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Physics Condensed Matter Strongly Correlated Electrons

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Thursday 27 August

Strongly Correlated Electrons · Cross-listed from math-ph

2-Morita Theory of $E_2$-Algebras and Module Categories

Rongge Xu and Holiverse Yang

Building on our previous work on 2-Morita equivalence for $E_2$-algebras using topological pictures, we develop a systematic framework for Morita equivalence of topological orders in different dimensions in terms of $n$-Morita categories $\mathrm{Mrt}_{E_n}(\mathcal{C})$. In this framework, various notions of $n$-Morita equivalence are unified as equivalences of objects in $\mathrm{Mrt}_{E_n}(\mathcal{C})$. We also compare the constructions of higher Morita categories due to Haugseng and to Gwilliam–Scheimbauer. For $n=1,2$, we prove that the functor $\mathrm{Mod}_n:\mathrm{Mrt}_{E_n}(\mathcal{C})\to \mathrm{Mrt}_{E_{n-1}}(\mathrm{LMod}^{\mathrm{rep}}(\mathcal{C}))$ is an equivalence, relating the algebraic description of higher Morita theory to its realization in terms of module categories. In this formulation, the notion of a bi-bimodule arises naturally and provides a common framework for local and confined modules. Its explicit orientation data, together with the corresponding fusion rules, clarifies the relations among defects arising from condensation in topological orders.
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Strongly Correlated Electrons

Multi-orbital physics in inverse Lieb lattice altermagnets

Mercè Roig, Jannik Gondolf, Andreas Kreisel et al. (+2 more)

The inverse Lieb lattice has recently emerged as a promising platform for altermagnetism, with several materials with this structure proposed as $d$-wave altermagnetic candidates. Here, we develop a symmetry-based microscopic Hamiltonian for these materials that includes both sublattice and orbital degrees of freedom, going beyond the sublattice-only minimal models that have been extensively used to study such altermagnets. We apply these models to examine multi-orbital electron correlation physics in the vanadium oxychalcogenide family altermagnets, which contain dominant $xy$ and $xz/yz$ orbitals character at the Fermi level in the altermagnetic state. We demonstrate that $xy$ orbitals are crucial to stabilize the altermagnetic state observed within a single V$_2$O layer, and altermagnetic order in the $xz/yz$ orbitals is induced through Hund's coupling. Additionally, we show that these multi-orbital models reveal topological regimes in which topological edge states are naturally orbital selective.
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All authors Mercè Roig, Jannik Gondolf, Andreas Kreisel, Brian M. Andersen, Daniel F. Agterberg

Strongly Correlated Electrons

3D- (H-theta-phi) magnetic phase diagram of antiferromagnetic metal GdB6 with electron and lattice instability

A. N. Azarevich, A. V. Bogach, T. F. Garipova et al. (+10 more)

The origin of charge transport and magnetization anisotropy was studied in GdB6, an antiferromagnetic (AF) metal (Néel temperature TN ~ 15.5 K) with cubic lattice and Gd S-type magnetic ions. Both small static Jahn-Teller distortions and nanoscale electronic instabilities (dynamic charge stripes) were found in precise low temperature X-ray diffraction measurements. The detailed magnetic field (H) vs temperature (T) phase diagrams were constructed with two main magnetic phases AF(I) and AF(II). Using the angular phi-dependences of magnetoresistance and magnetization, impeller-type patterns of the H-phi magnetic phase diagrams in the (110) and (111) planes were found at helium temperatures, which included the AF phases I and II separated from each other by radial and circular boundaries. The results argue in favor of the important role of the spin density wave 5d- component in the magnetic structure of AF(II) state. Charge fluctuations in stripes are proposed to be responsible for the suppression of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) indirect exchange between the first and second neighboring Gd3+ ions located along the <100> and <110> directions. These dynamic charge stripes and vibrationally coupled Gd-Gd pairs produce unusual anisotropy of charge scattering and the impeller-type diagrams in GdB6 with S-type magnetic ion.
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All authors A. N. Azarevich, A. V. Bogach, T. F. Garipova, V. V. Voronov, M. Rajnak, S. Gabani, K. Flachbart, N. B. Bolotina, O. N. Khrykina, V. M. Gridchina, A. Yu. Tsvetkov, S. Yu. Gavrilkin, N. E. Sluchanko

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

Decoupled domain-texture switching from magnetic easy axis in kagome ferromagnet EuTi3Bi4

Yunhao Wang, Shiyu Zhu, Guohao Xi et al. (+13 more)

Magnetic anisotropy defines the easy axis of a magnetic material and governs the spatial arrangement of its domains. To date, anisotropy engineering has focused on reorienting the easy axis or tuning the anisotropy energy, both of which demand substantial energy input. Here, we demonstrate that magnetic domain textures can be switched without reorienting the easy axis, as observed in a kagome ferromagnet EuTi3Bi4 crystal. Using low-temperature magnetic force microscopy, we observe that the preferred orientation of magnetic domains switches from the a-axis to the b-axis upon temperature variation, and that this switching can also be triggered by an out-of-plane magnetic-field reset. Magnetization measurements and density functional theory calculations confirm a robust c-axis easy magnetization, ruling out a conventional spin-reorientation transition. Instead, the texture switching is governed by the temperature dependence of the in-plane variation of the Magnetic anisotropy energy landscape, which arises from two competing interactions with different decay rates: single-ion anisotropy favors a-oriented spin components, while nearest-neighbor anisotropic exchange favors b-oriented ones. Furthermore, the critical switching temperature is substantially elevated in a mechanically exfoliated EuTi3Bi4 flake. Our findings establish that macroscopic magnetic textures can be effectively manipulated by tuning the competition between in-plane anisotropic interactions, without the energy cost of reorienting the easy axis.
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All authors Yunhao Wang, Shiyu Zhu, Guohao Xi, Runnong Zhou, Ruwen Wang, Jianfeng Guo, Jiali Liu, Zichao Chen, Kailin Xu, Cong Wang, Chengmin Shen, Jiang Xiao, Haitao Yang, Xiaoli Dong, Wei Ji, Hong-Jun Gao

Strongly Correlated Electrons

Interlayer-engineering of Charge Order Wave Vector in Kagome Metals

Muntafa M. Mahi, Quazi D. M. Khosru, M. Zahid Hasan et al. (+2 more)

Charge orders in the kagome metals AV$_3$Sb$_5$ sit at the center of a rich phase diagram that also includes superconductivity, nematicity, and signatures of time-reversal-symmetry breaking. Yet even the basic question of which charge ordering wave vectors are intrinsic, and which are selected by dimensionality and lattice coupling, remains unsettled. Importantly, the microscopic origin of different charge orders and, in particular, the relationship between the robust bulk $2 \times 2$ charge order and the controversial $4 \times 1$ modulation, which is primarily resolved by surface probes, remains unresolved. Here, we use first-principles calculations to study the role of interlayer coupling in CsV$_3$Sb$_5$ by tuning the interlayer separation from the monolayer limit to the bulk limit. In the monolayer AV$_3$Sb$_5$ (A = Rb, Cs), the phonon spectrum exhibits no instability at the M point; instead, the dominant lattice instability occurs at q = (1/4, 0, 0), consistent with a $4 \times 1$ modulation. As interlayer coupling increases in CsV$_3$Sb$_5$, an M-point phonon progressively softens and becomes unstable already near c = 12.24 Å, evolving into the strong $2 \times 2$ instability characteristic of the bulk. These results identify interlayer coupling as a control parameter at a fixed stoichiometry that links competing $4 \times 1$ and $2 \times 2$ tendencies, providing a unified framework for understanding why multiple charge-order wave vectors coexist and compete in kagome metals.
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All authors Muntafa M. Mahi, Quazi D. M. Khosru, M. Zahid Hasan, Mahbub Alam, Md Shafayat Hossain

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

Strain-driven orbital-selective reconstruction and bicollinear-to-stripe evolution in FeTe

Zhenfeng Ouyang, Yin Chen, Yi-Heng Tian et al. (+4 more)

FeTe, as a representative parent material among iron-based superconductors, provides an ideal platform for exploring the interplay among orbital-selective correlations, magnetism, and unconventional superconductivity. However, a unified picture of the correlated electronic structure and magnetism of FeTe under strain remains to be fully clarified. Here, combining density functional theory plus dynamical mean-field theory and Heisenberg model analysis, we uncover an orbital-selective reconstruction of the correlated electronic structure and reveal a strain-driven trajectory from bicollinear to stripe antiferromagnetism (AFM) via an intermediate competing staggered $n$-mer AFM regime in FeTe. Moderate strain gives rise to a regime where more coherent quasiparticles coexist with suppressed local moments. Further strain drives FeTe into an incoherent correlated regime with robust local moments and Fe-$3d_{z^2}$-dominated low-energy states. These results establish a strain-driven trajectory across distinct magnetic and correlated electronic states in FeTe.
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All authors Zhenfeng Ouyang, Yin Chen, Yi-Heng Tian, Jia-Ming Wang, Rong-Qiang He, Kai Liu, Zhong-Yi Lu

Strongly Correlated Electrons

Thermally quenched metastability in metal-insulator transitions via elemental substitution

Hiroshi Oike, Yasunori Takahashi, Keisuke Shibuya et al. (+5 more)

Thermal quenching inhibits equilibration toward the thermodynamic ground state during phase transitions, revealing metastable phases such as structural glasses and quenched alloys. Whether such thermally quenched metastability can be realized in metal-insulator transitions has remained an open question because these transformations are governed by collective electronic reorganization rather than atomic diffusion. We demonstrate that rapid cooling exceeding 10$^9$ K s$^{-1}$ kinetically avoids the metal-insulator transition, stabilizing a long-lived metastable metallic phase in tungsten-substituted VO$_2$. Temperature-dependent relaxation reveals nucleation-dominated kinetics with a thermal activation barrier introduced by tungsten substitution. Our results establish elemental substitution as a route to thermally quenched metastability in metal-insulator transitions, expanding metastable phase control to electronic phases.
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All authors Hiroshi Oike, Yasunori Takahashi, Keisuke Shibuya, Masaki Nakano, Tatsuki Hanada, Motoaki Hirayama, Hiroko Tokoro, Fumitaka Kagawa

Strongly Correlated Electrons

Field-amplified readouts of weak altermagnetic exchange in MnF$_2$

Guowen Jiang, Feilong Wang, Yunhua Wang et al. (+4 more)

MnF$_2$, the textbook two-sublattice antiferromagnet, has reemerged as a prototypical altermagnet, yet the sublattice-odd exchange that defines this identity remains under active debate: it enters the magnon splitting only in quadrature with the dipole–dipole interaction, its magnitude suppressed and its sign erased. An overdetermined first-principles total-energy mapping resolves this scale as a seventh-neighbor imbalance $\delta{J_7}\simeq+8~\mu$eV. The resulting Hamiltonian, with the dipole–dipole interaction included explicitly, reproduces the low-energy gap and the visible finite-momentum splitting. A longitudinal field $B\parallel c$ then acts as a linear amplifier of the hidden scale, opening two signed, field-linear readouts. The first is the compensation field $B^\ast(\mathbf Q)$, the position of minimum splitting, which is equal and opposite at the rotation-related partner momenta: a shift from zero field is itself evidence of a finite imbalance, its side gives the sign, and its magnitude, $|B^\ast|\simeq0.34$~T here, gives the scale. The second is the fixed-field contrast of the partner splittings, $\simeq0.14$~meV at $1$~T, six times the zero-field excess: a sign check from just two spectra. Both readouts survive a $0.12$~meV energy resolution, and the construction carries over to any easy-axis collinear altermagnet, bringing $\mu$eV altermagnetic exchange within present instrumental reach.
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All authors Guowen Jiang, Feilong Wang, Yunhua Wang, Fawei Zheng, Bin Xi, Hong-Gang Luo, Jize Zhao

Strongly Correlated Electrons

Competition between Geometrical Frustration and the Kondo Effect in CePdAl Revealed by High-Resolution Magnetization

Yusei Shimizu, Shota Nakamura, Yoichi Ikeda et al. (+4 more)

CePdAl is a heavy-fermion compound with a quasi-kagome structure, where geometrical frustration competes with the Kondo effect. Using a high-sensitivity magnetometer, we observe clear first-order metamagnetic transitions without magnetization plateaus in CePdAl at 80 mK, indicating a lifting of frustration through the suppression of the Kondo effect and spin flips of ordered moments under fields. An anomaly in the nonlinear magnetic susceptibility at 4.3 T suggests nondipolar correlations in the polarized paramagnetic state. Furthermore, we found no evidence of non-Fermi-liquid behavior in the high-field region, where the antiferromagnetic order is completely suppressed. These findings establish the essential thermodynamic constraints for understanding the field-induced spin-liquid state in CePdAl.
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All authors Yusei Shimizu, Shota Nakamura, Yoichi Ikeda, Yohei Kono, Shunichiro Kittaka, Toshiro Sakakibara, Yosikazu Isikawa

Wednesday 26 August

Strongly Correlated Electrons · Cross-listed from math-ph

Quantum cellular automata and invertible phases of matter

Corey Jones, Nikita Sopenko and Ryan Thorngren

We introduce and study (fermionic and bosonic) invertible quasi-local algebras over uniformly locally finite metric spaces $X$ with infinite-dimensional local von Neumann algebras. We show that the group of Brauer equivalence classes of such algebras is isomorphic to both the group of phases of invertible states and the group of stable equivalence classes of quantum cellular automata over $X\times \mathbb{Z}$. Using K-theory of the symmetric monoidal category of invertible quasi-local algebras and bounded spread isomorphisms, we propose a definition of an $\Omega$-spectrum of invertible phases as conjectured by Kitaev. We then show that the $c=\frac{1}{2}$ chiral Majorana fermion net and the $(E_{8})_{1}$ conformal net provide Brauer non-trivial invertible quasi-local algebras, thus providing explicit constructions of non-trivial invertible states and quantum cellular automata on $\mathbb{Z}^{2}$. In addition, we show that the time-slice nets of rational diagonal conformal field theories admit lattice degrees of freedom, which implies the discretization of any holomorphic conformal net is invertible.
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Strongly Correlated Electrons

Dynamical signatures of deconfined spinons in dimerized sawtooth chains

Nishan Ranabhat, Brandon B. Le, Seung-Hun Lee et al. (+1 more)

We study the ground-state properties and dynamical response of the Heisenberg model on the sawtooth chain in and away from the exactly solvable valence-bond-solid (VBS) point. We employ U(1)-symmetric density-matrix renormalization group (DMRG) and time-dependent variational principle (TDVP) methods to compute equilibrium diagnostics and the zero-temperature dynamical structure factor (DSF) $S^{zz}(q,\omega)$ across the dimerized phase, a valence-bond-ordered state in which the two symmetry-equivalent apex–base bonds of each triangle develop unequal spin correlations, probing the approach to the continuous lower phase boundary, the exact VBS point, and the approach to the first-order upper boundary. In every regime, the DSF is a broad continuum dominated by a bright band at its lower edge, with the intensity at the one-triplon energy $\omega \simeq J_{AB}$ suppressed. We identify the spectrum as a deconfined two-spinon continuum of kink and antikink domain walls between the two degenerate singlet coverings. Closed-form spinon dispersions fix the continuum edges and track the dominant band across the zone in all three regimes, while an explicit finite-separation two-kink calculation in a constrained Hilbert space reproduces the measured intensity distribution. Our results provide a microscopic picture of fractionalized excitations in the dimerized sawtooth chain and are relevant to the recently discovered Ti$^{3+}$ kagome fluorides, where strongly anisotropic exchange interactions can generate sawtooth-chain building blocks.
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All authors Nishan Ranabhat, Brandon B. Le, Seung-Hun Lee, Gia-Wei Chern

Strongly Correlated Electrons

Time and Momentum Resolved Tunneling Spectroscopy of Floquet dynamics

Lucas Q. Silveira and Adrian E. Feiguin

Periodically driven quantum systems provide a powerful route to engineer novel states of matter by controlling their effective Hamiltonians through external fields. However, most treatments are usually simplified by considering the high-frequency limit, and do not account for the processes taking place in the transient regime during the onset of the drive. In this work, we introduce a time and momentum resolved tunneling spectroscopy protocol to probe the instantaneous energy spectrum of Floquet-driven systems beyond the high-frequency regime, capturing both emergent effects and non-adiabatic phenomena without requiring explicit reconstruction of the full time-dependent Green's function. We benchmark the method on driven non-interacting fermionic models, and then generalize the approach to strongly correlated systems with the aid of time-dependent density matrix renormalization group techniques. We also provide a microscopic description to the emergence of in-gap states under resonant driving, and briefly explore its finite temperature analog.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Lieb-Schultz-Mattis Constraints for Quantum Channels: A Spacetime-Duality View

Sarang Gopalakrishnan, Yu-Jie Liu, Tsung-Cheng Lu et al. (+2 more)

Quantum anomalies strongly constrain the possible behavior of many-body systems. A prime example is the Lieb-Schultz-Mattis (LSM) theorem, which relates UV symmetry and filling constraints to IR features of the energy spectrum and ground-state structure. Here, we ask how LSM constraints shape dynamical signatures and temporal correlations in open quantum systems. Using a spacetime duality, we show that the Liouvillian of a $d$-dimensional repeated quantum channel with a mixed anomaly between strong $S$ and weak $G$ symmetry can be mapped to a $(d{+}1)$-dimensional mixed-state symmetry-protected topological (mSPT) phase. Under this correspondence, the initial and steady states of the channel are identified with boundary states of the higher-dimensional mSPT in the presence of bulk projection. We further introduce the twisted Renyi-$N$ correlator (TRNC) as a probe of temporal correlations in the channel and demonstrate that it is dual to the mSPT strange correlator, providing a direct bulk-boundary route to diagnose long-range temporal order implied by the LSM anomaly. Finally, we identify the Liouvillian singular spectrum, rather than the Liouvillian spectrum itself, as a more fundamental diagnostic of quantum anomalies, and show that it is dual to the operator entanglement spectrum of the mSPT.
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All authors Sarang Gopalakrishnan, Yu-Jie Liu, Tsung-Cheng Lu, Frank Pollmann, Yizhi You

Strongly Correlated Electrons

Statistics as a local phase: crystalline order and quench dynamics of emergent dimers in Ising gauge theories

Umberto Borla, Riccardo Cioli and Jad C. Halimeh

How does the Bose or Fermi statistics of microscopic particles survive when confinement binds them into emergent bosonic composites? We address this question in the strong-coupling limit of a $2+1$D $\mathbb{Z}_2$ lattice gauge theory, where charges are confined into tightly bound pairs that can be described by an effective dimer model. We find that the statistics of the underlying matter is encoded entirely in a single local hopping phase $\varphi$ -$0$ for bosons, $\pi$ for fermions. Treating $\varphi$ as a continuous parameter that interpolates between the two, we map the ground-state phase diagram with the help of tensor-network methods. The angle $\varphi$ itself drives a transition between a dimer-superfluid and a dimer-charge density wave state, while the magnetic coupling binds neighboring dimers into resonating pairs, in competition with the inter-dimer repulsion. We identify a novel gapped phase in which dimer pairs crystallize into an ordered pattern of resonating plaquettes. Finally, we propose a quench protocol under which identical dimer configurations evolve in markedly different ways depending on the statistics of their constituents. This provides a dynamical probe of the internal structure of dimers, and allows to detect ordered phases through real-time signatures, within reach of simulators that natively realize bosonic degrees of freedom.
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Strongly Correlated Electrons · Cross-listed from hep-th

Why Cooper pairs live in AdS2: a spectral analysis of the Yukawa-SYK model

Veronika Carolin Stangier and Jörg Schmalian

We establish the spectral foundation of the geometric formulation of Cooper pairing in the Yukawa–Sachdev–Ye–Kitaev model. Starting from the large-$N$ bilocal effective action, we derive the Gaussian fluctuation kernel in the even-frequency spin-singlet Cooper channel. Following the construction of Maldacena and Stanford, we determine the kernel eigenvalue $k\left(h\right)$ analytically for arbitrary conformal weight $h$ and resolve the pairing fluctuations into the continuous and discrete sectors of the associated de-Sitter space Laplacian. We show that the superconducting instability and the universal low-energy fluctuations near it reside entirely in the continuous scattering sector, while the discrete modes remain non-critical. Expanding the kernel about the lowest continuum mode yields a Klein–Gordon action on ${\rm dS}_2$, restricted to the continuous spectral subspace. This is precisely the subspace on which the inverse Radon transform to ${\rm AdS}_2$ is well defined. The projected bilocal Cooper-pair field can therefore be mapped onto a scalar matter field propagating in ${\rm AdS}_2$, without requiring any further spectral restriction on the bulk theory. Our results provide the missing microscopic justification for the projection implicit in earlier holographic formulations and clarify how a local bulk field emerges from the bilocal pairing theory.
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Strongly Correlated Electrons · Cross-listed from cond-mat.supr-con

Exact pair density wave in topological moire flat bands and universal superfluid stiffness

Zhengzhi Wu, Ming-rui Li and Hong Yao

Pair-density waves (PDWs) are unconventional superconducting states beyond the BCS paradigm, but identifying them unambiguously in microscopic lattice models is generally challenging due to various competing orders. In particular, an exact realization of PDW in interacting models with topological bands remains elusive. Here we construct an interacting model on a twisted bilayer checkerboard lattice (TBCB) featuring topological flat bands, and rigorously show that an exact PDW ground state can be induced by quantum geometric nesting (QGN), owing to its momentum-space nonsymmorphic symmetry. We further prove that the superfluid stiffness of any nondegenerate QGN superconductor (including the PDW studied here and uniform superconductor) obeys the universal relation $D_s=2N_{\rm flat}\nu(1-\nu)m_{\rm pair}^{-1}$, where $N_{\rm flat}$, $\nu$, and $m_{\rm pair}$ are the number of flat bands, flat band filling, and the two-particle effective mass, respectively. Our results reveal a rich interplay among PDW order, quantum geometry, and band topology.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

Multicomponent Magnetic Domain Walls in Rhombohedral Graphene

Mainak Das, Nemin Wei and Chunli Huang

Spatial textures of magnetic order, such as domain walls and skyrmions, are fundamental objects in magnetism. In rhombohedral multilayer graphene, magnetic order involves spin and valley degrees of freedom, opening the possibility of qualitatively new spatial textures. Here, we explore this possibility through a microscopic study of a one-dimensional domain wall in the valley-imbalanced quarter-metal phase of rhombohedral graphene. We uncover two different classes of domain walls. One resembles a conventional magnetic domain wall, locally rotating between the two bulk states, whereas the other is intrinsically multicomponent and explores states that are not occupied in either bulk domain. Which texture is realized is controlled by the competition between intervalley Hund's coupling and spin-orbit coupling, and we identify experimental signatures to distinguish them. For a superconducting junction formed across the wall, we further show that the superconducting phase difference couples directly to the intervalley-coherent phase of the texture, allowing precession of this internal phase to generate a voltage. This mechanism provides an explanation for the resistive domain walls recently observed in chiral superconductors [arXiv2605.13303] and predicts accompanying magnetization oscillations that could be detected using GHz-frequency AC probes. Our theory establish a microscopic connection between multicomponent magnetic textures, their internal dynamics, and superconducting transport.
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Strongly Correlated Electrons

Parity Anomaly as Modular Commutator with Massless Dirac Fermion

Meng Zeng

The modular commutator $J(A,B,C) = i\langle[K_{AB},K_{BC}]\rangle$ extracts the chiral central charge $c_-$ from a single bulk wavefunction of a gapped 2d state, where $3J/\pi=c_-$. Inspired by the recent developments in the field of gapless symmetry-protected topological phases, we ask: what does the modular commutator measure, if it is well-defined at all, when the 2d bulk becomes gapless? Several interesting new insights can already be obtained using the simple Haldane honeycomb model. For the critical point hosting an isolated Dirac node we find that $J$ remains sharp: it converges to a half-quantized value, with corrections that decay as a power law in the subsystem size rather than exponentially, mirroring the power-law correlations in gapless systems. We prove the half-quantization using an emergent reflection symmetry of the massless Dirac cone, and show that the half-quantized contribution comes from the other gapped cone (the massive partner of the massless one). This massive partner can be interpreted as the physical incarnation of the Pauli-Villars regulator, which is the origin of the parity-breaking level-$\frac{1}{2}$ Chern-Simons term (with half-quantized Hall conductance) and the parity anomaly. When protected chiral edge modes coexist with a bulk Dirac node we obtain $3J/\pi = c_-+\frac{1}{2}$. The half-quantization is also shown to be robust against tripartition deformation, tuning Dirac velocity and Dirac cone anisotropy. We further investigate other types of gaplessness—quadratic nodes (in contrast to linear Dirac) and the case with Fermi surface—and show that the robust half-quantization of $J$ is lost in such non-Dirac cases. These results generalize the modular commutator beyond gapped phases, and at the same time provide an information-theoretic measurement of the parity anomaly.
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Strongly Correlated Electrons

Incommensurate spin fluctuations in one-dimensional Kondo metal CeCo2Ga8

Yixuan Huang, P. Murgatroyd, Yi Wu et al. (+15 more)

We present an experimental and numerical study of the spin fluctuations in 1D Kondo metal CeCo$_2$Ga$_8$. Using inelastic neutron spectroscopy, we measure highly one-dimensional magnetism with low-energy incommensurate short-ranged magnetic fluctuations. ARPES similarly shows a highly one-dimensional electronic band structure, confirming the one-dimensional nature of the system. We use density matrix renormalization group (DMRG) simulations of the 1D Kondo lattice model to interpret the measured spectrum, which successfully reproduce the neutron scattering features. We are thus able to place CeCo$_2$Ga$_8$ within the emergent incommensurate phase of the 1D Kondo lattice phase diagram, and demonstrate that the Kondo lattice simulated non-perturbatively is an accurate microscopic model for heavy fermion physics. This shows CeCo$_2$Ga$_8$ to be one-dimensional despite its complexities, and reveals a coexistence of low-energy Kondo and magnetic features in its inelastic spectrum.
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All authors Yixuan Huang, P. Murgatroyd, Yi Wu, M. Cook, P. F. S. Rosa, E. D. Bauer, Asish K. Kundu, A. Rajapitamahuni, E. Vescovo, S. Zhang, V. Anil, P. Piyawongwatthana, N. Murai, M. Kofu, K. M. Shen, F. Ronning, Jian-Xin Zhu, A. Scheie

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

Electrical manipulation of oxygen stoichiometry in multiterminal YBa$_2$Cu$_3$O$_{7-\delta}$ junctions

Daniel Stoffels, Caio C. Quaglio-Gomes, Nicolas Lejeune et al. (+7 more)

Local manipulation of oxygen stoichiometry offers a route to control the electronic properties of complex oxides, yet the selective modification of individual current-carrying branches through oxygen redistribution remains unexplored in multiterminal high-temperature superconducting junctions. In a YBa$_2$Cu$_3$O$_{7-\delta}$ Y-shaped three-terminal device, we demonstrate the possibility to electrically control oxygen vacancy migration on a hand-picked terminal while largely preserving the other two. Oxygen-depleted propagating fronts are directly visualized by the resulting change in optical reflectivity and they are linked to the evolution of the electrical response. The process is highly directional and determined by the polarity of the applied current, allowing for the creation of either a converging or a diverging propagating front from the central node of the Y-shaped device. The associated changes in resistance exhibit relaxation on a timescale of minutes, driven by the vacancy concentration gradient. Effects of oxygen migration are also mapped by Kelvin Probe Force Microscopy and Scanning Laser Microscopy, which probe work-function changes and spatially resolved variations in the superconducting transition, respectively. Notably, the Tc contrast revealed by the latter provides a quantitative handle on the underlying oxygen content, enabling direct visualization of oxygen redistribution. Finite-element modeling and nanoprobe X-ray diffraction qualitatively reproduce the observed vacancy redistribution. These results establish a post-fabrication route to locally tune properties of superconducting multiterminal devices such as nanocryotrons, yTron, and tunable weak links.
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All authors Daniel Stoffels, Caio C. Quaglio-Gomes, Nicolas Lejeune, Emile Fourneau, Pedro Schio, Huidong Li, Lourdes Fabrega, Anna Palau, Maycon Motta, Alejandro V. Silhanek

Strongly Correlated Electrons

Rare-earth oxysulfides RE$_2$O$_2$S as model mixed-anion frustrated magnets

Austin M. Ferrenti, Ksenia Khoroshun, Mohamed Oudah et al. (+3 more)

The study of low-dimensional and anisotropic magnetism is a promising avenue for the discovery of novel quantum phenomena. Mixed-anion materials, defined by the coordination of metal cations by two or more distinct anionic species, provide an intrinsically anisotropic platform for the tuning of structural, magnetic, and electronic properties. In this work, we report the synthesis and characterization of a family of rare-earth oxysulfide (RE$_2$O$_2$S) antiferromagnets (AFM) possessing a triangular-bilayer slab lattice geometry. Long-range AFM order is observed for the majority of compositions, with several (RE = Ce, Pr, Nd, Sm) having been previously unreported. Although assumed to form stoichiometrically, pair distribution function (PDF) analysis provides evidence for significant, synthesis-dependent interslab structural disorder as RE$_2$O$_{2+x}$S$_{1-x}$, resulting in significant variability in the bulk magnetic response of the Nd member. This work highlights the tunability of frustrated magnetic ground states in rare-earth-based mixed-anion materials, and the importance of thorough structural characterization in the discovery of new mixed-anion magnets.
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All authors Austin M. Ferrenti, Ksenia Khoroshun, Mohamed Oudah, Graham King, Jonathan Gaudet, Alannah M. Hallas

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

Symmetry Origins of the Field-Free Superconducting Diode Effect in the Kagome Superconductor CsV$_3$Sb$_5$

Xin-Jie Liu, Shengbiao Sun, Ke-Fan Song et al. (+14 more)

Field-free superconducting diode effects require both inversion-symmetry breaking and an internal time-reversal-symmetry (TRS) breaking field, making them sensitive probes of hidden order in superconductors. In centrosymmetric kagome AV$_3$Sb$_5$, the inversion symmetry generally should generally preclude the observation of the superconducting diode effect. Furthermore, though TRS breaking has been reported in the superconducting regime of CsV$_3$Sb$_5$, whether it is generated by superconductivity or inherited from charge-density-wave (CDW) order remains unresolved. Here we show that pristine CsV$_3$Sb$_5$ devices exhibit no intrinsic field-free superconducting diode effect, whereas surface oxidation or asymmetric etching activates a large nonreciprocal supercurrent. Moreover, the response is stochastic, with sweep-dependent polarity and magnitude, indicating metastable TRS-breaking domain configurations. Small out-of-plane magnetic fields stabilize the superconducting diode response, consistent with field selection of such domains. Finally, when long-range CDW order is suppressed by Ti doping, the SDE disappears. Our results establish the symmetry requirements for the field-free SDE in CsV$_3$Sb$_5$, reveal its stochastic domain-controlled character, and link superconducting-state TRS breaking to CDW-related order.
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All authors Xin-Jie Liu, Shengbiao Sun, Ke-Fan Song, Jia-Peng Peng, Xilin Feng, Lang Xiao, Tong Liu, Qilin Han, Ya-Qing Bie, Ning Kang, Xiaosong Wu, Yanfei Wu, Shouguo Wang, Kam Tuen Law, Shuo Wang, Dapeng Yu, Ben-Chuan Lin

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

Size and Impurity Effects on Scattering of Valley Hall Modes in Gate-Defined Bilayer Graphene Superlattices

Marcus N. Kanestrøm, Antonio L. R. Manesco and D. O. Oriekhov

In the present paper we perform a tight-binding simulation of gate-defined islands in Bernal bilayer graphene (BLG). The inversion of the gap sign on the boundaries of the islands creates topologically-protected valley Hall modes. We focus on the specific questions of whether the valley Hall modes around such islands could serve as a host for quantum walks or simulate weakly coupled systems, and how their tunneling is affected by in-gap impurities. In addition, we discuss the effect of misalignment of top and bottom gate patterns on the tunneling properties between islands. Our main results show that resonant tunneling via an impurity enhances overlap between superlattice islands, while misalignment does not break topological protection over a wide parameter regime. In addition, we study the two-island geometry and show that it is possible to leverage suppressed scattering to place islands more densely on a single sample.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Magic of Kitaev spin liquids

Eleonora Lamma, Tim Bauer, Marcello Dalmonte et al. (+1 more)

Quantum spin liquids (QSLs) are long-range entangled phases of matter and a natural setting for exploring how quantum correlations generate quantum complexity. Motivated by the emergence of magic, or nonstabilizerness, as a diagnostic of many-body complexity beyond entanglement, we study magic of QSLs by computing the stabilizer Rényi entropy (SRE) of the Kitaev honeycomb model. We derive a correspondence between Pauli strings and products of itinerant Majorana operators in the model's free-fermion description; this enables the sampling of SRE using an optimized algorithm for Gaussian states in systems with thousands of spins. Our results show that magic is largest in the gapless phase, where subleading volume-law corrections indicate nonlocal contributions, while in the gapped phases, SRE decreases in quantitative agreement with a perturbative expansion that we develop in the anisotropic limit. At the topological phase transition, SRE exhibits universal scaling dictated by critical exponents.
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All authors Eleonora Lamma, Tim Bauer, Marcello Dalmonte, Mario Collura

Strongly Correlated Electrons

Fate of the non-Abelian Moore-Read manifold under the non-Hermitian skin effect

Jiaxuan Guo, Simin Nie, Xiting Zhang et al. (+1 more)

We study a non-Abelian Moore-Read fractional Chern insulator under a translation-preserving, nonreciprocal deformation that generates the non-Hermitian skin effect under open boundaries. The model combines the imaginary-gauge Hatano-Nelson deformation with a kagome-lattice three-body interaction designed to stabilize Moore-Read order at $\nu=1/2$. Our primary diagnostic is the biorthogonal $(2,4)$-admissible particle-entanglement counting of the sixfold Moore-Read manifold, the standard Moore-Read fingerprint. Across three sizes ($N=16,20,24$), the counting locks to the clean references 1308, 3965, and 9282 over finite nonreciprocity windows through $\gamma\le0.55$, $0.65$, and $0.74$, respectively, with positive reference-rank entanglement gaps. Within every reported window the count is unchanged by the spectral readings tested; at $N=16$ it is also unchanged across three reduced density operators, with all 15 combinations returning 1308. The sixfold pattern for even $N_f$ and the adiabatically tracked Ising-odd doublet remain separated over the tested range $\gamma\le0.6$. Beyond a geometry-dependent threshold the instantaneous-lowest-six reference-rank gap drops sharply and its counting destabilizes. At $N=24$ a sector-0 branch pair becomes complex conjugate over a narrow interval inside the delocking bracket; both continuations through the interval are delocked at the tested PES points $\gamma=0.76$, $0.77$, and $0.80$. A same-lattice Abelian $\nu=1/3$ Laughlin realization retains its counting to $\gamma=1.0$, so its counting is the more robust. On the torus the eigenstates remain extended; under open boundaries the right and left states skin-localize at opposite edges while the biorthogonal particle-entanglement spectrum is invariant under the imaginary-gauge similarity, so the torus and the open cylinder probe the same deformation under periodic and open boundaries.
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All authors Jiaxuan Guo, Simin Nie, Xiting Zhang, Fritz B. Prinz

Strongly Correlated Electrons

Quasi two dimensional magnetic structure of the triclinic double perovskite Ca$_2$CuWO$_6$

Bangye Qin, Dmitry D. Khalyavin, Xuan Liang et al. (+3 more)

We present the antiferromagnetic ground state of the triclinic double perovskite Ca$_2$CuWO$_6$solved by neutron powder diffraction, and analyze it in direct comparison with tetragonal Sr$_2$CuWO$_6$. Below $T_\mathrm{N} \simeq 32$ K, the magnetic Bragg reflections of Ca$_2$CuWO$_6$ are indexed by the commensurate propagation vector $\mathbf{k}=(\tfrac{1}{2},\tfrac{1}{2},0)$ in its native $P\bar{1}$ cell. Rietveld refinement yields a collinear structure with equal-magnitude, antiparallel moments on the crystallographically inequivalent Cu1 and Cu2 sites and an ordered moment of $0.66(3)~\mu_{\mathrm B}$ per Cu at 1.5 K. A direct comparison with Sr$_2$CuWO$_6$ is obscured by different crystallographic settings and orientations of the cooperative Jahn-Teller elongation axes. Hence, we introduce a common crystallographic supercell through which effects of symmetry lowering from tetragonal to triclinic in the double perovskite are explored: Apparently different magnetic propagation vectors map onto the same supercell wave vector, revealing a common magnetic structure stabilized by tungsten-mediated, second-neighbor interactions. Mean field calculations further show that tetragonal symmetry preserves the degeneracy of four magnetic $\mathbf{k}$-domains in Sr$_2$CuWO$_6$, whereas the triclinic splitting of symmetry-related exchange pathways in Ca$_2$CuWO$_6$, most strongly within the Cu2 network, selects a single $\mathbf{k}$-domain. These results establish the magnetic ground state of Ca$_2$CuWO$_6$ and show how symmetry breaking selects a given ordered state without changing the underlying magnetic motif of the Sr analogue.
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All authors Bangye Qin, Dmitry D. Khalyavin, Xuan Liang, Kazunari Yamaura, Alexei A. Belik, Roger D. Johnson

Strongly Correlated Electrons

Phase calibration of quantum oscillations in the magnetostrictive coefficient using the topological antiferromagnet YbMnBi$_2$

Qin Deng, Long Zhang, Zeyu Li et al. (+6 more)

The Berry phase accumulated along a cyclotron orbit encodes important information about electronic band topology and is commonly inferred from the phase of quantum oscillations. Measurements of the ac magnetostrictive coefficient have recently emerged as a sensitive thermodynamic probe of quantum oscillations, but the phase offset has not been experimentally calibrated. Here, using the topological antiferromagnet YbMnBi$_2$, we calibrate this offset by directly comparing quantum oscillations in magnetization with those in the ac magnetostrictive coefficient. Measurements of both responses on the same single crystal reveal a single fundamental frequency of approximately 160 T in fields up to 14 T, enabling a direct phase comparison free from ambiguities associated with multiple frequencies. We observe an approximately $\pi/2$ relative phase shift between the two oscillatory responses, consistent with the Maxwell relation linking the magnetostrictive coefficient to the stress derivative of magnetization. Our results establish the appropriate phase needed to extract cyclotron-orbit phase information from quantum oscillations in the ac magnetostrictive coefficient.
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All authors Qin Deng, Long Zhang, Zeyu Li, Ying Zhu, Shuai Wu, Yan Liu, Aifeng Wang, Yu Pan, Yisheng Chai

Strongly Correlated Electrons

Electric excitation of spin resonance in altermagnetic and antiferromagnetic conductors

R. Ramazashvili, V. Shablenko and Ya. B. Bazaliy

We predict electric-dipole spin resonance (EDSR) in altermagnetic conductors: in a magnetic field ${\mathbf H}_\perp$, perpendicular to the magnetization axis, an AC electric field will induce a spin resonance peak above the lower threshold frequency $\omega_- = 2H_\perp$. In sufficiently clean samples, this peak shall be clearly visible on the background of ohmic absorption. EDSR can thus serve as a diagnostic of altermagnetism in conducting materials and as a means to distinguish it from higher-symmetry antiferromagnetic order.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

Signatures of a ferro-Josephson effect in twisted graphene

Ruiheng Su, Zhenxiang Gao, Christopher Coleman et al. (+9 more)

When a spin-polarized current is driven across a magnetic domain wall, the resulting spin-transfer torque may, beyond a critical threshold, set the wall's moments into precession. This precession modulates the Berry curvature experienced by electrons traversing the wall, producing an electromotive force that is topological in nature and proportional to the precession frequency, mapping precisely onto the DC Josephson effect and leading to the name ferro-Josephson effect. We report signatures consistent with this effect in a twisted graphene van der Waals heterostructure, where spin and valley textures are linked by exchange, Hund's coupling, and spin-orbit interactions. Tuned to fillings where the isospin degeneracy is spontaneously broken, the samples develop a sharp peak in the longitudinal resistance within a fraction of a millitesla of $B_\parallel=0$—a peak that disappears as the current is reduced toward zero. In differential resistance the feature resolves into sharp resonances that disperse with $B_\parallel$ on microtesla and picoampere scales. We argue that these arise from the current-driven precession of spin-domain-wall moments, in competition with the in-plane anisotropy set by a minuscule applied field, and that they establish nonlinear transport as a sensitive probe of isospin domain-wall dynamics at energy scales far below $k_BT$.
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All authors Ruiheng Su, Zhenxiang Gao, Christopher Coleman, Manabendra Kuiri, Dacen Waters, Kenji Watanabe, Takashi Taniguchi, Matthew Yankowitz, Nemin Wei, Chunli Huang, Allan H. MacDonald, Joshua Folk

Tuesday 25 August

Strongly Correlated Electrons

Dynamical splitting and a nodal Bose liquid in 2d chiral XYZ model

Tarun Grover

We study a class of Hamiltonians with a structure that we call "dynamical splitting": the Hamiltonian terms can be divided into two sets acting on the same degrees of freedom such that every term in one set commutes with every term in the other, although terms within either set do not all commute. This structure yields an algebraic duality to effective degrees of freedom on which the two parts of the Hamiltonian act disjointly, enabling exact diagonalization on lattices with approximately twice as many spins as usually accessible. We exploit it in the "chiral XYZ model", a geometrically frustrated spin-$1/2$ model on the triangular lattice which was previously introduced as a special limit of a Majorana-Hubbard model. This model also possesses anticommuting noncontractible line symmetries, which enforce an exact, topology-dependent degeneracy between locally indistinguishable states. We first study a $\mathbb{Z}_N$ clock generalization and find, at large $N$, a gapless ground state with three subsystem-symmetry-protected nodal lines. Exploiting dynamical splitting and the subsystem symmetries, we carry out exact diagonalization of the $N=2$ model on lattices up to $9\times9$ spins. The many-body gap and bipartite entanglement provide strong evidence for a gapless state consistent with the large-$N$ nodal structure: the entanglement scales as $L\log L$ and exhibits $1+1$-dimensional CFT-like chord scaling on cylinders. Finally, we study instabilities and proximate phases. In particular, we find evidence that a subsystem-symmetry-preserving deformation drives a finite coupling transition to a gapped phase with $\mathbb Z_2 \times \mathbb Z_2$ topological order.
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