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Physics Condensed Matter Strongly Correlated Electrons

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Friday 21 August

Strongly Correlated Electrons

Electronic Toroidal Metals: Landau Theory and Magnetoelectric Fingerprints

Yuhang Xiao and Ning Hao

Toroidal order is a higher-rank multipolar order whose intrinsic realization in itinerant-electron systems remains unexplored. Here, we develop a generic theory of the electronic toroidal metal (ETM), in which toroidal order emerges spontaneously from electronic degrees of freedom near the Fermi surfaces. Because candidate toroidal bilinears can overlap by symmetry with the uniform charge current, we formulate a projected instability criterion that removes the noncondensable current component. Within this current-orthogonal sector, we identify a soft collective mode in the $\mathcal{P}$-odd and $\mathcal{T}$-odd particle-hole channel and demonstrate that ETM arises as a Fermi-liquid instability. We then define the toroidal moment in an itinerant system through the antisymmetric magnetoelectric response tensor. We further establish an intimate connection between this response and the topology of pseudospin texture: the rearrangement of pseudospin vortices changes the winding structure of the Fermi surfaces and markedly enhances the magnetoelectric response. ETM also exhibits characteristic nonlinear charge transport, including a pronounced enhancement of its interband quantum-geometric contribution. Our results establish ETM as a distinct metallic Landau phase and provide a general framework for understanding toroidal order generated by itinerant electrons.
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Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Quantum Wake Dynamics from Distinct Spectroscopic Perturbations

Umesh Kumar, Gonzalo Alvarez, David Alan Tennant et al. (+1 more)

Quantum wake dynamics in quantum magnets have recently been inferred from the dynamical spin structure factor, which probes only a restricted class of local perturbations. Here, we show that resonant inelastic x-ray scattering (RIXS) selection rules act as an operator filter on fractionalized excitations, producing distinct quantum wakes in the spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain. Using explicit real-time evolution of single-spin and spin-conserving bond correlators, we find that the conventional spin response propagates up to the maximum spinon velocity, $v_s=\frac{\pi}{2} J$, whereas the bond channels concentrate their spectral weight into a slower dominant wake with $v\simeq 0.92 J$, while weaker components remain bounded by the full spinon light cone. The corresponding momentum- and frequency-resolved responses map onto experimentally accessible RIXS channels, demonstrating that different spectroscopic perturbations resolve complementary pathways of many-body propagation beyond the neutron-scattering spin structure factor. Their inelastic spectral weights further provide access to quantum Fisher information, while equal-time bond sum rules connect the same spectroscopic channels to the ground-state energy. Because the same correlators can be prepared and measured on quantum hardware, they also define direct, experimentally anchored benchmarks for quantum simulations, particularly in frustrated and higher-dimensional magnets where controlled classical real-time calculations become challenging.
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All authors Umesh Kumar, Gonzalo Alvarez, David Alan Tennant, Satoshi Okamoto

Strongly Correlated Electrons

Distinguishing Mott and strain-induced anisotropic semimetals in magic-angle twisted bilayer graphene using Landau level spectroscopy

Keshav Singh, Juan Felipe Mendez-Valderrama, Erez Berg et al. (+2 more)

Recent quantum twisting microscopy experiments [1] have provided unprecedented momentum- and energy-resolved imaging of magic-angle twisted bilayer graphene, revealing a stark dichotomy between the heavy and light electronic characters of its narrow bands. In this work, we provide a sharp distinguishing criterion between the two most likely candidate states that exhibit spectroscopic features consistent with the experimental results. Focusing on charge neutrality, these states are 1) the 'Mott semimetal', governed by strong dynamical correlations, and 2) the 'strain-induced anisotropic semimetal', characterized by weak Hartree-Fock effects. We demonstrate that an out-of- plane magnetic field serves as a sharp discriminating probe based on the expected Landau level gap size hierarchy. We find that the strain-induced anisotropic semimetal has a robust gap hierarchy where the Chern C gaps, \Delta_C , decrease in order \Delta_{\pm 4} > \Delta_{\pm 8} > \Delta_{\pm 12}. In contrast, for the Mott semimetal, \Delta_{\pm 4} remains the largest gap, while the relative magnitude of the C = \pm 8, \pm 12 gaps depends sensitively on the applied magnetic field. We test the robustness of these results against strain orientation and lattice relaxation finding consistency between the gap hierarchy of the strained semimetal and previous incompressibility measurements at finite magnetic field [2].
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All authors Keshav Singh, Juan Felipe Mendez-Valderrama, Erez Berg, B. Andrei Bernevig, Oskar Vafek

Thursday 20 August

Strongly Correlated Electrons

Note on proliferation transitions of non-Abelian anyons

Meng Cheng

We study phase transitions out of a (2+1)d topological phase driven by the proliferation of anyons in a braided fusion subcategory. We describe a general theoretical framework for such transitions, in which the topological quantum field theory (TQFT) is coupled to dynamical matter associated with anyons in the subcategory. We interpret this construction using symmetry topological field theory (SymTFT), where the dynamics is localized on the symmetry boundary of the (3+1)d slab. We analyze several examples, and present explicit Chern-Simons-Higgs (CSH) field theories realizing the proliferation transitions. We also examine proliferation transitions that implement gauging of non-invertible one-form symmetry in the parent TQFT. This includes a general construction for ${\rm Rep}(G)$ one-form symmetry for a finite group $G$, and a CSH realization of the non-invertible one-form gauging ${\rm SU}(2)_{10}\rightarrow {\rm Spin}(5)_1$. We discuss which anyons proliferate at these transitions.
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Strongly Correlated Electrons · Cross-listed from hep-th

Maximal Total Quantum Dimension at Bounded Rank in WZW Modular Tensor Categories

Ce Shen

We determine the maximal torus topological entanglement entropy (TEE) at bounded torus ground-state degeneracy within simply connected untwisted Wess–Zumino–Witten theories. For a fixed modular tensor category $\mathcal C$, maximization over normalized torus ground states gives $\max_\psi\Gamma_{T^2}(\psi)=2\log{\mathcal D(\mathcal C)}$, attained in particular by the vacuum-flux state. The remaining problem is therefore to maximize total $\mathcal D$ at bounded categorical rank. For a simple WZW category $\mathcal C(\mathfrak g,k)$, write $r(\mathfrak g,k)$ and $\mathcal D(\mathfrak g,k)$ for its categorical rank and total quantum dimension, and define $F_{\WZW}(R)=\sup_{r(\mathfrak g,k)\leq R}2\log\mathcal D(\mathfrak g,k)$. We prove the sharp asymptotic law $\lim_{R\to\infty}\frac{F_{\WZW}(R)}{(\log_2R)^2} =\frac{7\zeta(3)}{4\pi^2}.$ The balanced symplectic sequence $Sp(2n)_n$ attains the coefficient. The constant arises from the odd Fourier modes of the type-$C$ root product at equal rank and level. A sharp entropy–spectral inequality, rank-level duality, and fixed-rank estimates give the global upper bound. A separate corollary extends the same leading law to semisimple WZW categories,equivalently finite Deligne products of simple factors. The unrestricted TQFT envelope remains open; the theorem is sharp within the stated WZW class and supplies a constructive lower bound for the general problem.
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Strongly Correlated Electrons

Torus Berry Data Determine All-Genus Abelian Topological Orders

Daniel Galviz

We show that for Abelian Chern-Simons topological orders, torus Berry matrices determine the all-genus extended TQFT. We identify the topological part of the projective Berry holonomy under metric deformations with the mapping-class-group representation of the Abelian Chern-Simons TQFT and prove that the normalized torus data reconstruct its finite quadratic module (G,q). Recent work showed that (G,q) classifies the extended theory up to symmetric monoidal natural isomorphism, and that the associated Abelian defect extension is determined by the pointed modular category C(G,q) arising from the same finite quadratic-module data. Therefore genus-one Berry data determine not only the all-genus bulk theory but also its associated defect structures without choosing a K-matrix presentation. We also prove that, for normalized character row errors $\delta$<21.96%, nearest-row decoding recovers the Abelian fusion algebra independently of the number of anyons. The result applies to Abelian fractional quantum Hall and spin-liquid phases described by even-lattice Chern-Simons theories.
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Strongly Correlated Electrons · Cross-listed from cond-mat.supr-con

Strange Metal Hall Effect in Underdoped BaFe$_2$(As$_{1-x}$P$_x$)$_2$

Augusto Ghiotto, Darian Hall, Yuanqi Lyu et al. (+7 more)

The unusual transport properties of strange metals point to the breakdown of the quasiparticle picture, the understanding of which remains one of the most vexing problems in physics. Here, we report investigations of the electrical Hall effect of the strange metal superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$. We show that a doping-independent contribution to the Hall effect exists within a fan shaped region above a putative quantum critical point. This `strange metal Hall' contribution echoes many of the properties of the antiferromangetic Hall response, but attains universal properties that distinguish it from the effects of Fermi surface reconstruction. This is consistent with an underlying origin connected to the presence of critical fluctuations, tying it to observations of $T$-linear resistivity and the appearance of unconventional superconductivity.
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All authors Augusto Ghiotto, Darian Hall, Yuanqi Lyu, Kohtaro Yamakawa, Sophie Rodehutskors, Corina Dunn, Philip J. W. Moll, John Singleton, Nikola Maksimovic, James G. Analytis

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

Signatures of a light-induced exciton condensate exhibiting BEC-BCS crossover

Khanh Duy Nguyen, Gabriele Berruto, Yunhe Bai et al. (+7 more)

Exciton condensates provide a platform to study quasiparticle pairing, Bose-Einstein condensation-Bardeen-Cooper-Schrieffer (BEC-BCS) crossover, and excitonic topological phenomena. Achieving a nonequilibrium exciton condensate allows the ultimate tunability of these emergent phenomena. Yet, evidence of a light-induced, nonequilibrium exciton condensate and its BEC-BCS crossover remains elusive. Here, we use time- and angle-resolved photoemission spectroscopy to demonstrate signatures of a non-equilibrium exciton condensate and its BEC-BCS crossover in monolayer MnBi2Te4. Following optical excitation, a distinctive hole-like dispersion representing excitons emerges and persists for >20 ps. Strikingly, energy-domain sharpening in the valence band occurs 2 ps after time zero and exhibits a sharp onset at a threshold pump fluence of 0.84 mJ/cm2. The delayed and strongly nonlinear response is difficult to reconcile with transient field effects or conventional carrier-induced band shifts but is consistent with a model of exciton condensation governed by a Berezinskii-Kosterlitz-Thouless transition. The estimated threshold exciton density agrees quantitatively with the Nelson-Kosterlitz critical density. At higher fluences, the exciton feature develops a camel-back-shaped dispersion, consistent with the BEC-BCS crossover in the condensate framework. Our work establishes ultrathin MnBi2Te4 as a model system for studying nonequilibrium exciton condensates with a connection to superconductivity and exciton-driven topological phases.
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All authors Khanh Duy Nguyen, Gabriele Berruto, Yunhe Bai, Thomas Marchese, Woojoo Lee, Haoran Lin, Jiangang Yang, Chong Liu, Y. Shirley Meng, Shuolong Yang

Strongly Correlated Electrons

Nonlinear Drude weight of the one-dimensional Hubbard model

Tetsuya Iwasaki and Hosho Katsura

We investigate nonlinear Drude weights (NLDWs) in the one-dimensional repulsive Hubbard model at zero temperature by combining exact Bethe-ansatz calculations with low-energy effective field theory. At quarter filling, we first derive the strong-coupling expansion of the NLDWs and confirm it numerically over a wide range of interaction strength. We then compare the numerical results with the prediction of the Tomonaga-Luttinger liquid (TLL) description including irrelevant perturbations. While band-curvature corrections yield finite contributions to higher-order NLDWs, the Umklapp interaction predicts divergent NLDWs when the order $n$ of the Drude weight exceeds a threshold determined by the TLL parameter. In contrast, finite-size scaling of the exact Bethe-ansatz results indicates that all calculated NLDWs remain finite in the thermodynamic limit, revealing a discrepancy between the exact results and the predictions of the low-energy effective field theory. At half filling, we analyze the finite-size scaling of the NLDWs across the Mott metal-insulator transition. We derive their asymptotic behavior in the insulating phase and propose a hyperscaling ansatz for NLDWs near the critical point, which is verified numerically. Our results clarify the interaction dependence and critical scaling of nonlinear transport coefficients in the one-dimensional Hubbard model and highlight limitations of the conventional low-energy effective description for higher-order transport.
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Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Learning Potts Models and $Z_3$ Toric Codes: Higher and Ordinary Nishimori Criticality

Rushikesh A. Patil, Malte Pütz, Rohit Mukherjee et al. (+3 more)

Motivated by a previous Ising study, we identify a ${\it higher}$ Nishimori line in the learning phase diagram of the $2D$ $q$-state Potts model $(2 < q\leq 4)$ under bond-energy measurements. This ${\it higher}$ Nishimori line meets the critical temperature line of the Potts model, in a ${\it higher}$ Nishimori critical point – a tricritical point at finite inference strength that separates a paramagnetic, a ferromagnetic and a 'spin-glass' phase. With analytical tools, we discuss the general structure of the rich phase diagram, which contains two unstable and three stable fixed points, and obtain a number of exact results for universal quantities, including the decay exponent of the Edwards-Anderson correlator, using a Gaussian measurement protocol which allows for exact calculations. Using extensive numerical tools, we confirm these statements for a generic, discrete $q$-state measurement protocol and determine precise numerical estimates for the location of higher and ordinary Nishimori critical points as well as RG flows between the various fixed points. We also discuss the Casimir effective central charges of the critical points in the learning phase diagram, and their monotonic ${\it decrease}$ along measurement-induced RG flows, as established non-perturbatively by the c-effective theorem and its extensions, and contrast it to the monotonic increase along the corresponding RG flows in the random-bond Potts model. Finally, we discuss a general argument based on ${\it Elitzur's \; theorem}$ that establishes stability of the ordinary Nishimori critical points in their respective learning phase diagrams. Equivalently, our results describe a monitored deformed $\mathbb{Z}_q$ toric code where the tricritical ${\it higher}$ Nishimori point is an 'information' critical point that separates stable quantum, classical, and no memory phases.
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All authors Rushikesh A. Patil, Malte Pütz, Rohit Mukherjee, Guo-Yi Zhu, Simon Trebst, Andreas W. W. Ludwig

Strongly Correlated Electrons

Universal meson spectra near $(1+1)$-dimensional Ising criticality

Xiao Wang and Jianda Wu

Near $(1+1)$-dimensional [$(1+1)$D] Ising criticality, a magnetic perturbation induces confinement and produces a cascade of bound-state excitations known as mesons. Here we show these mesons share a universal mass scaling after independently rescaling the model-dependent microscopic couplings. The number of stable mesons is controlled by the lightest two-meson threshold, while the lightest-meson mass follows a continuous trajectory characterized by a single scaling parameter. Using Hamiltonian truncation method, we obtain the trajectory numerically in both Ising field theory and the near-critical mixed-field Ising chain (MFIC). Under the rescaling, the trajectory and stable-meson-count crossover windows of MFIC both collapse onto the field-theory results. To further demonstrate the above universal organization of the meson spectra, we consider a class of four-periodic spin-$1/2$ Heisenberg-Ising chains under transverse fields, whose parameter space contains a family of quantum Ising critical points. The Hamiltonian family includes effective spin models for the quasi-one-dimensional antiferromagnets Ba(Sr)Co$_2$V$_2$O$_8$. Using tensor-network calculations, we obtain the corresponding lightest-meson mass trajectory for BaCo$_2$V$_2$O$_8$ and find that it also collapse onto the same universal curve given by field-theory result. Our results suggest that the universal scaling structure of quantum Ising criticality extends into the nearby confining regime, governing the organization of the meson spectrum. They thereby provide a practical criterion for interpreting excitations of quasi-1D Ising-like magnets in mixed fields beyond $E_8$ integrability.
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Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Biorthogonal Conformal Dynamics in Non-Hermitian Quantum Quenches

Yifan Liu

Global quenches at one-dimensional critical points admit a boundary conformal field theory (BCFT) description in which Euclidean strip correlators are analytically continued to real time. We formulate this construction for interacting non-Hermitian critical systems, where a right ket alone does not specify the dynamical readout and the left covector is part of the microscopic quench protocol. Independent left and right preparations flowing to the same conformal boundary define the two temporal boundaries of a strip with generally complex one-sided extrapolation parameters; linear and antilinear symmetry pairings are exploited to constrain this geometry. In the interacting Yang-Lee spin chain, statically calibrated boundary data determine the biorthogonal dynamics of the complete-character return amplitude, a primary one-point function, and a spatial correlator. The imaginary part of the linear-paired extrapolation parameter predicts the temporal center of an independently evolved antilinear-paired one-point function at the $10^{-3}$ relative level; the same preparation phase controls local phase evolution and the analytic-continuation path of boundary blocks. Further results test this formalism with a direct field-on quench, mixed left and right preparations, and a complex five-state Potts fixed point with complex primary dimensions. These results establish a BCFT framework for biorthogonal global quenches in interacting non-Hermitian critical systems, in which complex temporal-boundary data organize universal post-quench dynamics.
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Strongly Correlated Electrons · Cross-listed from quant-ph

The ebbs and flows of quantum learning and sensing

Matias Karjula, Teemu Ojanen, Tapio Ala-Nissila et al. (+1 more)

What is the relation between subsystem quantum complexity and the emergence of computationally useful structure? We address this by studying a family of minimally tunable postvariational quantum circuits, and show how spectral nonflatness and metrological response directly control the ensemble-typical information processing power. This unveils an intermediate "learning phase" that precedes the onset of quantum chaos, characterized by pronounced nonflatness and sensitivity of readout states. The optimal information processing capacity improves with system size, while deep scrambling suppresses observable response. The results reveal how such features of random quantum dynamics can be viewed as computational resources for scalable nonlinear computation.
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All authors Matias Karjula, Teemu Ojanen, Tapio Ala-Nissila, Moein N. Ivaki

Strongly Correlated Electrons · Cross-listed from quant-ph

Reinforcement Learning to Harness Approximation Errors for Long-Time Quantum Simulation

Yu-Bo Shi, Markus Heyl, Roderich Moessner et al. (+2 more)

Accurate digital quantum simulation at long times is limited by the accumulation of errors inherent to approximate simulation. Here we introduce RL-Trotter, a reinforcement-learning framework that treats unavoidable approximation errors as resources for error correction rather than merely imperfections to suppress. We show that low-dimensional information from conservation laws, such as the energy and energy variance, provides a sufficient learning signal to guide the agent, which learns to adapt a single scalar—the next Trotter step size—without access to the target wave function. By optimizing the entire long-time evolution rather than individual steps, RL-Trotter discovers self-correcting sequences in which later errors compensate for those accumulated earlier, increasing the accuracy of the long-time dynamics. The learned policies are intrinsically robust to measurement noise, substantially reducing measurement overhead. They also generalize to previously unseen, physically similar initial states and transfer from small, classically simulable systems to systems an order of magnitude larger. This enables a practical protocol based on classical pretraining followed by direct deployment or limited fine-tuning on quantum hardware. Our results establish a broader perspective for quantum algorithms: errors in approximate evolution can be orchestrated into resources for accurate and resource-efficient quantum dynamics.
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All authors Yu-Bo Shi, Markus Heyl, Roderich Moessner, Marin Bukov, Hongzheng Zhao

Strongly Correlated Electrons · Cross-listed from cond-mat.quant-gas

Structural complexity of an SU(3) Fermi Hubbard model

Jiani Fu, Zewen Zhang and Eduardo Ibarra-García-Padilla

Two-dimensional quantum gas microscopy provides an unparalleled tool to study quantum many-body systems using ultracold atoms. For the SU(2) Fermi Hubbard model (FHM), access to spin-resolved projective measurements has been vital for quantifying correlation functions and mapping out the phase diagram. Recent progress in quantum gas microscopy for experiments with ultracold alkaline-earth atoms, which are well described by the SU(N) FHM and are predicted to host exotic ground-state phases, calls for the development of theory-free numerical techniques to extract physical information from their projective measurements. To that end, we evaluate the multiscale structural complexity of snapshots of an SU(3) FHM in the square lattice at $1/3$-filling. We employ mean-field theory to generate spin-resolved density distributions and compute their structural complexity using rectangular coarse-graining windows. We demonstrate that these complexities are linked to relevant physical observables such as the entanglement entropy, and are extremely sensitive for locating phase boundaries. The results presented here validate the structural complexity as an efficient and reliable tool for analyzing the outputs of SU(N) quantum gas microscopes, offering a theory-free property, immediately accessible to experiments.
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Strongly Correlated Electrons

Pressure-tuning of electronic structure of CeTe3 probed by femtosecond collective mode spectroscopy

Chandra V. Kotyada, Priyanka Yogi, Amon P. Lanz et al. (+8 more)

We use femtosecond optical spectroscopy to study the evolution of coherent order-parameter dynamics in the prototypical charge-density-wave (CDW) system CeTe3 under hydrostatic pressure. The CDW transition temperature decreases from approximately 570 K at ambient pressure to near room temperature at approximately 6 GPa. The pressure dependence of the order-parameter recovery dynamics indicates enhanced electron-phonon coupling with increasing pressure, implying that CDW suppression is driven predominantly by the reduction in Fermi-surface nesting. Above 7 GPa, no evidence of CDW order is observed down to cryogenic temperatures. Concurrently, the relaxation dynamics exhibit significant slowing down at low-temperatures, consistent with emerging heavy-electron behaviour due to pressure-enhanced hybridization between localized Ce 4f levels and itinerant carriers.
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All authors Chandra V. Kotyada, Priyanka Yogi, Amon P. Lanz, Rolf Heid, Jonas Tauch, Manuel Obergfell, Hanjo Schaefer, Paula Giraldo-Gallo, Ian R. Fisher, Alexej Pashkin, Jure Demsar

Strongly Correlated Electrons

Volatile resistive-switched state in a bulk organic conductor with a sharp metal-insulator transition

Riku Ishii, Ryo Motohashi, Keitaro Tada et al. (+6 more)

Volatile resistive switching in correlated-electron systems, characterized by an abrupt resistance decrease under applied current, is crucial for developing next-generation electronics. Despite its technological significance, the underlying physics remains elusive. Inorganic thin films on substrates—the widely studied platform for resistive switching—usually exhibit broad temperature-induced metal-insulator transitions (MITs) and substantial heat dissipation. These factors complicate the nonlinear thermal effect induced by Joule heating, a key contributor to resistive switching, rendering it excessively complex and difficult to decipher. Here we investigate a resistive-switched state in the bulk organic conductor ($d$7-DMe-DCNQI)$_{2}$Cu, which undergoes an extremely sharp first-order MIT and exhibits weak heat dissipation, using resistance and $^{1}$H-NMR measurements. These extreme conditions make the Joule heating effect vivid, allowing us to observe peculiar phenomena, including temperature locking to the MIT and `inverse Ohm's law'—an inverse proportionality between voltage and current. These findings provide fundamental insights into the nonlinear thermal effect in resistive switching, offering a pathway to efficient resistive-switching technologies.
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All authors Riku Ishii, Ryo Motohashi, Keitaro Tada, Yusuke Suzuki, Takayoshi Kouchi, Hiroshi Oike, Fumitaka Kagawa, Reizo Kato, Tetsuaki Itou

Strongly Correlated Electrons

Tilted $p$-wave magnet candidate CeNiAsO

Zhuo Wang, Zheng Liu, Shuo Zou et al. (+17 more)

The unexpectedly small ordered moments of CeNiAsO, a candidate for correlated $p$-wave magnet, have posed a serious challenge to the precise determination of its magnetic structure, hindering the understanding of its fundamental properties. By leveraging the high sensitivity to local internal fields, our $^{75}$As nuclear quadrupole / magnetic resonance experiments reveal a commensurate antiferromagnetic order with a small out-of-plane moment $m_z\approx0.05$ $\mu_{\mathrm{B}}$. This tilted magnetic configuration not only rotates the spin polarization axis away from the crystallographic $\mathbf{c}$-axis, but also enhances the non-relativistic spin splitting. We refer to this rare paradigm as a \textit{tilted $p$-wave magnet}.
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All authors Zhuo Wang, Zheng Liu, Shuo Zou, Hua-Xun Li, Jin-Xin Hu, Zhuolun Qiu, Ze Wang, Jiamin Gong, Lucheng Wei, Kangjian Luo, Hai Zeng, Meng Zhang, Chao Dong, Chuanyin Xi, Junfeng Wang, Jiakun Fang, Xiaotao Han, Guang-Han Cao, Liang Li, Yongkang Luo

Strongly Correlated Electrons · Cross-listed from math-ph

Moore–Read construction and explicit monodromies of Laughlin states on Riemann surfaces

Kiyoon Eum

We revisit the Moore–Read construction of the $\nu=1/k$ Laughlin states on compact Riemann surfaces, deriving their conformal blocks from $U(1)_k$ Chern–Simons theory through the CS/WZW correspondence. We compute their explicit monodromies under quasi-hole transport and Aharonov–Bohm flux insertion, and conjecture that these coincide with the corresponding adiabatic holonomies. Under this identification, we recover classical results on Laughlin states including the flux-averaged Hall conductance $1/k$ via a vector bundle of Laughlin states over $Jac(\Sigma)$. We also relate our construction to the recently developed algebro-geometric approach to higher genus Laughlin states.
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Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Exact partition function of arithmetic Ising model

Anu Dhochak, Ken Kikuchi and Shrinit Singh

We present a compact formula for the exact partition function of the $d$-dimensional arithmetic Ising model (AIM). For a $2\times2$ system, we express it analytically using the $q$-Hurwitz-Lerch zeta function and derive explicit forms for the free energy and entropy. Additionally, we find that the entropy increases at high temperatures, supporting the presence of entropic order.
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Strongly Correlated Electrons

Universality of long-wavelength behavior of composite-fermion Fermi liquid

Aamir A. Makki, Mytraya Gattu and J. K. Jain

A recent article evaluated the long-wavelength behavior of the projected static structure factor of the composite-fermion (CF) liquid within the zeroth-order microscopic theory and found $\bar{S}(\mathbf{q})\sim q^3$, in disagreement with the $\bar{S}(\mathbf{q})\sim q^3\ln q$ behavior predicted by the Chern-Simons field theory for the Coulomb interaction. Here we consider the possibility that the discrepancy arises because the zeroth-order CF Fermi-liquid wave function used in that work does not properly capture the long wavelength behavior. We use CF diagonalization to significantly improve the wave function but do not find any evidence for $\bar{S}(\mathbf{q})\sim q^3 \ln q$ behavior. Additionally, we find that the small-$q$ behavior of $\bar{S}(\mathbf{q})$ is also insensitive to the form of the interaction between electrons, suggesting universality.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Beyond Integrability Preserving Renormalization-Group Protocol in Non-Hermitian Hamiltonians with Time-Dependent Interaction Strengths

Parameshwar R. Pasnoori

It is well established that in time-dependent quantum systems, integrability preserving time-dependent interaction strengths are identical to the renormalization group (RG) trajectories of the corresponding static model when time `$t$' in the driven model is identified with the logarithm of the cutoff `$\log\Lambda$' of the static model. We refer to this integrability preserving driving as the RG protocol. In this work we extend the class of time-dependent integrable models to include non-Hermitian quantum models with time-dependent interaction strengths. Using the recently formulated generalized Bethe ansatz framework [P. R. Pasnoori, Phys. Rev. B 112, L060409 (2025)], we show that the constraints imposed by integrability are more general: The interaction strengths of the static model that flow in the RG follow the respective RG trajectories in the corresponding time-dependent model as described above. In addition, the interaction strengths of the static model that are RG invariant can either be constant or have a specific time-dependence in the corresponding time-dependent model which is constrained by integrability. Thus we establish that in the context of time-dependent non-Hermitian systems, the set of integrability preserving time-dependent strengths is larger than the set corresponding to the RG protocol.
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Wednesday 19 August

Strongly Correlated Electrons

Reply to Comment on: Microscopic signatures of an imaginary charge density wave in a kagome metal

S. Suetsugu, S. Kitagawa, K. Ishida et al. (+2 more)

We address a recent Comment [I. Nikolov et al., arXiv:2608.13579 (2026)] proposing crystalline mosaicity as an alternative explanation for the asymmetric nuclear magnetic resonance (NMR) spectra reported in our study [S. Suetsugu et al., Nat. Phys. 22, 1251–1256 (2026)]. We show that this scenario requires substantial temperature- and site-dependent distributions of crystallographic orientations and additional site-dependent distributions of the electric field gradient (EFG) asymmetry parameter, none of which follow from ordinary crystalline mosaicity. We therefore conclude that crystalline mosaicity cannot account for the observed site-selective spectral asymmetry and does not provide an alternative explanation for the central spectroscopic observation underlying our interpretation.
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All authors S. Suetsugu, S. Kitagawa, K. Ishida, T. Shibauchi, Y. Matsuda

Strongly Correlated Electrons

Antiferromagnetic order and lattice response in DyCuAs$_2$

M. G. Kim, J.-W. Kim, P. Ryan et al. (+2 more)

We report high-resolution synchrotron X-ray diffraction and X-ray resonant magnetic scattering (XRMS) studies of the low-temperature crystal and magnetic structures of DyCuAs$_2$, a member of the \RE{}CuAs$_2$ family exhibiting a resistivity minimum above the antiferromagnetic transition temperature. Synchrotron diffraction measurements reveal that DyCuAs$_2$ preserves tetragonal symmetry down to low temperature within the experimental resolution, although pronounced anomalies in both lattice parameters $a$ and $c$ are observed near the antiferromagnetic transition temperature, $T_{\mathrm N}\approx7$~K, indicating strong magnetoelastic coupling. XRMS measurements at the Dy $L_3$ edge establish commensurate antiferromagnetic ordering below $T_{\mathrm N}$ with AFM Bragg peaks at \qq{} = (0, 0, 0.5). Representation analysis and calculations of the AFM Bragg peak intensities identify the magnetic structure as the $\Gamma_{10}$ representation, consisting of in-plane Dy moments stacked along the \cc{} axis in a $++--$ sequence. The magnetic structure is therefore identical to that previously reported for SmCuAs$_2$. Comparison among DyCuAs$_2$, SmCuAs$_2$, and GdCuAs$_2$ suggests that in-plane AFM order and the associated magnetic frustration on the tetragonal lattice are closely connected to the emergence of the resistivity minimum in the \RE{}CuAs$_2$ family. At the same time, the enhanced lattice response and stronger magnetic-field sensitivity observed in DyCuAs$_2$ imply that magnetoelastic and spin-orbit interactions additionally play important roles in determining the robustness of this anomalous transport behavior.
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All authors M. G. Kim, J.-W. Kim, P. Ryan, D. Evans, E. D. Mun

Strongly Correlated Electrons

Tunable inter-bilayer magnetic correlations and candidate multipolar physics in the van der Waals oxyhalides DyOCl, DyOBr, and DyOI

F. C. Brooks, X. Bai, J. Bacsa et al. (+5 more)

Rare-earth van der Waals magnets provide a route to combining strong spin-orbit coupling, large magnetic moments, and reduced dimensionality in bulk crystals. We report a comparative study of the dysprosium oxyhalides DyOX (X = Cl, Br, I), which realize square-bilayer networks of Dy3+ moments separated by a tunable van der Waals gap. Structural refinements show that increasing the halide ionic radius strongly expands the inter-bilayer spacing while leaving the local bilayer geometry nearly unchanged. Magnetization and heat-capacity measurements reveal two low-temperature anomalies in all three compounds: antiferromagnetic order at TN ~ 7-10 K and a broader anomaly near TQ ~ 27-30 K. Single-crystal magnetization on DyOCl and DyOBr establishes a strong hard-c-axis anisotropy, consistent with crystal-field analysis of DyOCl, which yields an XY-like ground-state g tensor. Neutron diffraction shows long-range antiferromagnetic order in DyOCl, whereas DyOBr and DyOI exhibit sharp magnetic scattering coexisting with Warren-like diffuse features, consistent with robust in-plane correlations and imperfect inter-bilayer registry. Inelastic neutron scattering on DyOCl identifies crystal-field excitations near 25-30 meV and an additional magnetic mode near 10 meV whose temperature dependence is tied to the high-temperature anomaly. Taken together, these results establish DyOX as a tunable family of quasi-two-dimensional rare-earth magnets and point to candidate multipolar physics associated with low-lying crystal-field states. Direct probes of quadrupolar order, such as resonant x-ray scattering or elastic-constant measurements, will be required to determine the order parameter at TQ.
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All authors F. C. Brooks, X. Bai, J. Bacsa, V. O. Garlea, S. Calder, N. Butch, M. B. Stone, M. Mourigal

Strongly Correlated Electrons

Hysteresis without coexistence: disorder-rounded first-order transitions in a van der Waals magnet

Xiaoyu Guo, Abby N. Neill, Christopher M. Pasco et al. (+2 more)

Quenched disorder can profoundly modify phase transitions. In low-dimensional systems, theory predicts that even weak quenched disorder can round the thermodynamic discontinuities associated with a first-order phase transition. Here, we employ time-domain terahertz spectroscopy to investigate the quasi-two-dimensional trimerized kagome van der Waals magnet family Nb$_3$Cl$_{8-x}$Br$_x$ ($x=0$, 1 and 8). We observe the emergence of an additional phonon branch upon Br substitution, whose spectral weight increases and frequency softens with increasing Br concentration. The temperature evolution of the phonon frequencies reveals a clean first-order transition in Nb$_3$Cl$_8$ characterized by macroscopic phase coexistence and thermal hysteresis. In contrast, the transition in the substitutionally disordered compound Nb$_3$Cl$_7$Br retains its hysteresis while exhibiting a substantially broadened transition with no resolvable macroscopic phase coexistence. These observations reveal disorder-induced fragmentation of the transition into locally favored domains instead of well-defined bulk phases separated by stable phase boundaries. The behavior is consistent with the Imry-Wortis and the Aizenman-Wehr scenarios for the effect of quenched disorder in low-dimensional systems, which destabilizes macroscopic phase coexistence and rounds the thermodynamic discontinuities associated with first-order transitions. Thermal hysteresis persists in the disordered compound despite the lack of resolvable coexistence, indicating that the two features often treated as a single hallmark of first-order character arise distinctly and can be separated by disorder. Moreover, our results establish Nb$_3$Cl$_{8-x}$Br$_x$ as a promising platform for investigating the effects of disorder on first-order transitions in low-dimensional systems.
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All authors Xiaoyu Guo, Abby N. Neill, Christopher M. Pasco, Tyrel M. McQueen, N. P. Armitage

Strongly Correlated Electrons · Cross-listed from quant-ph

Statistical Mechanics of Non-Abelian Learnability Transitions

Ruochen Ma and Romain Vasseur

Monitored many-body quantum systems can undergo sharp learnability transitions characterized by how much information can be learned by the observer. When the dynamics conserves a non-Abelian charge, such as an $SU(2)$ spin, understanding how the observer learns the total charge remains an outstanding problem. Unlike the Abelian case, where charge measurements on distinct sites commute, the $SU(2)$-symmetric readouts are noncommuting fusion measurements, making learning a genuinely quantum inference problem. In this work, we propose a theory of $1+1d$ monitored quantum dynamics with $SU(2)$ symmetry, and show that it can be described by an effective replicated loop model comprised of a replica-pairing field and a diffusive ($z=2$) background sector that carries the $SU(2)$ charge and remains gapless throughout the phase diagram. Our theory predicts that the "spin-sharpening” and entanglement transitions coincide as a single transition. Ordering of the pairing field produces volume-law entanglement and hides the background sector from measurements, leading to a learning time of $t\sim L^{3}$ for the total spin. When the pairing field disorders, the background sector alone gives logarithmic entanglement and a diffusive learning time $t\sim L^{2}$. Our analysis is controlled by a large-loop-fugacity expansion.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Simulating Black Hole Thermality and Interior Scrambling on a Superconducting Quantum Processor

Ryan Smith, Ewan Forbes, Iason A. Sofos et al. (+2 more)

We implement a chiral spin-chain black hole simulator on IBM superconducting quantum hardware and probe, within a common microscopic framework, both semiclassical horizon physics and interacting quantum scrambling. We first measure the dispersion relation across the exterior, horizon and over-tilted interior regimes, reproducing the predicted evolution of the effective light-cone structure. To probe Hawking thermality, we prepare a localised excitation inside the horizon and monitor its density response at an exterior site, observing the predicted inverse relation between the peak arrival time and the surface gravity, thereby establishing a calibrated dynamical estimator of the Hawking temperature. Beyond the semiclassical regime, we continuously tune the interactions and distinguish non-exponential operator spreading in the free-fermion limit from Lyapunov-like OTOC decay in the strongly interacting chiral regime. These measurements use observable-specific Floquet circuits derived from the same parent chiral model, including its mean-field and coordinate-equivalent XY descriptions, to reduce circuit depth while preserving the physics relevant to each probe. Our results provide a unified programmable platform for studying horizon geometry, Hawking thermality and interacting scrambling on quantum hardware.
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All authors Ryan Smith, Ewan Forbes, Iason A. Sofos, Andrew Hallam, Jiannis K. Pachos

Strongly Correlated Electrons · Cross-listed from quant-ph

Thermal Throttling of Quantum State Transfer

Twesh Upadhyaya, T. C. Mooney, Yifan Hong et al. (+1 more)

Quantum state transfer on qubit lattices is a crucial step in a panoply of quantum information processing tasks. Understanding its fundamental limits in the presence of practical imperfections remains a pressing open question. In particular, it is unclear how thermal noise in the intermediate ancilla sites impedes transfer. In this work, we derive tight lower bounds on the necessary growth of commutator norms to achieve approximate state transfer. Specializing to 1D power-law systems with thermal ancilla states, we demonstrate that state transfer runtimes depend sensitively on the scaling of temperature with system size, improving logarithmic bounds to algebraic ones. Our work extends previous results on exact state transfer to the qualitatively different and more practically relevant regime of approximate state transfer.
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All authors Twesh Upadhyaya, T. C. Mooney, Yifan Hong, Alexey V. Gorshkov

Strongly Correlated Electrons

Interferometric Signatures of Zero Modes in Fractional Quantum Hall-Superconductor Heterostructures

Junyi Cao, Ramanjit Sohal, Angela Kou et al. (+1 more)

Fractional quantum Hall-superconductor (FQH-SC) heterostructures are predicted to host defect-bound parafermion zero modes (PZMs). We propose two related configurations to probe their fusion structure. In a Josephson junction coupled to a single quantum point contact (QPC), quasiparticle tunneling switches the defect fusion channel, producing stochastic transitions between branches of the fractional Josephson spectrum. Embedding the junction in a two-QPC Fabry-Pérot interferometer provides a complementary probe. Weak zero mode tunneling produces fusion-channel-dependent interference while strong tunneling makes the interferometer probe a superposition of fusion channels and strongly suppresses the signal: in the topological limit it vanishes exactly, revealing the defects' non-Abelian nature even when the parent FQH state is Abelian.
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All authors Junyi Cao, Ramanjit Sohal, Angela Kou, Eduardo Fradkin