely absent in the monolayer. Calculations suggest that the enhanced CDW in thin layers originates from strengthened Coulomb interactions due to reduced out-of-plane screening, particularly in the nonlocal component. These findings highlight the cooperative roles of electron correlation, electron-phonon interaction, and interlayer coupling in shaping the ground state and transition dynamics of atomically thin 1$T$-TaS$_2$, opening pathways for engineering correlated phases in two-dimensional CDW systems.
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All authors Gan Liu, Yulu Liu, Qiling Luo, Zhentao Huang, Kenji Watanabe, Takashi Taniguchi, Meiyu Wang, Jinsheng Wen, Yi Lu, Xiaoxiang Xi

Wednesday 5 August

Strongly Correlated Electrons

Self-dual $S_3$ gauge theory in 2+1d: lattice model and topological phase transitions

Da-Chuan Lu, Chong Wang and Ashvin Vishwanath

Electric-magnetic self-duality of the $\mathbb{Z}_2$ gauge theory, realized microscopically as a half-lattice-translation exchanging electric charge and magnetic flux, has been an influential example of a duality symmetry with an exact lattice realization. We construct the first non-Abelian generalization of this construction: a lattice model of the $S_3$ quantum double $\mathcal{D}(S_3)$ on a tensor product Hilbert space in which the $\mathbb{Z}^{\mathrm{em}}_2$ anyon-permutation symmetry, exchanging the non-Abelian chargeon $C$ and fluxon $F$, is realized via lattice translation. Consequently we find that the zigzag boundary termination of the model realizes, without fine-tuning, a gapless critical edge state described by the tetracritical Ising CFT. The bulk admits three independent $\mathbb{Z}_2^{\mathrm{em}}$-preserving bosonic perturbations, driving $\mathcal{D}(S_3)$ into distinct gapped phases. We analyze these transitions by three independent methods: category-theoretic anyon condensation, microscopic lattice Hamiltonians, and Chern-Simons-Higgs theory, which all agree, yielding a unified picture. These examples motivate a minimal-condensation principle: proliferating a bosonic anyon generically drives condensation of a minimal condensable algebra containing it, with symmetry-related condensates appearing as degenerate vacua that spontaneously break the anyon-permutation symmetry. Our model construction extends to an infinite family of self-dual dihedral quantum doubles $\mathcal{D}(D_{2n})$. Notably, each model is sign-problem-free, opening the door to large-scale numerical exploration of the phases of non-Abelian Chern-Simons-Higgs theories.
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Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Theory of Measurement-Altered Criticality

Kabir Khanna, Sara Murciano and Romain Vasseur

Local measurements can alter long-range correlations in gapless quantum matter. We propose a theory of weakly-monitored Tomonaga-Luttinger liquids, a broad class of quantum critical states in one dimension. In order to address the intrinsic randomness of the measurement record, we develop a replica instanton calculation to study Born-averaged observables. We find that when measurements are relevant, average correlators of density and phase fluctuations decay at long distances as universal power laws with logarithmic corrections, a feature we argue is peculiar to measurement-induced randomness. We characterize the full multifractal spectrum of moments of correlations functions, revealing broad, strongly non-gaussian fluctuations across the ensemble of post-measurement states. We support these analytic results with matrix-product-state calculations, and provide a general picture of measurement-altered criticality for ground states described by 1+1d conformal field theories. Our results establish that physical measurements alter critical quantum states in a manner that lies beyond both forced measurements and conventional critical scaling.
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Strongly Correlated Electrons

Superconducting and charge-ordered phases from Dirac quantum spin liquids on the triangular lattice

Andreas Feuerpfeil, Ronny Thomale, Subir Sachdev et al. (+1 more)

Triangular-lattice quantum spin-liquid insulators are observed to undergo transitions to superconductivity under pressure or doping, and exhibit enhanced terahertz conductivity when driven by mid-infrared light. We present a general theoretical framework for the emergence of superconducting and charge-ordered phases from a U(1) Dirac spin liquid with fermionic spinons, as well as from its gapped $\mathbb{Z}_2$ and chiral descendants. Numerical studies have provided substantial evidence for these spin-liquid states. The spin-liquid phase hosts fractionalized Dirac spinons coupled to an emergent gauge field, whereas the superconducting and charge-ordered phases are conventional, with neither fractionalized excitations nor emergent gauge dynamics. The transition between these phases is driven by the Higgs condensation of spinless charge-$e$ bosonic chargons (“doublons” and “holons”). We show that the projective symmetry group of the Dirac spinons uniquely determines the symmetry and dispersion of the chargons, allowing us to construct an effective low-energy theory near the chargon band minima. Gauge-invariant composites of the chargon Higgs fields provide the order parameters characterizing the phases. The resulting phase diagram contains a rich variety of ordered states, including $d+id$ superconductivity, charge-density waves, bond-density waves, and pair-density waves.
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All authors Andreas Feuerpfeil, Ronny Thomale, Subir Sachdev, Pietro M. Bonetti

Strongly Correlated Electrons

A fractional quantum Hall factory on quantum processors: constant-depth preparation of clustered non-Abelian states

Cheng Xu, Ching Hua Lee, Hong-Hao Tu et al. (+1 more)

Non-Abelian anyons arise as exotic excitations in fractional quantum Hall (FQH) matter and have proved very elusive to realize in conventional platforms. In this work, we show that on a programmable quantum hardware platform, the more exotic FQH excitations are the less costly ones to prepare: clustered non-Abelian FQH states admit parallel quantum preparation circuits whose two-qubit depth is independent of system size, while constructing the more common Abelian Laughlin state requires a sequential circuit chain with linear depth. The centerpiece of this work is our new systematic framework for cataloging possible FQH states and preparing them on quantum circuits at unprecedented scale and variety. Our prepared parafermionic Read–Rezayi $\mathbb{Z}_3$ state holds depth 3 from 8 to 118 qubits, and full root sampling extends to a 154-qubit, 104-electron Read–Rezayi $\mathbb{Z}_4$ state. In all, our demonstrated 18-family catalog of prepared FQH states extends to all 156 qubits of an IBM Heron processor, limited only by existing hardware scale. Measurements on the prepared states recover the expected fractional quasihole charges, with the charge estimator exact in every symmetry-selected shot for the clustered states, and braiding data of the non-Abelian $e/4$ quasihole measured via interferometric extensions. Our work establishes a scalable route to studying FQH physics on quantum processors and opens new avenues for preparing and probing non-Abelian topological matter far beyond the reach of conventional platforms.
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All authors Cheng Xu, Ching Hua Lee, Hong-Hao Tu, Yang Zhang

Strongly Correlated Electrons · Cross-listed from hep-th

Generalized comodule tube algebras for boundary and domain wall defects of (2+1)D topological order

Zhian Jia and Sheng Tan

The tube algebra, which carries the structure of a $C^*$ weak Hopf algebra, is a fundamental tool for characterizing topological excitations in topological phases. In this work, we generalize the tube algebra framework to codimension-2 defects in $(2+1)$D gapped phases described by Turaev–Viro–Barrett–Westbury TQFTs, with particular emphasis on Levin–Wen string-net models. We show that such codimension-2 defects are described by a defect tube algebra, which naturally carries the structure of a comodule algebra over the weak Hopf tube algebra associated with the topological excitations. Boundary and domain wall defects are then characterized by the representations of the corresponding boundary and domain wall defect tube algebras. In particular, a domain wall defect tube algebra can be regarded as a generalized Drinfeld double of the tube algebras associated with the two adjacent boundary defects. More generally, for a domain wall joining $N$ bulk phases, the associated domain wall defect tube algebra can be viewed as an $N$-tuple algebra. This perspective extends naturally to general $k$-defects, namely codimension-2 defects joining $k$ codimension-1 defects, for which the resulting generalized tube algebra carries the structure of a multicomodule algebra.
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Strongly Correlated Electrons

Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2

Turgut Yilmaz, Anil Rajapitamahuni, Muhammad Awais Fiaz et al. (+7 more)

The mechanism driving the charge density wave (CDW) transition in TiSe2 has been debated for decades, with proposals ranging from an excitonic insulator to a lattice-driven instability. A central question remains whether the transition involves an opening or enhancement of the bulk band gap. Using high-resolution angle-resolved photoemission spectroscopy, we directly track the temperature evolution of the bulk band edges across the CDW transition at TCDW = 200 K. Contrary to the expectation of a gap-opening transition, we find that the size of the fundamental band gap remains constant from the high-temperature normal phase down to 160 K. While the CDW induces clear band-folding signatures and spectral weight redistribution, the underlying band extrema are unperturbed. These results demonstrate that TiSe2 does not undergo a temperature-driven electronic gap opening. Instead, they support a scenario where the transition is governed by a lattice symmetry-breaking reconstruction that folds, but does not gap, the electronic structure of a pre-existing band insulator.
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All authors Turgut Yilmaz, Anil Rajapitamahuni, Muhammad Awais Fiaz, Zhenxian Liu, Jerzy T. Sadowski, Abdullah Al-Mahboob, Asish K. Kundu, Shawna M. Hollen, Boris Sinkovic, Elio Vescovo

Strongly Correlated Electrons

Complex field-induced magnetic phases and anisotropic magnetotransport in off-stoichiometric CeCuBi2

Vikas Chahar, Shivam Rathod, Sneh et al. (+9 more)

We report a detailed study on the structural, angle-dependent magnetic and magnetotransport properties of highly anisotropic off-stoichiometric CeCuBi2 single crystals. Our results reveal CeCuBi2 as an anisotropic Kondo antiferromagnet exhibiting complex field-induced magnetic behavior and unusual magnetotransport properties. Magnetic susceptibility and specific heat measurements reveal antiferromagnetic (AFM) ordering below TN = 14 K with strong anisotropy and weak heavy-fermion behavior. Electrical transport measurements show highly anisotropic resistivity and a broad hump around 47 K, indicative of Kondo-driven heavy-fermion behavior. Magnetization measurements reveal multiple field-induced metamagnetic phases, while AC susceptibility measurements indicate slow spin dynamics and spin-glass-like behavior in intermediate field-induced magnetic states. Furthermore, we observe large and strongly anisotropic magneto transport responses, including room-temperature magnetoresistance of approximately 22% at 300 K and 9 T and butterfly-like anisotropic magnetoresistance with AMR values reaching approximately 10.9%. These results highlight a strong interplay among Kondo correlations, magnetic anisotropy, and field-tunable spin configurations, making CeCuBi2 a possible platform for exploring correlated and anisotropic quantum phenomena.
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All authors Vikas Chahar, Shivam Rathod, Sneh, Lipika, Shobha Singh, Balwant Singh Chauhan, Subhadeep Bej, Weida Yin, Yin-Chen Huang, Rie Y. Umetsu, Ratnamala Chatterjee, Kaustuv Manna