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Physics Condensed Matter Strongly Correlated Electrons

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Saturday 29 August

Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Light-induced nonconservative static forces in many-body systems

Jinze Li, Xuemei Yang and Zhiyuan Sun

In a quantum many-body system, a periodic drive can often generate effective static forces on the slow collective degrees of freedom. We study the static forces generated by light on electronic order parameters in solid-state systems. We show that the forces can have nonconservative components that originate from dissipation, i.e., optical absorption. This effect is demonstrated in two nontrivial examples. In excitonic insulators, via interband excitations, the light field generates a nonconservative force on the phase of the excitonic order parameter. This force leads to an acceleration of the phase, which manifests as a shift of the photon emission peak from an exciton condensate. In materials with an incommensurate charge density wave, a propagating light field generates a nonconservative force on the phase of its order parameter. It drives the charge density wave into sliding motion, leading to a DC electric current via topological Thouless pumping.
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Strongly Correlated Electrons

Electronic phase separation and emergence of a nondimerized insulating phase in VO$_2$ $(110)_{\mathit{R}}$ ultrathin films

S. Inoue, D. Shiga, R. Hayasaka et al. (+3 more)

Using in situ photoemission spectroscopy and x-ray absorption spectroscopy, we investigated the thickness dependence of the electronic structure and V-V dimerization in VO$_2$/TiO$_2$ (110) ultrathin films, in which the one-dimensional V-V chains along the $c_{\mathit{R}}$ axis lie in the film plane. In VO$_2$ $(110)_{\mathit{R}}$ films, the reduction in dimensionality along the surface-normal direction is not expected to impose a geometric constraint on V-V dimerization, unlike in VO$_2$ $(001)_{\mathit{R}}$ films. Nevertheless, the characteristic spectral changes associated with the temperature-driven metal-insulator transition observed in thick films persist down to 1.5 nm, whereas at 1 nm an insulating electronic phase is observed without V-V dimerization. This behavior is highly similar to that reported for VO$_2$ $(001)_{\mathit{R}}$, suggesting that the enhancement of Mott instability resulting from reduced dimensionality is a common and essential driving force for the emergence of the nondimerized insulating phase in VO$_2$ ultrathin films. Meanwhile, unlike in VO$_2$ $(001)_{\mathit{R}}$, the nondimerized insulating phase in VO$_2$ $(110)_{\mathit{R}}$ coexists with the phase exhibiting the temperature-driven metal-insulator transition. Its fraction increases exponentially with decreasing thickness and becomes dominant at 1 nm. The corresponding effective critical thickness is estimated to be 2.2 nm. These results imply that the geometric orientation of the V-V chains dictates the spatial evolution of electronic phase separation via strain-mediated phase competition.
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All authors S. Inoue, D. Shiga, R. Hayasaka, K. Ozawa, A. F. Santander-Syro, H. Kumigashira

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

Doping-driven evolution of pairing symmetry in pressurized La$_3$Ni$_2$O$_7$

Hai-Yang Zhang, Yu-Jie Bai and Fan-Jie Kong

We investigate the superconducting pairing symmetry and its doping evolution in pressurized La$_3$Ni$_2$O$_7$. For the undoped compound, the most favorable pairing state is found to be $s_{\pm}$-wave, characterized by sign reversal of the gap functions between the Fermi pockets. A detailed analysis of the pairing interactions reveals that this unconventional state originates from repulsive interactions mediated by the magnetic odd modes of the bilayer nickelate. Upon hole doping, the $\gamma$ Fermi pocket expands, which amplifies the intrapocket repulsions on this pocket. These repulsions, driven by the magnetic even modes, gradually dominates the pairing interactions and ultimately drive a transition in pairing symmetry from $s_{\pm}$-wave to $d_{xy}$-wave in the heavily hole-doped regime. In stark contrast, the $s_{\pm}$-wave pairing persists under electron doping, even deep into the heavily electron-doped regime where a Lifshitz transition occurs. This finding suggests that the $\gamma$ Fermi pocket is not essential for the emergence of superconductivity in bilayer nickelates. In fact, the $s_{\pm}$-wave pairing becomes more robust in the absence of the $\gamma$ pocket, as spin fluctuations are strongly enhanced by the favorable nesting between the $\alpha$ and $\beta$ pockets — a condition guaranteed by Luttinger's theorem and the Fermi surface topology. We believe that exploring the doping evolution of superconducting pairing will open a new realm for testing the pairing mechanism in pressurized La$_3$Ni$_2$O$_7$.
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Strongly Correlated Electrons

Real-space manifestation of ferroic multipoles in altermagnetic MnF$_2$

Iurii Kibalin, Dalila Bounoua, José A. Rodriguez Velamazán et al. (+9 more)

Altermagnets are unconventional spin split magnets arising from the zero spin-orbit coupled limit. They host a magnetic multipolar order parameter yet direct real-space observation of these multipoles has remained elusive. Here we use polarized-neutron diffraction to reconstruct the three-dimensional magnetization density of the prototypical altermagnet MnF$_2$. By exploiting symmetry-selective magnetic reflections, we separate the dominant spherical Mn$^{2+}$ contribution from the much weaker anisotropic Mn magnetization and the covalent spin polarization of the fluorine ligands. The reconstructed spin density reveals a finite fluorine ion moment together with an anisotropic Mn magnetization consistent with the symmetry-allowed altermagnetic rank-5 magnetic multipole $O_{52}$(magnetic triacontadipole). These results provide direct real-space evidence of ferroic multipolar order in an altermagnet and establish polarized-neutron diffraction as a powerful probe of hidden magnetic multipoles in quantum materials.
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All authors Iurii Kibalin, Dalila Bounoua, José A. Rodriguez Velamazán, Oscar Fabelo, Navid Qureshi, Quentin Faure, Philippe Bourges, Victor Balédent, Jian-Rui Soh, Jeffrey Rau, Paul McClarty, Arsen Gukasov

Strongly Correlated Electrons

Duality Between Twist-Angle Disorder and Non-Hermitian Disorder

Yi-Ming Wu and Nicole S. Ticea

We propose and study a model of moire heterobilayer systems where the twist angle remains uniform and well defined only within a finite range, but deforms randomly at larger distances. The local twist angle is then subject to a certain probability distribution that penalizes large fluctuations around its mean value. Within the framework of the replica trick, we show that disorder averaging produces a nontrivial correlation with alternating sign between replicas, maximized only close the boundary of each local domain and along certain directions. We show that for the low-energy moire bands, exactly the same correlation can be generated in a dual model where fermions are coupled to non-Hermitian disorder, which can evade Anderson localization dynamically. This duality provides a new perspective to investigate twist-angle disorder in moire systems, and unveils some of the essential differences between twist-angle disorder and conventional disorder.
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Strongly Correlated Electrons

Enhanced Diffusion from Twist-Angle Disorder

Nicole S Ticea and Yi-Ming Wu

We consider the effect of twist-angle disorder on the single-particle properties of twisted bilayer systems. These materials are a natural playground for studying how tiny, uncontrolled spatial variations may become unusually consequential; a local change in the twist geometry can give rise to spatially-correlated alterations of the parent Hamiltonian, which in turn affect the coarse-grained properties of the substrate such as transport and ordering tendencies. In analogy to electrodynamics, where the magnetic field is given by the curl of the vector potential, we model the twist angle as the curl of the relative displacement between the two bilayers. We find that geometric scattering constraints imposed here by the twist structure substantially suppress momentum relaxation relative to mean-rate-matched white noise. We quantify these effects and show that the problem can be mapped onto a non-linear sigma model (NLSM).
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Friday 28 August

Strongly Correlated Electrons · Cross-listed from quant-ph

Spin-spin effects from non-relativistic limit of Dirac-Pauli-Maxwell Lagrangian

Radmehr Fathi and Nima Khosravi

It is natural to expect that the electromagnetic spin-spin interaction has roots in a more fundamental theory: quantum electrodynamics in this case. To show this, we take the non-relativistic limit of the Dirac-Maxwell Lagrangian, using the Foldy-Wouthuysen transformation and derive the Breit interaction by an alternative approach. By adding the Pauli term (i.e., a higher-order interaction between spin and the electromagnetic field), we calculate the correction terms to electromagnetic spin-spin interactions in the non-relativistic limit. Finally, we study some of the physical effects of these terms regarding spin-spin interactions and spin-spin entanglements. Accordingly, we provide theoretical estimates that are not yet accessible with current experiments.
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Strongly Correlated Electrons

Phase stability, charge ordering, and charge-liquid formation in the Falicov-Kimball model on triangular and kagome lattices

Ammar Nejati and Marvin Lenk

We present a systematic investigation of the stability of the phase diagram of the spinless Falicov-Kimball model on two-dimensional non-bipartite lattices, the triangular and kagome lattices, using Markov-chain Monte Carlo simulations. Three filling or chemical potential conditions are examined: fixed chemical potentials ($\mu_f = \mu_c = U/2$), "generalized" half-filling ($\bar{n}_f = 1/3$, $\bar{n}_c = 2/3$), and conventional half-filling ($\bar{n}_f = \bar{n}_c = 1/2$). For each condition, the effects of a perturbatively small next-nearest-neighbor hopping are studied. On the triangular lattice, Anderson insulator, Mott insulator, and charge-density wave (CDW) phases are found in all cases, with the CDW driven by Coulomb-interaction-mediated nesting. Evidence for a charge-liquid regime is found in the region between the weakly correlated regime and the CDW, characterized by competing charge-ordering wavevectors and the absence of universal scaling behavior, whose extent shrinks progressively from the grand-canonical to the conventional half-filling condition. On the kagome lattice, the CDW phase is completely absent; instead, an insulating ground state, plausibly of the Mott type, is found, with signatures of a possible quantum phase transition at zero temperature. Our results establish the crucial role of lattice geometry and particle-hole symmetry breaking in shaping the phase diagram of correlated electron systems.
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Strongly Correlated Electrons · Cross-listed from cond-mat.supr-con

Direct Evidence of Unconventional Superconductivity in Doped Kagome system RV$_3$Sb$_5$

Avior Almoalem, Yuqing Xing, Iksu Jang et al. (+7 more)

The superconducting pairing symmetry of kagome metals remains a central unresolved question largely because phase-sensitive experiments capable of distinguishing between different possible order parameters have been difficult to implement. The spatial and energetic characteristics of impurity bound states measured by spectroscopic-imaging scanning tunneling microscopy encode information on the superconducting order parameter. Here, we use impurity-bound state spectroscopy to investigate optimally doped RbV$_3$Sb$_{5}$ where the charge-density wave instability is fully suppressed. We find that the superconducting state is fully gapped and exhibits two distinct energy scales, consistent with a multiband order parameter. Atomic-scale spectroscopy around nonmagnetic defects reveals pronounced particle-hole asymmetric bound states. Comparison with theoretical calculations demonstrates that these bound states are incompatible with conventional $s$-wave and sign-changing $s^{\pm}$ pairing. Our calculations also show that the data are fully consistent with a chiral order parameter. Our results establish impurity-bound-state spectroscopy as a powerful phase-sensitive probe of superconductivity in kagome materials and provide strong evidence that optimally doped RbV$_3$Sb$_{5}$ realizes a fully gapped chiral superconducting state.
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All authors Avior Almoalem, Yuqing Xing, Iksu Jang, Daniel J. Schultz, Grgur Palle, Andrea N. Capa Salinas, Stephen D. Wilson, Rafael M. Fernandes, Jörg Schmalian, Vidya Madhavan

Strongly Correlated Electrons

Floquet engineering of competing antiferromagnetism and $d$-wave superconductivity on the square lattice

Zhaoyu Han and Subir Sachdev

We propose a driven Lieb–Hubbard quantum simulator whose prethermal dynamics realize a square-lattice spin-1/2 fermion model with independently tunable repulsive on-site and attractive bond interactions. Periodically modulating the charge-transfer offset between the site ($d$) and bond ($p$) orbitals of the Lieb lattice brings a $p$-orbital doublon energetically close to a pair in the $d$ manifold while keeping all $p$-orbital singlons off resonance, thereby creating a synthetic “negative-$U$” center on a Lieb-lattice bond site. Two controlled eliminations then generate a compact bond attraction in the reduced $d$-only model on the square lattice, despite the microscopic repulsion in the $p$ orbital. The resulting interaction $J$ is tunable independently of the Hubbard repulsion $U_d$ on the $d$ orbitals, while interference between photon-assisted paths provides access to an intermediate-coupling regime in which $J$ and $U_d$ are both comparable to the effective hopping. At half filling, a mean-field calculation in this regime finds adjacent antiferromagnetic and $d$-wave superconducting phases, as well as narrow coexistence regions, suggesting close competition between these orders. We discuss the branch-preparation, prethermal, and higher-band conditions required to translate the formal construction into an optical-lattice protocol. More broadly, our work identifies a structural similarity between Floquet systems and electron-phonon problems that may guide the design of novel quantum-simulation protocols.
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Strongly Correlated Electrons

Determinant Quantum-Quantum Monte Carlo: Coherent Auxiliary-Field Sampling

Xuepeng Wang, Sagnik Banerjee and Debanjan Chowdhury

We introduce determinant quantum-quantum Monte Carlo (DQ$^2$MC), a quantum algorithm that lifts the auxiliary-field sampling and averaging at the operational core of determinant quantum Monte Carlo onto a quantum computer. A determinant oracle synthesizes the DQMC amplitudes directly from a block encoding of the single-particle action matrix via quantum singular value transformations, so that the exponentially many Hubbard-Stratonovich weights are never enumerated, precomputed, or stored. Since the fermions are free for fixed auxiliary fields, the construction operates entirely at the single-particle level, requiring $O(\log N_{\mathrm{st}})$ system qubits and no Jordan-Wigner or Bravyi-Kitaev encoding, where $N_{\mathrm{st}}$ is the space-time volume. A full-quantum protocol makes observables interference amplitudes, eliminating the Markov chain and its autocorrelation time altogether; a hybrid quantum-classical protocol retains a constant-size active block of qubits and replaces the Metropolis-Hastings acceptance step with an exact heat-bath draw, so that cluster updates of any size are rejection-free, and passes only classical information between updates, admitting parallel tempering and distributed execution across quantum processors. The circuit-depth scales more favorably with spatial volume than classical DQMC, at the price of a post-selection overhead determined exactly by the largest target probability — polynomial for smooth distributions, exponential for sharply peaked ones. Finally, the reweighting estimator underlying the fermion sign problem maps exactly onto a quantum weak value, placing the exponential cost of sign-problematic DQMC in precise correspondence with the post-selection overhead of weak-value extraction.
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Strongly Correlated Electrons · Cross-listed from cond-mat.dis-nn

Fractal Confinement and Magnetic Self-sabotage of Current Flow: Electrons Near the Metal-insulator Crossover in a 2D $\delta$-layer

Xinghai Zhang, Matthew S. Foster and Markus Mueller

We study low-$T$ transport and itinerant magnetism in 2D $\delta$-doped semiconductors. Large-scale Hartree-Fock calculations with random hoppings and repulsion $U_0$ reveal two transport regimes near a critical density. The conductivity $\sigma(T)$ initially increases as $T$ drops below $U_0 / 10$. However, at $T \sim U_0/100$, a tiny density of magnetic moments forms, driving an insulating downturn. Fractal wavefunctions locally amplify magnetic interactions, initially concentrating currents into branched filaments, but ultimately choking them off via dynamic SU(2) symmetry breaking.
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Strongly Correlated Electrons

Interaction corrections to topological density three-point functions in two-dimensional Fermi liquids: a coadjoint orbit perspective

Akshay Pal, Andrew Lucas and Umang Mehta

Density three-point correlations are known to probe the topology of the Fermi sea in two-dimensional noninteracting systems. Here, we study how these correlations are modified by interactions using the coadjoint-orbit effective field theory. A key advantage of the coadjoint-orbit formulation is that it provides a systematic way to incorporate generalized Landau interactions in terms of bosonized degrees of freedom, mapping fermionic loop contributions onto simpler tree-level diagrams. We show that, for a general isotropic dispersion $\epsilon(p)$, even at linear order in the generalized Landau interaction, $\mathcal{O}(\mathcal{F}^{(2,0)})$, there exists a contribution proportional to the band curvature $\epsilon''(p_F)$ that changes the nonanalytic structure of the free density three-point correlation function. This contribution introduces a distinct nonanalytic structure beyond that found in either the noninteracting case or an interacting Galilean-invariant system, showing that interaction effects can modify the topology-detecting density three-point correlation.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci

Layer-Controlled Intermolecular Coupling and Many-Body Effects in C$_{60}$ Films

Hai-Lan Luo, Weitang Li, Luca Moreschini et al. (+4 more)

Crystalline C$_{60}$ is a molecular solid whose electronic properties emerge from the interplay of intermolecular hopping, electron correlations, and electron-vibration coupling. Unlike moir$\rm\acute{e}$ van der Waals heterostructures, where interaction strength is commonly tuned by twist angle, molecular materials offer a complementary route in which layer number, molecular orientation, and substrate registry provide experimentally accessible control parameters. Here we present a systematic thickness-dependent angle-resolved photoemission study of C$_{60}$ films, spanning the monolayer to the bulk limit. The HOMO-derived band exhibits a non-monotonic evolution: the intermediate-thickness film shows larger bandwidth, reduced effective mass, and pronounced gap-like and sub-band features. The experimental trends, together with Holstein-model simulations, point to strengthened effective intermolecular electronic coupling and enhanced electron-phonon-induced spectral renormalization in the intermediate-thickness regime. These results identify a dimensional crossover in C$_{60}$ films and establish layer number as an effective knob for engineering electronic structure and many-body interactions in molecular thin films.
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All authors Hai-Lan Luo, Weitang Li, Luca Moreschini, Jonathan Denlinger, Zhigang Shuai, Claudia Ojeda-Aristizabal, Alessandra Lanzara

Strongly Correlated Electrons · Cross-listed from hep-th

Positivity constraints on the dynamics of cusped impurities in CFTs

Jeevan Chandra

The cusp anomalous dimension is the universal logarithmic contribution to the free energy of a line defect with a cusp, and provides a useful observable characterizing defect dynamics. We generalize this notion to cusped line defects in the presence of a planar conformal boundary or interface. The geometry is characterized by three angles, and the distance of the cusp from the boundary or interface which separates short-distance and long-distance regimes. The resulting free energy contains two large logarithmic terms: a short-distance contribution governed by the usual vacuum cusp anomalous dimension, and a new long-distance contribution sensitive to the boundary or interface. Using reflection positivity for transverse deformations of the defect rays, we derive several constraints on the coefficients of these logarithmic terms, which can be packaged into negative semi-definiteness of their angular Hessians. We also derive constraints on the continuation of these coefficients to Lorentzian kinematics. We compute these coefficients and verify the constraints explicitly in free scalar and Maxwell theories and in planar $\mathcal N=4$ super-Yang-Mills theory at weak coupling for various choices of boundary conditions. At strong coupling, we compute the logarithmic coefficients in the holographic D3-D5 defect CFT and find a Gross-Ooguri-like phase transition between competing string worldsheets driven by the geometry of the cusp relative to the interface. We also observe a close connection of the cusp free energy in this setup with holographic corner entanglement entropy.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

Evidence for Three-component Interlayer Coherent Exciton Condensation

Subi Du, Xiaohan Zhang, Hongxi Song et al. (+8 more)

Increasing the number of internal components in a quantum many-body system can host collective orders inaccessible to simpler settings. Quantum Hall bilayers provide a canonical realization of interlayer exciton condensation, yet extending such coherence across three independently addressable electronic fluids has remained elusive. Here we report evidence for three-component interlayer coherent exciton condensation in triple-layer graphene system. Using Rydberg excitons in an adjacent WSe2 monolayer as a layer-sensitive optical probe, we resolve interaction-induced incompressibility at zeroth-Landau-level crossings for all three pairwise layer combinations, establishing top-middle, middle-bottom and top-bottom exciton condensate channels within the same device. Independent control of displacement field and interlayer bias continuously tunes these pairwise states towards a regime where Landau levels from all three layers approach simultaneous degeneracy. At their convergence, incompressibility persists while the exciton energy and spectral weight evolve smoothly between the pairwise limits, suggesting coherent participation of all three layers in a single three-component state. More broadly, the ability to independently control layer potentials and engineer interlayer interactions establishes multilayer graphene as a programmable synthetic dimension for exploring higher-component quantum Hall order and simulating strongly correlated quantum matter.
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All authors Subi Du, Xiaohan Zhang, Hongxi Song, Siyu Fan, Yiduo Wang, Zhenyu Wang, Song Liu, Kenji Watanabe, Takashi Taniguchi, Jiangping Hu, Yang Xu

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

Interplay between crystal structure and magnetism in CeCrB$_4$

Mirosław Werwiński, Andrzej Szajek and Andrzej Kowalczyk

CeCrB$_4$ belongs to the family of MTB$_4$ ternary metal borides, some of whose magnetic phases have recently been identified as quantum spin dimers. Employing density functional theory within the GGA+$U$ framework, this work investigates the key ground-state properties of this system, including its ferromagnetic ground state, the mixed-valence nature of cerium, and the charge transfer from the cationic cerium–chromium layers to the anionic boron layers. In particular, we focus on elucidating the bonding mechanism within the structurally embedded Cr-Cr dimers. Specifically, we evaluate a previously proposed interpretation that the localized Cr $3d_{z^2}$ states are molecular-like bonding and antibonding states. The calculated dependence of the $3d_{z^2}$ electronic structure on the intra-dimer distance correlates with the level-splitting characteristics known for classical homonuclear diatomic molecules.
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Strongly Correlated Electrons

Field-tuned quasiparticles and electronic structure in heavy-fermion YbNi4P2

Will Broad, Owen Moulding, Takaki Muramatsu et al. (+7 more)

We study the Fermi surface topology and quasiparticle properties in the heavy fermion compound YbNi4P2 at high magnetic fields using quantum oscillation measurements. We observe a large decrease of the quasiparticle mass with increasing field and demonstrate good qualitative agreement with the single-ion Kondo model. At the putative Lifshitz transition at 17 T, we observe a sudden change of quantum oscillation frequencies suggesting an abrupt change of the electronic structure and/or quasiparticle characteristics. Our results demonstrate the ability to tune the electronic structure and provide input for theoretical models of YbNi4P2 and correlated electron systems in high magnetic fields.
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All authors Will Broad, Owen Moulding, Takaki Muramatsu, Manuel Brando, Alix McCollam, Femke Bangman, Gertrud Zwicknagl, Kristin Kliemt, Cornelius Krellner, Sven Friedemann

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

Charge transfer and competing symmetry breaking drive orbital reconstruction and emergent ferromagnetism in insulating oxide superlattices

Nandana Bhattacharya, Ranjan Kumar Patel, Siddharth Kumar et al. (+13 more)

Electron correlation, hopping, and ligand-to-metal charge transfer collectively lead to diverse electronic and magnetic phenomena in 3$d$ transition-metal oxides, where directional d orbitals make hopping highly sensitive to symmetry-dependent orbital overlap. Heterostructure engineering with atomically flat interfaces adds symmetry-breaking charge transfer as a further route to emergent behavior, yet whether interfacial mismatch between constituent oxides of a superlattice shapes ground states independent of epitaxial strain remains unresolved. Here we examine superlattices combining NdNiO$_3$ with Mott-insulating NdMnO$_3$. Varying layer thickness and combining transport with X-ray spectroscopy, we show that electron transfer from NdMnO$_3$ to NdNiO$_3$ drives a room-temperature insulating state with a distinct electronic structure, accompanied by a reversal in orbital symmetry beyond simple strain considerations, underscoring the interface's central role. These reconstructions stabilize an emergent ferromagnetic insulating state arising from interfacial Ni$^{2+}$-O-Mn$^{4+}$ superexchange. Our results establish a pathway to interface-engineered ferromagnetic insulating phases via competing interactions, with potential for spin-insulatronic applications.
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All authors Nandana Bhattacharya, Ranjan Kumar Patel, Siddharth Kumar, Sourav Chowdhury, Manav Beniwal, Suresh Chandra Joshi, Prithwijit Mandal, Jayjit Kumar Dey, Weibin Li, Manuel Valvidares, Zhan Zhang, Hua Zhou, Andrei Gloskovskii, Christoph Schlueter, Christoph Klewe, Srimanta Middey

Strongly Correlated Electrons

Spin-Selective Spectral Flattening and Wave-Packet Dynamics in a Flux-Engineered Lieb Lattice

Nana Chang, Xiaoji Zhou, Yanglin Zhou et al. (+1 more)

We investigate reversible internal-state-selective wave-packet transport induced by spin-dependent Peierls phases in a two-dimensional nearest-neighbor Lieb lattice. The two conserved spin components experience effective fluxes $\alpha_{\sigma}=\alpha_{0}+s_{\sigma}\alpha_{s}$, where $s_{\uparrow,\downarrow}=\pm1$. At the working point $\alpha_{0}=\alpha_{s}=1/4$, the spin-up and spin-down components experience $\alpha_{\uparrow}=1/2$ and $\alpha_{\downarrow}=0$, respectively. A band-resolved calculation in the $q=2$ magnetic unit cell shows that the spin-up spectrum contains two zero-energy flat subbands associated with the sublattice-imbalance flat-band sector, whereas the remaining four subbands retain finite bandwidths. The half-flux sector therefore fails the all-bands-flat condition and does not realize exact Aharonov–Bohm caging for a generic localized initial state. Nevertheless, real-time simulations reveal a pronounced suppression of spin-up propagation relative to the dispersive spin-down component, manifested by a smaller mean-square displacement and an enhanced finite-region retention probability over the pre-reflection time window. Reversing the state-dependent flux interchanges the slow and fast spin channels, while the dynamical contrast remains robust against moderate flux detuning. These results establish spin-dependent synthetic flux as a reversible means of controlling internal-state-resolved matter-wave transport without spin-flip processes or interactions, and provide complementary spectral and real-space criteria for distinguishing exact caging from finite-time dynamical slowing in atomic and photonic flat-band simulators.
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All authors Nana Chang, Xiaoji Zhou, Yanglin Zhou, Song Ci

Strongly Correlated Electrons · Cross-listed from physics.chem-ph

Projected q-Shells for Nested Gausslet Bases

Steven R. White

Electronic-structure calculations require a finite representation of both the electronic wave functions and their Coulomb interaction. Conventional compact basis sets lead to a four-index interaction. Gausslet basis sets are one of a very small number of approaches that allow a much smaller two-index interaction, similar to a real-space grid, but with far fewer points. The continuing challenge in their development is reducing further the number of functions needed while maintaining high accuracy. Here we introduce projected q-shells (PQS), an improvement to the nested Cartesian gausslets of White and Lindsey. Their standard nesting construction divides a joining shell into disjoint faces, edges, and corners, reducing its polynomial completeness from order q to order q-2. PQS approximately restores the two lost orders. In terms of completeness, we prove that for an ideal, undistorted parent, the span of the PQS basis is equivalent to an overcomplete basis of overlapping patches. Coordinate distortions, which are always used in practice, harm this equivalence only slightly. The moment properties that allow two-index interactions also become inexact, even without distortion, but we show that the improvement in order more than makes up for this loss. For similar basis sizes, PQS gives smaller one-electron and interaction errors on small molecules, such as H2+, H2, and C2, than standard nesting. The improvement is largest for more compact bases with smaller q.
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Strongly Correlated Electrons

Orbital-Selective Coexistence of Interlayer Spin-Singlet Formation and SDW Order with Anomalous Spin Reconfiguration in Bilayer Nickelate La$_{3}$Ni$_{2}$O$_{7}$ Revealed by $^{17}$O-NMR

H. Lee, M. Yashima, M. Kakoi et al. (+7 more)

The spin structure of the spin density wave (SDW) order in the bilayer nickelate La$_3$Ni$_2$O$_7$ has been investigated using site-selective $^{17}$O-NMR measurements on the inner apical O(1), outer apical O(2), and planar O(3,4) sites. Below $T_{\rm SDW}$ (= 150 K), the peak of all planar O(3,4) sites significantly broadens due to the emergence of a finite internal magnetic field, whereas O(2) sites remain with no (or a negligibly small) internal field. These results are consistent with commensurate SDW order with a single spin-spinless (or large-tiny spin) stripe. As for the O(1) sites that bridge the NiO$_2$ planes, the internal field is nearly canceled below $T_{\rm SDW}$, indicating an antiparallel spin configuration between adjacent planes. However, below $T_\text{A}$ ($\sim$ 115 K), the spectrum of the O(1) site disappears even though the in-plane SDW order remains robust, implying that the antiparallel spin configuration through the Ni–O(1)–Ni bond is not particularly stable below $T_{\rm A}$, despite the expected strong interlayer spin coupling between the NiO$_2$ planes. Above all, we emphasize that the local spin susceptibility is extremely small at the O(2) site that has a strong covalency with the $d_{3z^2-r^2}$ orbital, indicating a well-developed interlayer spin-singlet formation in the Ni-$d_{3z^2-r^2}$ orbitals bridging the NiO$_2$ planes. These findings shed new light on the interlayer spin-singlet formation and the anomalous spin reconfiguration through the $\text{Ni--O(1)--Ni}$ bonding orbitals connecting the NiO$_2$ planes, which characterize the orbital-selective nature of the bilayer nickelate La$_3$Ni$_2$O$_7$.
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All authors H. Lee, M. Yashima, M. Kakoi, T. Ino, Y. Arai, K. Kitagawa, H. Sakurai, Y. Takano, K. Kuroki, H. Mukuda

Strongly Correlated Electrons · Cross-listed from physics.comp-ph

Vectorized Symmetric and Fermionic Tensor Network Implementations for GPU-Accelerated Variational Monte Carlo

Si-Jing Du, Johnnie Gray, Ao Chen et al. (+1 more)

Variational Monte Carlo (VMC) calculations based on tensor networks (TN) have recently achieved competitive accuracy in ground-state calculations of strongly correlated spin and fermionic systems. However, existing tensor network VMC (TN-VMC) algorithms have not been formulated in a manner that can fully utilize GPU acceleration. We tackle the key missing ingredient, namely, the vectorized evaluation of tensor network amplitudes and tensor network operations. This ensures high GPU utilization by batching over computations with identical structure. In particular, we show how to achieve vectorization for the practically relevant case of abelian symmetric tensor networks (which includes fermionic tensor networks) by developing a “flat” tensor network formalism for block-sparse tensor representation and contraction. Using this, we construct a GPU-adapted symmetric TN-VMC workflow with batched tensor network computation. In the two-dimensional Fermi–Hubbard model, we demonstrate a GPU speedup of up to $300 \times$ over single core CPU implementations, for fermionic TN variational wavefunctions.
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All authors Si-Jing Du, Johnnie Gray, Ao Chen, Garnet Kin-Lic Chan

Thursday 27 August

Strongly Correlated Electrons · Cross-listed from math-ph

Fractional Hall Conductance of Laughlin States from a Topological Index

Sven Bachmann, Severin Schraven, Jacob Shapiro et al. (+1 more)

We provide a rigorous Laughlin-pump argument that establishes the fractional quantization of the Hall conductance directly from the Laughlin state as a topological index. Our proof uses a recently defined index of a pair of pure states together with an infinite matrix product state analysis that is rigorous on a sufficiently thin cylinder. By virtue of the connection to an index, our result implies, in particular, that Laughlin states are representatives of topologically stable fractional quantum Hall phases.
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All authors Sven Bachmann, Severin Schraven, Jacob Shapiro, Simone Warzel

Strongly Correlated Electrons · Cross-listed from quant-ph

Pulling strings in real time: flux tube dynamics in (2+1)-d $\mathbb{Z}_2$-Higgs Gauge Theories

Zeno Bacciconi, Martina Frau, Luca Tagliacozzo et al. (+2 more)

Understanding real-time flux-tube dynamics in more than one spatial dimension is key to unlocking the non-perturbative physics of confinement, and is now actively pursued by quantum computing and simulation experiments. However, describing such dynamics has proven to be extremely challenging with both experiments and state-of-the-art numerical simulations limited to small volumes and short timescales. Here we investigate flux tube statics and real-time evolution in a genuine two-dimensional $\mathbb{Z}_2$ Higgs gauge theory at system sizes and timescales order of magnitude beyond present experiments and numerics. The key enabling element is the recently introduced Clifford-augmented matrix product states (CAMPS) framework, which we demonstrate to parametrically reduce the entanglement that must be represented in the matrix product state; both in the pure-gauge limit and in the presence of dynamical matter. We benchmark this capability through stringent tests of effective string theory, including universal spectral features and flux tube roughening properties in presence of matter. We then introduce a string-pull protocol that selectively excites transverse modes and reconstructs their finite-size spectrum in real time. In the rough regime, the response is collective, and our simulations show that this is also well captured by universal effective string theory predictions. Strong confinement instead produces long-lived, lattice-locked local dynamics persisting to times $tJ \gtrsim 100$. These results provide ab initio evidence that effective string theory captures nonequilibrium string dynamics and reveal a hitherto unexplored long-lived prethermal regime of strongly confined flux tubes, providing a novel angle on how confinement dictates dynamics in more than one spatial dimension.
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All authors Zeno Bacciconi, Martina Frau, Luca Tagliacozzo, Michele Caselle, Marcello Dalmonte

Strongly Correlated Electrons · Cross-listed from quant-ph

Spectral Fingerprints of Gauge Theories on a Quantum Computer

Graham Van Goffrier, Debasish Banerjee, Bipasha Chakraborty et al. (+1 more)

Maximally mixed state spectral sampling is an unbiased quantum algorithm that allows for extraction of a finite-resolution spectral distribution from a Hamiltonian over potentially the entire allowed range of energies. We show how it may be focused on any desired area of the spectrum in order to learn about the full fingerprint of the model of interest: from its ground state phenomena such as quantum criticality, obtained from the lowest lying energies, to its thermalization behavior, obtained from the mid-spectrum. We demonstrate this technique specifically on a $(1+1)d$ non-Abelian $SO(3)$ gauge theory, providing a comprehensive analysis of the steps necessary for performing this algorithm, as well as what is possible in the near-term with superconducting quantum hardware, performing simulations with circuits that are $78$ two-qubit gates deep. We show how this algorithm is able to take advantage of emerging dynamical circuit capabilities in near-term hardware to roughly halve the number required qubits, as well as how quantum readout error mitigation is trivial for this method. Along the way, we propose a novel strategy for compiling the controlled-time evolutions needed for spectral sampling by means of Pauli-frame optimizations. We illustrate two physical applications of quantum spectral sampling – disordered many-body transitions, and mid-spectrum densities of states – and what postprocessing steps they require beyond the Fourier outputs of the algorithm.
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All authors Graham Van Goffrier, Debasish Banerjee, Bipasha Chakraborty, Emilie Huffman

Strongly Correlated Electrons

Metallogenic quantum criticality: Fermi surface nucleation at transitions between gapped phases

Zhengyan Darius Shi

Continuous quantum phase transitions in interacting many-body systems exhibit universal phenomena that are largely independent of microscopic details. An organizing principle distilled from canonical examples such as the magnetic transition in Ising models is that the low-energy physics of transitions between gapped phases is governed by scale-invariant quantum field theories with gapless degrees of freedom at isolated points in momentum space. In this paper, we show that this principle can fail in a radical way: an entire gapless Fermi surface can emerge at a quantum critical point separating two fully gapped insulators. These exotic phase transitions are dubbed metallogenic quantum critical points (MGQCP). We construct a controlled family of effective field theories for MGQCPs between distinct fractional Chern insulators and propose a periodically modulated quantum Hall bilayer as a minimal microscopic setting. The critical theory exhibits an unusual mixture of physical signatures: while transport and compressibility follow scaling laws compatible with a conformal field theory, the electron spectral function develops a power-law non-analyticity at the Fermi momentum, characteristic of non-Fermi-liquid metals. We discuss how the concept of MGQCP may shed new light on critical phenomena in moire materials with tunable Chern bands. More generally, our results point to a broader class of quantum critical phenomena in which extended manifolds of gapless excitations emerge in momentum space despite being absent in both neighboring phases.
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Strongly Correlated Electrons

Exact Stiffness and Dynamical Responses from Fock-Space Fragmentation

Jonah Herzog-Arbeitman, Eslam Khalaf and Zhaoyu Han

Exactly solvable quantum many-body models are rare, and even when their spectra are algebraically organized, dynamical responses generally remain difficult to obtain because they probe an extensive number of excited states. Here we show that quantum geometric nesting (QGN) models admit an unusually strong form of solvability rooted in Fock-space fragmentation: excitations on top of the exact frustration-free ground states decouple into Krylov subspaces with a fixed number of particle and hole operators, and hence remain dynamically invariant. Exploiting this structure, we prove that the stiffness of the spontaneously broken continuous symmetry in QGN models is exactly equal to its variational value in the Gaussian manifold, confirming a conjecture from quantum many-body bootstrap~\cite{GaoHanKhalaf2026}. The proof shows that an infinitesimal phase twist couples the ground state only to the one-particle, one-hole fragment, which coincides with the tangent space of the ground state within the variational manifold, thereby making the variational curvature exact. More generally, perturbations whose action remains within a fixed Fock-space fragment have response functions determined exactly by the corresponding few-body sector, enabling exact access to quantities including static susceptibility, optical conductivity, dynamical structure factors, and single-particle Green's functions.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall

Band's Geometry Origin of Quantum Spin Transport Phenomena

Elena Derunova and Mazhar N. Ali

We develop a geometric description of spin-dependent transport based on the local geometric structure of electronic bands and the Fermi surfaces. For quasi-two-dimensional systems, we show that hyperbolic regions of constant-energy surfaces generate a geometrical contribution to the Fermi velocity that couples naturally to electron spin and produces a spin-current response. We further show that, in the presence of time-reversal symmetry, the algebra of spin operators can be related to the exterior algebra of the band's tangent space, providing an additional geometric interpretation of spin in momentum space. This framework motivates a symplectic description of spin-separated transport on Fermi surfaces and its extension to three-dimensional band manifolds through contact geometry. Our results establish a direct connection between Fermi-surface geometry and intrinsic spin transport.
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Strongly Correlated Electrons

A continuous confinement-deconfinement transition in a triangular quantum magnet

Suguru Hosoi, Sejun Park, Michihiro Hirata et al. (+13 more)

A continuous transition between phases hosting distinct excitations—bosonic magnons versus fermionic spinons—is a long-sought phenomenon in quantum magnetism, analogous to the confinement–deconfinement transition in quantum chromodynamics. We report evidence for such a transition in the triangular-lattice antiferromagnet TlYbS$_2$. Antiferromagnetic order develops below $T_\mathrm{N} \approx 0.53\,\mathrm{K}$. A $c$-axis field suppresses this order, driving the system into a gapless quantum spin liquid with a spinon Fermi surface above $\mu_0 H_\mathrm{c} \approx 3\,\mathrm{T}$, evidenced by a finite residual linear term in thermal conductivity, a Pauli-like susceptibility, and a temperature-independent NMR Knight shift. Approaching $H_\mathrm{c}$ from above, the scattering rate of itinerant excitations is strongly enhanced while their density of states shows no critical enhancement, atypical of conventional magnetic quantum criticality. These results point to a continuous confinement–deconfinement transition governed by fractionalized excitations beyond the Ginzburg–Landau paradigm.
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All authors Suguru Hosoi, Sejun Park, Michihiro Hirata, Minseong Lee, Adam P Dioguardi, Joe D Thompson, Filip Ronning, Allen O Scheie, Kumpei Imamura, Kenichiro Hashimoto, Takasada Shibauchi, Bishnu P Belbase, Arjun Unnikrishnan, Johannes Knolle, Arnab Banerjee, Yuji Matsuda