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Physics Condensed Matter Strongly Correlated Electrons

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Wednesday 14 October · still arriving

Strongly Correlated Electrons

Metallic electron crystals in rhombohedral graphene as a bridge to twisted WSe$_2$

Wentai Deng, Chenyuan Li, Naoto Nakatsuji et al. (+4 more)

Superconducting phases have recently been discovered both in twisted bilayers of transition metal dichalcogenide WSe$_2$ (tWSe$_2$) and in rhombohedral multilayer graphene (RMG). While both have generated extensive interest, they appear to be driven by qualitatively different physics. Here, we propose a unified picture in which the superconductivity in RMG arises from a strongly correlated metallic state with a spatial length scale that is compatible with the moiré length scale of tWSe$_2$. Central to this mechanism is a Wigner crystal phase in RMG that is metallic, driven by a "W"-shaped dispersion in the flat part of the underlying graphene band structure. We demonstrate this effect through calculations of Wigner crystal states in pentalayer RMG, focusing on dilute electrons in the quarter-metal regime relevant to experiment. In a region of the phase diagram we find the Wigner crystal breaks three-fold rotation symmetry, which guides our construction of a $t$-$V$ model on a triangular lattice as an effective description of the low-energy electronic physics. This construction suggests a surprisingly similar low-energy description of RMG and tWSe$_2$. Broader implications for superconductivity in dilute carrier systems are also discussed.
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All authors Wentai Deng, Chenyuan Li, Naoto Nakatsuji, Fang Xie, Lei Chen, Qimiao Si, Jennifer Cano

Strongly Correlated Electrons

Anyons at impurities: Fractional charge measurement and "wrong sign" binding

Haydn S. Adlong, Arthur Christianen, Atac Imamoglu et al. (+1 more)

Recent photoluminescence experiments in twisted MoTe$_2$ have reported signatures of anyons binding to trapped trions. The measured binding energies near the fractional Chern insulators at fillings of $\nu=-2/3$ and $-3/5$ have a ratio close to the fractional-charge ratio $5/3$, even though such scaling is not generally guaranteed for the expected short-range trion-anyon interaction. We model the trapped trion as a fixed impurity, and investigate anyon-impurity binding using a lowest-Landau-level model with exact diagonalization and Jain wavefunctions. Surprisingly, we find that the anyon-impurity binding energy ratio between $\nu=-2/3$ and $-3/5$ is close to $5/3$ for either short- or long-ranged impurity-electron interactions. However, the ratio departs strongly from the charge ratio at intermediate ranges or different Jain states. Remarkably, we also uncover "wrong-sign" binding, whereby both quasiholes and quasiparticles can bind to either sign of a short-range impurity potential by selecting orbital channels with favorable local density oscillations. Our findings show that localized excitons or trions can be used to probe the internal density profile of anyons.
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All authors Haydn S. Adlong, Arthur Christianen, Atac Imamoglu, Glenn Wagner

Strongly Correlated Electrons

Large-Tiny Spin-Stripe SDW Order in La$_3$Ni$_2$O$_7$ via $^{139}$La-NQR Spectroscopy: Reconsideration Based on the $Am2m$ Structure

Mitsuharu Yashima, Hongnam Lee, Takumi Ino et al. (+5 more)

The lower-symmetry $Am2m$ structure was recently proposed as the intrinsic ambient-pressure phase of La$_3$Ni$_2$O$_7$ based on synchrotron x-ray diffraction, whereas earlier studies investigated its properties assuming the commonly accepted $Amam$ structure. Here, we reexamine the crystal structure in La$_3$Ni$_2$O$_7$ and the spin configuration of spin-density-wave (SDW) state via $^{139}$La nuclear quadrupole resonance (NQR). The observation of two distinct La(2) sites in the NQR spectra is naturally accounted for by the $Am2m$ structure without any special assumptions, whereas it cannot be reconciled within the $Amam$ framework. Within the $Am2m$ framework, we reanalyze the spin configuration of the SDW phase and identify it as a large-tiny spin-stripe structure, arising naturally from two inequivalent Ni sites with large and tiny magnetic moments. These results establish the itinerant nature of the SDW order at ambient pressure in La$_3$Ni$_2$O$_7$, providing a basis for understanding its relationship to the emergence of high-$T_c$ superconductivity under high pressure.
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All authors Mitsuharu Yashima, Hongnam Lee, Takumi Ino, Nina Seto, Masataka Kakoi, Hiroya Sakurai, Yoshihiko Takano, Hidekazu Mukuda

Strongly Correlated Electrons

Influence of the Néel vector on the bulk electronic structure of MnTe measured from the $(1 \bar1 00)$ surface

D.A. Usanov, A.B. Hellenes, S. Hahn et al. (+7 more)

Altermagnetism gives rise to momentum-dependent spin splitting without net magnetization. Here, we use angle-resolved photoemission spectroscopy (ARPES) to investigate bulk $\alpha$-MnTe single crystals cleaved along the $(1\bar{1}00)$ plane - an orientation that preserves the compensated magnetic symmetry at the surface and substantially reduces surface effects and $k_z$ broadening. We resolve the three-dimensional bulk band structure with markedly enhanced spectral clarity. The $d$-wave band splitting, driven by the altermagnetic order and spin-orbit coupling in the $\mathbf{\Gamma}-\mathbf{K}-\mathbf{M}$ nodal plane, shows a perfect match to theoretical predictions. We further establish that the valence-band maximum occurs near the $\mathbf{A}$ point, identifying the corresponding hole pockets as the states governing the transport properties. Spatially resolved measurements reveal systematic variations of the band dispersion along $\mathbf{\Gamma}-\mathbf{K}$ and $\mathbf{A}-\mathbf{L}$, associated with different pinning of the Néel vector at the surface. Our results establish a surface-sensitive route to resolving the bulk altermagnetic electronic structure of MnTe and provide direct spectroscopic evidence for Néel-vector-dependent band splitting.
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All authors D.A. Usanov, A.B. Hellenes, S. Hahn, M. Leandersson, J. Osiecki, K. Uhlířová, D. Evtushinsky, L. Šmejkal, T. Jungwirth, J.H. Dil

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

Bulk superconductivity in quintuple-layer square-planar nickelate La6Ni5O12

Mengzhu Shi, Mei Du, Hongyu Li et al. (+5 more)

Nickelate superconductors, sharing a similar electronic environment with cuprate superconductors, offer a promising platform for unraveling the mechanism of high-temperature superconductivity. However, the realization of superconductivity in these systems has so far been restricted to thin films or bulk samples under high-pressure. This limits the applicability of various experimental probes to study the mechanism of superconductivity, and hinders the potential application of the nickelate superconductors. Exploring bulk superconductivity at ambient pressure is therefore essential to understand its origin and enable broader experimental research. Here, we report the realization of bulk superconductivity at ambient-pressure in quintuple-layer square-planar (SP) nickelate La6Ni5O12. The SP phase is obtained by performing topotactic reaction on the quintuple-layer Ruddlesden-Popper (RP) compound La6Ni5O16. Optimized reduction condition endows La6Ni5O12 with a superconducting state that exhibits onset transition temperature of ~ 18 K, as verified by both zero resistance and diamagnetic shielding effect. Pronounced hysteresis loops revealed by magnetization and torque magnetometry demonstrate the occurrence of vortex pinning. Specific heat measurements on a polycrystalline pellet of La6Ni5O12 reveal a clear superconducting transition at ~18 K and a superconducting volume fraction of ~ 25%, which strongly supports the presence of bulk superconductivity. Our results establish an unprecedented bulk sample platform for investigating superconductivity in nickelates at ambient pressure, which paves the way for further experimental studies into the superconducting mechanism.
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All authors Mengzhu Shi, Mei Du, Hongyu Li, Zhiwei Wang, Zhengjie Wang, Ziji Xiang, Tao Wu, Xianhui Chen

Strongly Correlated Electrons · Cross-listed from physics.optics

Near-field contributions to cavity-mediated radiative heat transfer

Antonio Mastropasqua, Martin Eckstein, Daniele Fausti et al. (+1 more)

Embedding materials in optical cavities has emerged as a powerful strategy for controlling their physical properties. In this context, increasing attention has been devoted to the thermal Purcell effect, which describes how the radiative heat transfer between a material and its photonic environ- ment can be modified by the electromagnetic boundary conditions imposed by the cavity. Here, we investigate near-field effects in cavity-mediated radiative heat transfer in planar cavities composed of realistic, dissipative gold mirrors, extending previous work that considered ideal mirrors. We iden- tify the conditions under which near-field effects lead to a substantial enhancement of heat transfer between the material and a photonic thermal bath relative to free space, owing to the strong modi- fication of the photonic local density of states by evanescent modes within the cavity. In particular, we find that radiative heat flow can be enhanced by several orders of magnitude in cavities ranging from nanometer to micrometer scales, depending on the absorber frequency and dipole orientation. These findings suggest that near-field effects may be relevant to polariton chemistry experiments and other systems operating within this cavity length-scale regime. Our results add to the idea that cavities can modify material properties not only by engineering vacuum fluctuations in the strong light-matter coupling regime, but also by controlling radiative dissipation and heat transfer.
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All authors Antonio Mastropasqua, Martin Eckstein, Daniele Fausti, Francesca Fassioli

Strongly Correlated Electrons

Disorder-Induced Griffiths like Phase and Charge Localization in Sr2FeRuO6

Koustav Pal, Shuvendu Ghosh and I. Das

A comprehensive understanding of complex transition-metal oxides is key to designing next-generation spintronic materials with tailored magnetic and transport functionalities. We investigate the interplay among structural disorder, frustrated magnetism, and localized charge transport in the 3d-4d hybrid double perovskite Sr2FeRuO6. The compound adopts a monoclinic structure with significant B-site antisite disorder that drives its unconventional behavior. Magnetic measurements uncover a robust Griffiths phase extending well above the ordering temperature, evidencing stable short-range ferromagnetic clusters within a disordered matrix. Electrical transport remains strongly localized, transitioning from small-polaron hopping at high temperatures to variable-range hopping at intermediate temperatures. These results position Sr2FeRuO6 as a representative 3d-4d hybrid system in which quenched disorder stabilizes spin inhomogeneity, while polaronic and hopping transport are also observed.
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Strongly Correlated Electrons · Cross-listed from cond-mat.dis-nn

Deep Learning of Phase Transitions for Bilinear-Biquadratic Spin-1 Chains from Correlation Aspects

Ming-Chiang Chung, Yu-Ting Kuo, Ian McCulloch et al. (+1 more)

We investigate the role of different correlation functions in reconstructing the phase diagram of the spin-1 bilinear-biquadratic chain, parametrized by the angle $\theta$ between the bilinear and biquadratic couplings, using our previously developed label-free machine-learning pipeline \cite{Ming21, Ming23}, in which an autoencoder compresses iDMRG correlation matrices into latent features and K-means clustering with silhouette analysis groups them into phases. Without any prior labels, the scheme reveals four natural phases, the Haldane, dimerized, critical trimerized, and ferromagnetic phases, and accurately locates the Takhtajan-Babujian ($\theta=-\pi/4$), $SU(3)$-symmetric Uimin-Lai-Sutherland ($\theta=\pi/4$), and Ferro-Dimer ($\theta=5\pi/4$) transition points; a shallow supervised refinement further sharpens the phase boundaries. We find that different correlation functions play fundamentally different roles in phase identification. The $SU(3)$-symmetric correlation alone selects a four-cluster partition that can be associated with the four phases, whereas the spin-spin and dimer-dimer correlations must be combined to recover the complete phase diagram. In contrast, the trimer-trimer correlation behaves as a marginal correlation: it is insufficient for phase identification by itself but improves the precision of the predicted phase boundaries when combined with the other correlations. Furthermore, the latent representations and silhouette values reveal signatures that we relate to the $\theta$ dependence of the correlations within each phase and, tentatively, to the underlying renormalization-group structure. These results demonstrate that machine learning can not only identify quantum phases but also uncover the physical information encoded in different correlation functions.
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All authors Ming-Chiang Chung, Yu-Ting Kuo, Ian McCulloch, Yuan-Hong Tsai

Strongly Correlated Electrons · Cross-listed from quant-ph

Majorana Edge Modes Reshape Kibble-Zurek Scaling in Kitaev Honeycomb Ribbons

Hyesung Choi, Antonio Mandarino and Mahn-Soo Choi

Recent progress in programmable quantum simulators motivates exact benchmarks for nonequilibrium dynamics in topological quantum matter. We study the Kitaev honeycomb model driven through its critical regions by a linear ramp of the bond coupling $J_z$ over a ramp time $\tau$, comparing zigzag and armchair ribbons with fully periodic tubes. The production of excitations exhibits a geometry-dependent finite-size crossover controlled by $N_2/\sqrt{\tau}$, the ratio of the ribbon width to the Kibble–Zurek length. Periodic tubes obey the expected critical-line Kibble–Zurek scaling and serve as the boundary-free benchmark. Zigzag ribbons follow the same scaling until defect production is exponentially suppressed by a finite-width algebraic gap floor associated with the formation of Majorana edge modes, whose occupation is pinned by inversion parity. Armchair ribbons instead support transient Majorana edge modes with exponentially small gaps, producing width-parity-dependent defect plateaus: exactly one defect per unit length for odd widths and an approximate, transient plateau near one half for even widths. The quench-generated entanglement entropy and fermionic logarithmic negativity inherit the same geometry-dependent structure, and the negativity further distinguishes the coherence-borne entanglement of the Kibble–Zurek regime from the population-borne entanglement of the edge-mode plateaus. These results identify boundary Majorana modes as the mechanism controlling departures from ideal Kibble–Zurek dynamics and provide geometry-resolved benchmarks for programmable simulations of topological matter.
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Strongly Correlated Electrons

Interplay of electric field and electronic correlations in pairing competition in bilayer nickelates

Yanmei Cai, Yicheng Xiong, Ying Liang et al. (+1 more)

Layer polarization provides a means of tuning the competition between interlayer and intralayer pairing in bilayer nickelates. Using ground-state constrained-path quantum Monte Carlo, we study interlayer $s^{\pm}$ and intralayer $d$ pairing in a bilayer two-orbital Hubbard model with a layer potential-energy difference $\varepsilon$ representing an effective perpendicular electric field. Within the parameter range studied, increasing $\varepsilon$ generally enhances the finite-size pairing vertex contribution $V_d$ and reduces $V_{s^{\pm}}$, shifting the relative pairing preference toward the $d$-wave channel. Increasing the onsite repulsion enhances both vertex contributions, more strongly in the $d$-wave channel, whereas increasing the crystal-field splitting reduces both and makes $s^{\pm}$ pairing relatively more competitive. Hund's coupling increases the relative competitiveness of $s^{\pm}$ pairing at weak bias, while enhancing the relative strength of $d$-wave pairing at large bias. The bias primarily redistributes charge between layers within each orbital sector, accompanied by an increase in the antiferromagnetic spin structure factor. Hund's coupling also enhances local interorbital parallel-spin correlations. These observations suggest possible connections between charge redistribution, magnetic correlations, and pairing competition, offering insight into how layer polarization and multiorbital interactions influence the relative pairing tendencies in the bilayer nickelate model.
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All authors Yanmei Cai, Yicheng Xiong, Ying Liang, Tianxing Ma

Strongly Correlated Electrons

Beyond Kitaev exchange: $\Gamma'$-driven magnetism in Ag$_3$LiRh$_2$O$_6$

Efrain Insuasti Pazmino, Shi Feng, Ramesh Dhakal et al. (+4 more)

In Kitaev magnets, frustration arises from bond-dependent spin anisotropic interactions, which can potentially realize sought-after quantum spin liquid phases. However, material realizations with dominating Kitaev exchange are scarce and the broad parameter space of extended Kitaev models remains largely unexplored experimentally. Here, we use density-functional theory, cluster many-body, spin-wave, and density-matrix renormalization calculations to show that the recently discovered honeycomb rhodate Ag$_3$LiRh$_2$O$_6$ hosts an off-diagonal exchange $\Gamma_1'$ that is second in magnitude only to the ferromagnetic Kitaev exchange $K_1$. This combination of $K_1$ and $\Gamma_1'$ explains key experimental observations, an unusually high magnetic ordering temperature of 94 K at ambient pressure and its rapid decrease under hydrostatic pressure as Ag$_3$LiRh$_2$O$_6$ evolves from ferromagnetic toward zigzag order within the honeycomb planes. Our spin-wave calculations further predict an unusual topology of the magnon bands arising from the $\Gamma_1'$ term in the spin Hamiltonian of the honeycomb layer. We show that the large trigonal splitting of $t_{2g}$ states enhances $\Gamma_1'$, the hitherto underappreciated term in Kitaev magnets, and opens the way to new interesting regimes of the extended Kitaev model.
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All authors Efrain Insuasti Pazmino, Shi Feng, Ramesh Dhakal, Ioannis Rousochatzakis, Stephen M. Winter, Johannes Knolle, Alexander A. Tsirlin

Strongly Correlated Electrons

Role of Gd 5d-Au 5d hybridization for the magnetic properties of Au-Al-Gd quasicrystal approximants

Goro Nozue, Hidenori Fujiwara, Satoru Hamamoto et al. (+18 more)

We have studied the electronic states of magnetic Au-Al-Gd quasicrystal approximants, which exhibit different magnetic ground states at low temperatures, by orbital-selective soft and hard x-ray electron spectroscopies in the paramagnetic phase. Our results reveal that the valence electronic states vary among the Au-Al-Gd approximants with different magnetic ground states, whereas the Gd 4f electrons are localized in all of them. In particular, we find that the Gd 5d states are hybridized with the Au 5d states around the Fermi level, providing information about a local pathway for the intersite exchange interaction between the localized Gd 4f electrons. This hybridization strength varies among these samples. Our findings bring an orbital-resolved microscopic picture to the magnetism of rare-earth-based quasicrystals and approximants.
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All authors Goro Nozue, Hidenori Fujiwara, Satoru Hamamoto, Yuto Torii, Mai Sakaguchi, Sho Nakajima, Takuya D. Nakamura, Nonoka U. Sakamoto, Takayuki Kiss, Masaki Oura, Akira Yasui, Kotaro Higashi, Naomi Kawamura, Kojiro Mimura, Arata Tanaka, Asuka Ishikawa, Farid Labib, Shintaro Suzuki, Takafumi D. Yamamoto, Ryuji Tamura, Akira Sekiyama

Strongly Correlated Electrons

Room-Temperature Metallic 2D Ferromagnetism Stabilized by Quantum Metric

Teng-Fei Ying, Jianqi Zhong, Songyuan Geng et al. (+3 more)

The recent discovery of long-sought dice-lattice bands in layered electride YCl opens up unprecedented opportunities for studying correlated electrons in real dice lattice systems. While the weakly dispersive band at the Fermi level is partially filled and density-wave states are expected due to Fermi surface nesting based on conventional theories, the ARPES measurement nevertheless revealed a uniform flat band splitting of 0.5 eV, suggesting unusual ferromagnetism (FM) borne out of the metallic 2D dice lattice. In this Letter, we propose that the uniform metallic FM order is stabilized by the prominent quantum metric near topological band crossing points at K and K', which reconstructs the magnetic instability in the dice metal and tips the density-wave instability toward a uniform FM order. Importantly, our analysis based on random phase approximation (RPA) and Hartree-Fock theory predicts a remarkably high Curie temperature above room temperature for the 2D FM order. These findings establish the first example of a room-temperature 2D metallic magnet stabilized by quantum metric, which not only exemplifies the fundamental significance of quantum geometry in solids but also bears far-reaching applications in energy-efficient high-density magnetic memories.
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All authors Teng-Fei Ying, Jianqi Zhong, Songyuan Geng, Fangjie Chen, Haoxiang Li, Benjamin T. Zhou

Strongly Correlated Electrons

Multiple Superconducting Phases under Pressure for Different Field Directions in UTe2

Dai Aoki, Atsushi Miyake, Ai Nakamura et al. (+7 more)

The existence of multiple superconducting phases is a striking feature of UTe2, arising from the spin and orbital degrees of freedom and supporting a spin-triplet superconducting state. We present field-temperature phase diagrams under pressure for fields applied along the three principal crystallographic axes, as determined by AC calorimetry measurements. The pressure evolution of the multiple superconducting phases is highly anisotropic with respect to magnetic field direction, revealing rich superconducting phenomena arising from complex fluctuations.
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All authors Dai Aoki, Atsushi Miyake, Ai Nakamura, Yoshiya Homma, Dexin Li, Shota Mizuno, Georg Knebel, Daniel Braithwaite, Jean-Pascal Brison, Jacques Flouquet

Strongly Correlated Electrons

Odd-to-Even-Layer Switch of Spontaneous Excitonic State in $\rm{TiSe_{2}}$ Thin Films

Kaili Wang, Zhuowei Liu, Yuyang Mu et al. (+8 more)

$\rm{TiSe_{2}}$ is a candidate of high temperature excitonic condensates with spontaneous exciton formation in addition to its charge density wave (CDW). However, direct observation and manipulation of this electron-hole paring state formation is still lacking. Here, using varying-temperature angle-resolved photoemission spectroscopy (VT-ARPES), we observe a distinct odd-to-even-layer switch of spontaneous exciton state formation with the evident correlated band structure in $\rm{TiSe_{2}}$ thin films. While the odd-layer $\rm{TiSe_{2}}$ films show a sharp band structure in single-particle picture superimposed by CDW renormalization, in the even-layer $\rm{TiSe_{2}}$ films, the full-filling valence band (VB) opens a distinct notch at the top, and the conductive band (CB) shows a significant extra signal extending above Fermi level with spectra broadening. These features indicate that the extra holes (notched VB) and electrons (broadening CB above Fermi level) form spontaneous excitons in even-layer $\rm{TiSe_{2}}$. Based on a correlated electron-hole model extracted from the tight-binding description, we reproduce the characterized band structures with spontaneous exciton formation, where the interlayer inter-band coupling in $\rm{TiSe_{2}}$ plays a key role, which leads to an odd-to-even-layer switch of the excitonic state formation. Our results provide direct evidences of the spontaneous exciton formation, promising an excitonic condensate as versatile platform for realizing Bose-Einstein condensate (BEC) and investigating novel correlated phenomena.
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All authors Kaili Wang, Zhuowei Liu, Yuyang Mu, Zhujuan Li, Zhenjie Fan, Yu Gui, Xiaodong Qiu, Baigeng Wang, Rui Wang, Yi Zhang, Qi-Kun Xue

Strongly Correlated Electrons

Evidence for hidden order and its potential correlation with electron-hole asymmetry in iridate superlattices

Zhihan Qiao, Han Zhang, Hangtian Wang et al. (+12 more)

Hidden order refers to an order that shapes the properties of quantum materials yet remains difficult to identify. Here we report signatures of a hidden order in doped iridate superlattices through an unexpected electron-hole asymmetry in the coupling between the insulating state and the antiferromagnetic (AFM) state. While carrier doping suppresses both states, they remain coupled in the electron-doped regime but decouple in the hole-doped regime. Structural analysis rules out octahedral rotation and tilting as the dominant origin of this asymmetry. Instead, magnetic characterization reveals evidences of a hidden order that only appears in the hole-doped regime. This hidden order emerges above TN and is closely associated with the AFM state, coinciding with an exceptionally strong magnetic scattering intensity and an anomalously robust magnetic coherence. Our results highlight that hole-doped iridates can be a promising platform for exploring hidden and unconventional ordering phenomena in spin-orbit-entangled quantum materials.
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All authors Zhihan Qiao, Han Zhang, Hangtian Wang, Deyang Li, Haiyang Zhang, Enyang Men, Junlei Jiang, Jingxin Chen, Yizhou Liu, Sang-Youn Park, Xiangnan Xie, MingLiang Tian, Haifeng Du, Ning Hao, Lin Hao

Tuesday 13 October · still arriving

Strongly Correlated Electrons

Signatures of symmetry-stabilized Dirac fermions in correlated oxide CaNbO3 thin films

Yunkyu Park, Seoung-Hun Kang, Jeongkeun Song et al. (+11 more)

Symmetry-protected electronic states in correlated oxides offer a route to combining topology, lattice tunability, and many-body interactions, but creating such topological electronic states in complex oxides remains challenging. Here, we show that oxygen octahedral rotations provide a symmetry-control parameter for stabilizing Dirac-related electronic states in epitaxial CaNbO3 films. By comparing compressively strained tetragonal films and relaxed orthorhombic films, we demonstrate that distinct octahedral rotation patterns preserve nonsymmorphic symmetry and lead to distinct transport signatures consistent with Dirac-like electronic states. The films exhibit metallic transport with high mobility of 138,000 cm2 V-1 s-1, multichannel conduction, and Shubnikov-de Haas oscillations from small high-mobility Fermi pockets. Landau-fan diagram analysis indicates finite Berry-phase contributions, while first-principles calculations reveal a strain-driven evolution from nodal-line band crossings in the orthorhombic phase to Dirac-electron band features in the tetragonal phase. These results establish oxygen octahedral symmetry as a design knob for engineering topological electronic states in correlated perovskite oxides.
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All authors Yunkyu Park, Seoung-Hun Kang, Jeongkeun Song, Minsik Kong, Seohee Kim, Shan Lin, Eun Sang Choi, Km Rubi, Hua Zhou, Sangmoon Yoon, Hu Miao, Satoshi Okamoto, Jong Mok Ok, Ho Nyung Lee

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

Atomic ironing for conformal interfaces in freestanding oxide nanomembranes

Jeongkeun Song, Keaghan Knight, Keun-Yeol Park et al. (+7 more)

Atomically well-defined interfaces are essential for realizing functional interlayer coupling in stacked and twisted oxide heterostructures, yet transferred freestanding oxides can develop structural inhomogeneities, including local curvatures, interfacial voids, and incomplete contacts with substrates. Here, we demonstrate that these transfer-induced structural disorders and imperfections evolve substantially and can be suppressed by post-transfer thermal treatments, yielding bulk-like crystalline freestanding oxide nanomembranes. Using freestanding SrTiO3 membranes as a model system, we report a systematic understanding of the role of "atomic ironing" and the associated evolution of lattice mosaicity, interfacial roughness, and optical bandgap. We further demonstrate atomically bonded conformal interfaces in twisted SrTiO3 heterostructures, highlighting the importance of post-transfer thermal processes. These results establish a synthetic strategy to restore the structural integrity and intrinsic bulk-like functionality of freestanding oxide nanomembranes, enabling stacked, twisted, and heterogeneously integrated oxide architectures with atomically well-defined interfaces for emerging quantum functionalities.
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All authors Jeongkeun Song, Keaghan Knight, Keun-Yeol Park, Young-Hoon Kim, Tyler J. Sachs, Hu Miao, Jiaqiang Yan, Celesta S. Chang, Ambrose Seo, Ho Nyung Lee

Strongly Correlated Electrons

Spectral signatures of spin textures and the emergence of a pseudogap

Matteo Quinzi, Andrea Pintus, Tommaso Chiarotti et al. (+2 more)

Periodic solids with strongly interacting electrons display phenomena – from Mott localization to high-temperature superconductivity – that escape conventional band theory. Efforts to address this unconventional physics have been typically cast in the language of Green's function theories and the associated frequency- and momentum-dependent self-energies capturing strong correlations beyond the reach of mean-field theories. Here, we underscore that frequency- and momentum-dependent self-energies emerge also from mean-field solutions that break translational symmetry, and that these self-energies can display the characteristic fingerprints of strong correlations for certain, physically meaningful, spatial patterns. We showcase this perspective by studying the paradigmatic case of the 2D Hubbard model. We find that already at the mean-field level the doped antiferromagnet displays, in addition to stripes, many quasi-degenerate self-consistent solutions with antiferromagnetic textures organized into antiphase domains separated by hole-rich interfaces, reminiscent of the phase-separation scenario. Remarkably, these solutions map into spectral functions that display very distinctively the phenomenology of the pseudogap, including the nodal-antinodal dichotomy of the self-energy, Fermi arcs, and a complementary Luttinger surface. The result is a conceptually simple description of such an intricate many-body state: the pseudogap emerges as the momentum-space spectral portrait of the real-space interplay between antiferromagnetic domains and the metallic interfaces, which echoes the role of spin-fluctuations identified by nonperturbative methods.
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All authors Matteo Quinzi, Andrea Pintus, Tommaso Chiarotti, Massimo Capone, Nicola Marzari

Strongly Correlated Electrons · Cross-listed from hep-th

Kinetic Equations and Turbulence in Large $N$ Vector and SYK-like Models

Vladimir Rosenhaus and Daniel Schubring

We apply large $N$ expansion techniques to derive kinetic equations for strongly coupled, far-from-equilibrium field theories with $O(N)$ symmetry. For large $N$ vector models, the quasi-classical approximation holds. Incorporating arbitrary momentum-dependent interactions, we show the dynamics obey the standard kinetic equation, with the scattering amplitude given by the retarded propagator of the auxiliary Hubbard-Stratonovich field. This has broad applications to systems like spin wave and Langmuir ion-acoustic turbulence. For large $N$ random coupling (SYK-like) models in $d$ dimensions, leading-order melon diagrams induce order-one propagator renormalization and finite spectral width. The corresponding kinetic equation, unlike those for standard weakly interacting systems, does not have a local-in-time collision integral. We find evidence for a stationary, scale-invariant infrared solution, revealing a potentially novel strong turbulence scaling exponent.
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Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci

Engineering Correlated Transparent Conductors via Metal-Insulator Transition Proximity

Amit Cohen, Nofar Tuval, Maria Baskin et al. (+5 more)

Transparent conductors are key functional materials in modern optoelectronic devices. Their performance is governed by an inherent trade-off between optical transparency and electrical conductivity. Correlated metallic oxides offer an attractive workaround to this compromise, where narrow partially-filled bands provide high conductivity, while the absence of visible-range transitions enables optical transparency. Despite this promise, transparency and conductivity remain coupled through carrier density and electronic coherence. Here, we use proximity to a metal-insulator transition (MIT) as a design principle for engineering this balance in correlated-oxide transparent conductors. Epitaxial Ti-substituted $SrVO_3$ films serve as a model platform where the optical window and metallicity are tuned simultaneously. We demonstrate and explain a systematic broadening of the optical window to regimes relevant for silicon photovoltaics. This gain is counterbalanced by carrier depletion and disorder, which drive the loss of coherent transport near the composition-driven MIT. A Haacke figure-of-merit analysis identifies the optimal composition range near the MIT, where the loss of metallic transport is accompanied by persistent near-Fermi-level spectral weight, indicating disorder-assisted localization together with correlation-driven spectral-weight redistribution. These findings establish proximity to an MIT as a general materials-design strategy, using electronic filling as a tuning knob for the transparency-conductivity balance in correlated-oxide transparent conductors.
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All authors Amit Cohen, Nofar Tuval, Maria Baskin, Tien-Lin Lee, Tom Tiwald, Scott A. Chambers, Sophie D. Beck, Lior Kornblum

Strongly Correlated Electrons · Cross-listed from math-ph

Anomalies, higher symmetries, and homotopy theory I: crossed precosheaves and a nonabelian Cech construction

Anton Kapustin and Shixiong Xu

Symmetries of a quantum field theory or a quantum lattice model are expected to be described not by a group but by a homotopy type, whose homotopy groups are the higher symmetry groups and whose Postnikov invariants encode 't Hooft anomalies. We propose a homotopy-theoretic definition of 't Hooft anomalies based on the structure of localized symmetries in the operator-algebraic approach. The input is a crossed precosheaf: a collection of groups attached to regions of space, equipped with pairings recording that the commutator of two transformations localized in two regions is localized in their intersection. To a crossed precosheaf and a finite family of regions we attach a pointed connected homotopy type, the Cech-Loday classifying space. As the family of regions ranges over finite covers of space, the classifying spaces form a pro-object in the homotopy category. There is a canonical map from the ordinary classifying space of the symmetry group to this pro-type. Composing this map with a group action gives an anomaly whose nontriviality obstructs gauging. In favorable cases, the Cech-Loday space is essentially independent of the cover. In such cases, the homotopy fiber of the canonical map is a candidate for the classifying space of the higher group of symmetries. We give examples of crossed precosheaves arising from gauge transformations in continuum field theory and from quantum cellular automata and finite-depth circuits. For quantum spin systems in one and two dimensions, our construction recovers the Else-Nayak index and its generalizations to two dimensions.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Instability of Markov chains under infinitesimal coherent dissipation

Amir-Reza Negari, Yijian Zou and Timothy H. Hsieh

Under local Lindbladian evolution, the growth of conditional mutual information and its associated Markov length scale is not limited by Lieb-Robinson bounds, yet it has been unclear how quickly the Markov length can increase. We show that an arbitrarily short, strictly local Lindbladian can generate infinite Markov length from a product state. We also construct strictly local Lindbladians that converge rapidly to steady states with algebraically decaying conditional mutual information. Despite their long-range conditional correlations, the states we construct are local reversibly connected to a product state by sublinear depth circuits. Thus infinite Markov length does not imply slow relaxation nor obstruct phase stability when suitably defined.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Programmable Polaron Models and Tomography in Trapped-Ion Quantum Simulators

Filip Marijanovic, Utso Bhattacharya, Abhishek Menon et al. (+3 more)

Strong coupling between mobile charge carriers or excitons and lattice vibrations gives rise to polarons: quasiparticles formed by charge carriers dressed by a cloud of phonon excitations. Polaron formation determines transport properties of systems ranging from transition-metal oxides and organic semiconductors to light-harvesting complexes. In excitonic systems that admit a hard-core boson description, mapping the excitations to pseudospins provides a natural framework for studying polaron physics, including the nonperturbative regime in which hopping amplitudes, phonon energies, and coupling strengths are comparable. Here, we propose a trapped-ion blueprint for realizing spin-phonon Hamiltonians with programmable spatial coupling between excitation density and phonon displacements, encompassing local Holstein and long-range Fröhlich-type interactions. To access strongly dressed quasiparticles whose bare spectral weight is suppressed, we introduce displaced Green's functions implemented through spin-dependent phonon displacements. Their spectral response reveals the polaron band spectrum, including binding energies and phonon-excitation sidebands, while spatially resolved measurements probe the structure of the phonon dressing cloud, providing a route to polaron tomography. We further complement this spectroscopy with direct and ancilla-assisted measurements of spin-phonon correlations that track the coupled dynamics of the excitation and its environment. These approaches connect the emergent quasiparticle spectrum to the microscopic buildup of its dressing cloud, enabling controlled studies of how the spatial range of coupling shapes polaron formation and mobility.
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All authors Filip Marijanovic, Utso Bhattacharya, Abhishek Menon, Visal So, Guido Pagano, Eugene Demler

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

Non-Abelian quantum Hall states at strong Landau level mixing: finding anyons with first-principles AI

Pierre-Antoine Graham, Ahmed Abouelkomsan and Liang Fu

Non-Abelian anyons, strange particles forming the basis of fault-tolerant topological quantum computing, are predicted to emerge in fractional quantum Hall states at even-denominator filling factors. Identifying which topological order is realized has proven to be a challenging problem that requires an accurate, non-perturbative treatment of realistic Landau level mixing, which has so far been missing from theoretical studies. Here we present the first complete solution of non-Abelian quantum Hall problem that includes all electrons and all Landau levels, for spin-polarized electrons at filling factor $\nu = 3/2$. We develop a momentum-resolved neural-network variational wave function, optimized solely on the microscopic Hamiltonian, which gives direct access to the topologically degenerate ground states. Without any physics input about the expected outcome, it discovers a degenerate ground-state manifold whose entanglement reveals anyons with quantum dimension $\sqrt{2}$, the hallmark of Ising-type non-Abelian order. By directly computing the overlap with trial wave functions, we further show that Landau level mixing favors the anti-Pfaffian over other candidate states. Our results demonstrate the power of neural-network wave functions in finding and characterizing non-Abelian anyons from first principles, in regimes of strong Landau level mixing, relevant to many recent experiments.
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Strongly Correlated Electrons

Measurement-induced criticality for non-Abelian anyons: The monitored golden chain

Zhaohui Zhi, Bo Han, Romain Vasseur et al. (+3 more)

Non-Abelian anyon chains whose interactions favor a single fusion channel host quantum critical ground states described by minimal-model conformal field theories (CFTs) protected by a topological symmetry. We show that their measurement-only counterpart, where non-commuting fusion charge measurements act locally on the anyons of a chain of $L$ sites, provides a fundamental example of a non-unitary CFT controlling a non-Abelian learning problem. Mapping the monitored dynamics to a random tensor network, we numerically find $1/L$ scaling Lyapunov gaps, logarithmic entanglement scaling with the chord length, and an effective central charge in the Shannon entropy of the measurement record. The conserved topological charge sharpens with dynamical exponent $z= 1$ and is learnable by a decoder on an $O(L)$ time scale. As the topological symmetry is a non-invertible symmetry of the $SU(2)_k$ anyon theories, we establish the monitored golden chain $(k=3)$ as a non-Abelian generalization of the weakly (Kramers-Wannier) self-dual quantum critical point of the toric code $(k=2)$, and the first of a family for $k\geq 3$.
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All authors Zhaohui Zhi, Bo Han, Romain Vasseur, Andreas W. W. Ludwig, Simon Trebst, Guo-Yi Zhu

Strongly Correlated Electrons · Cross-listed from quant-ph

Invertible subalgebras for chiral semion topological order

Yu-An Chen, Meng Sun, Nathanan Tantivasadakarn et al. (+2 more)

Chiral topological order is incompatible with strictly two-dimensional local commuting-projector Hamiltonians on finite-dimensional tensor-product Hilbert spaces. Invertible subalgebras (ISAs) provide an alternative framework. We construct an ISA supporting chiral semions, together with its anti-semion commutant, on a square lattice with one qubit per edge. We give explicit non-Pauli generators for both algebras and prove that together they generate all local operators on the Hilbert space. Starting from the $\mathbb{Z}_4$ toric code, we condense the boson $e^2m^2$ and identify the semion and anti-semion algebras. We then decompose each $\mathbb{Z}_4$ qudit into two qubits and use a finite-depth circuit to disentangle one qubit per edge fixed by the condensation constraints. Pumping the semion ISA along the $z$ direction defines an explicit three-dimensional non-Clifford quantum cellular automaton (QCA). We show that pumping eight times is equivalent to a translation followed by a finite-depth quantum circuit with ancillary qubits. We also give an explicit finite-depth circuit relating this construction to the semion QCA previously obtained from topological quantum field theory. A similar condensation construction yields a $U(1)_4$ ISA on a square lattice. Together with the semion and earlier odd-prime ISAs, finite stacking realizes every pointed Witt class of bosonic Abelian anyon theories. Finally, we extend both constructions to all spatial dimensions $d=4k{-}2$, with one qubit or $\mathbb{Z}_4$ qudit on each $(2k{-}1)$-cell for the semion or $U(1)_4$ ISA, respectively.
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All authors Yu-An Chen, Meng Sun, Nathanan Tantivasadakarn, Zongyuan Wang, Bowen Yang

Strongly Correlated Electrons

A hierarchy of exact lower bounds on the Laughlin spectral gap

Michael G. Scheer and Eslam Khalaf

We develop a bootstrap approach to deriving lower bounds on the spectral gap of the first Haldane pseudopotential Hamiltonian on the sphere with $N_\Phi$ flux quanta for arbitrary $N_\Phi$, including in the thermodynamic limit $N_\Phi \to \infty$. Our approach can in principle be generalized to pseudopotentials describing other model wavefunctions such as the Moore-Read state or Read-Rezayi sequence. Our approach is based on Knabe's observation that if $H$ is a Hamiltonian with ground state energy $0$ then the spectral gap is at least $\epsilon > 0$ if and only if $H^2 \succeq \epsilon H$. To show this inequality, we split $H^2$ into two parts, one that can be analytically bounded and another that can be bounded using a finite semidefinite program (SDP). Crucially, the size of this program is determined only by cutoff parameters, and the program depends on $N_\Phi$ only parametrically, allowing us to obtain numerically exact (up to solver precision) lower bounds on the gap. In order to turn these numerical bounds into mathematically rigorous bounds, we introduce an algorithm that can produce nearly-optimal exact feasible points for large rational SDPs. We additionally provide an algorithm that establishes the rank stability of the semidefinite program in the limit $N_\Phi \to \infty$ which is needed to certify the bound in the thermodynamic limit. Beyond establishing the Laughlin gap and revealing a potential method for deriving spectral gap lower bounds for other pseudopotentials, our work provides a general method for turning numerical semidefinite programming bounds into rigorous mathematical proofs, which may have wide applicability.
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Strongly Correlated Electrons · Cross-listed from cond-mat.stat-mech

Emergent Loop Geometry in Gauge-Equivariant Graph Neural Networks

Ali Rayat and Gia-Wei Chern

Gauge-equivariant graph neural networks generate ordered products of gauge links through local message passing, but the geometry of these internal structures is not captured by the receptive field alone. We investigate the statistical ensemble of closed lattice walks generated by recursive node- and edge-feature operations, independently of network training. Analytical and numerical results reveal a separation between rapid growth of contour length and much slower spatial expansion: deeper compositions generate increasingly long paths through repeated traversal of relatively compact regions. Loop expansions of fermionic observables provide a physical interpretation of this hierarchy, showing how spatial locality remains compatible with high-order dependence on nearby gauge fields. These findings identify complementary roles of network depth in extending spatial reach and enriching the representations constructed within that reach, providing a geometrical perspective on learning lattice gauge observables.
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Strongly Correlated Electrons

Superexchange coupling between a dilute Gd3+ probe and orphan spins in a valence-bond glass

Patrick Colgan, Artur Solodovnyk, Jeremy P. Carlo et al. (+1 more)

The valence-bond-glass state of the 4d^1 double perovskite Ba2YMoO6 combines Mo^5+ singlets with residual paramagnetic "orphan" spins whose coupling is hard to reach with bulk probes. We probe them by electron paramagnetic resonance of a dilute Gd^3+ ion on the Y^3+ site via broadband coplanar-waveguide transmission at 5 K. The isostructural nonmagnetic niobate Ba2YNbO6, doped with the same Gd^3+ probe, is a fixed-lattice control. The Gd^3+ linewidth nearly doubles in the magnetic host. Dipolar coupling to the sparse orphans is nearly an order of magnitude too weak; the excess is instead reproduced by a transferred f-d superexchange of J ~ 0.2 K, so the width is a static measure of orphan-spin coupling. The half-field (Delta m_S = +/-2) satellite collapses in the magnetic host, a dynamical dephasing channel, while the unchanged g-factor marks a zero-mean random internal field. Together the two channels probe the coupling and dynamics of valence-bond-glass orphan spins.
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All authors Patrick Colgan, Artur Solodovnyk, Jeremy P. Carlo, Scott Dietrich