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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 14 October · still arriving

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Dynamical Decoupling of Nonclassical States in a Biased-Noise Spin Qudit

Arjen Vaartjes, Namit Anand, Rocky Y. Su et al. (+16 more)

Encoding quantum information in $d$-dimensional systems (qudits) with $d>2$ offers appealing new directions for resource-efficient quantum computing. However, protecting the coherence of nonclassical qudit resource states remains an open challenge. Dynamical decoupling (DD) is a well-established technique for extending coherence, but its application to qudits is hindered by the quadratic scaling of the decoupling sequence overhead with the dimension $d$. As a result, demonstrations of qudit DD have so far been limited to low-dimensional qudits. Here, we show that noise-biased qudits enable a nontrivial reduction of this overhead, for example, from quadratic to linear. We perform qudit DD on a model $d=8$ qudit, the nuclear spin of an antimony donor in silicon. We benchmark DD performance on highly nonclassical states such as uniform superpositions, cat states, and Haar random states and measure coherence improvements up to a factor $5$ to $10$. For a spin-cat error correction code, continuous DD extends the coherence time of the logical superposition $|+\rangle_L$ to $225$~ms, compared to $19$~ms under free evolution and $85$~ms with a Hahn echo. This improvement shows that DD sequences tailored to a system's noise bias can significantly enhance the lifetime of encoded logical qubits.
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All authors Arjen Vaartjes, Namit Anand, Rocky Y. Su, Akram Youssry, Ritik Sareen, Jeffrey Marshall, Mark R. van Blankenstein, Danielle Holmes, Benjamin Wilhelm, Bibek Pokharel, Xi Yu, Laura A. O'Neill, Martin Nurizzo, Alexander M. Jakob, Fay E. Hudson, Kohei M. Itoh, Andrew S. Dzurak, David N. Jamieson, Andrea Morello

Soft Condensed Matter

Active Sculpting: morphodynamics of internally stirred active vesicles

Devadevan M M and Brato Chakrabarti

Active flows are often confined by soft, deformable boundaries that they can push against, reshape, and in turn get reorganized by. Motivated by this interplay, we combine theory and numerical simulations to analyze the morphodynamics of an elastic vesicle enclosing a dilute suspension of extensile active particles. We model the two-dimensional vesicle as a weakly extensible elastic ring with bending rigidity, immersed in a Stokesian fluid, and describe the confined active suspension using a kinetic theory. The vesicle and the suspension are coupled hydrodynamically, through the kinematic and dynamic boundary conditions at the interface, and energetically, through a single alignment interaction that simultaneously aligns active particles with the membrane and the membrane with the particles. We show that this interaction reduces to a weak-anchoring boundary condition familiar from passive liquid crystals and derive a closed-form quiescent equilibrium state in which the nematic order in the suspension organizes into a vortex with a +1 defect core. A stability analysis of this state predicts an ordered hierarchy of activity thresholds at which successive shape modes of the vesicle are destabilized, as well as a purely passive, anchoring-driven instability of floppy vesicles. Nonlinear simulations, performed with a volume-conserving immersed boundary method, reveal that each threshold crossing gives rise to a distinct emergent state: a static spindle with boundary-pinned defects, a rotor that tank treads against its own rotation, a fluctuating spinner, and a turbulent state in which the vesicle acts as a self-stirring compartment. Beyond demonstrating how boundary deformability sculpts, and is sculpted by, confined active matter, our results open the door to study hydrodynamic interactions between such active vesicles and to use membrane fluctuations as a probe of activity of suspensions.
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Soft Condensed Matter

Emergent medium-range order in amorphous silicon

Zhen Zhang, Stephen R. Elliott, Yujie Wang et al. (+1 more)

Medium-range order (MRO) is an important feature of amorphous materials, but its nature in terms of atomic arrangement has remained elusive. Here, using large-scale machine-learning-driven atomistic simulations of amorphous silicon, we probe the MRO of this archetypal network glass. By characterizing the structure in three dimensions, we reveal that the symmetry of the atomic arrangement around a central atom shows a crossover as a function of distance. At short distances, the structure is determined by local bonding constraints, which evolve from predominantly tetrahedral environments in low-density amorphous silicon to highly coordinated and strongly disordered local environments in very-high-density amorphous silicon. At larger distances, however, distinct cubic- and octahedral-symmetry patterns emerge in the three-dimensional atomic-density distribution, despite the absence of these symmetries at shorter length scales. We find that this crossover is accompanied by a quasi-periodic spatial organization of the topological rings in the structure. The characteristic spacing between ring centers matches the length scale of the first sharp diffraction peak (FSDP) in the structure factor, establishing a direct connection between this reciprocal-space signature of MRO and its real-space organization. These results demonstrate that the FSDP, the spatial correlation of the rings, and emergent orientational symmetries are not independent manifestations of MRO, but reflect different aspects of a common structural organization. Our findings provide a unified real-space picture of MRO in amorphous silicon and suggest that intermediate-range structural order in network glasses emerges from the interplay between local bonding constraints and extended atomic arrangements driven by efficient packing.
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All authors Zhen Zhang, Stephen R. Elliott, Yujie Wang, Walter Kob

Disordered Systems and Neural Networks

Seismology of Glasses

Zhiyu Cao and Peter G. Wolynes

Aging and relaxation of glasses proceed through localized rearrangements that also generate long-ranged mechanical responses in their surroundings. We develop a theory that treats these rearrangements as internal microseismic sources, and thereby separates the direct effects emerging from an event from the effects from the far-field displacements it generates. These far-field disturbances propagate and relax through the viscoelastic medium through which they move, producing a stochastic background of weak but numerous perturbations at any given location. Combining the description of local events from the Random First Order Transition theory with this propagating background, we derive a unified equation for the dynamical structure factor of a relaxing glass. The theory identifies a finite wave-vector and time window in which the growing viscoelastic far-field disturbances can produce compressed exponential relaxation, which has been observed using X-ray photon correlation spectroscopy. At higher wave vectors that resolve local jumps, heterogeneity of the local event dynamics instead produces stretched exponential relaxation. The crossover between these behaviors depends on the event statistics and the scattering phase accumulated across the region reached through viscoelastic propagation from the numerous distant sources.
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Soft Condensed Matter

Complex pattern in periodically driven binary Quincke colloids

Chuan Yu Zhang, Mu Yue Zhao, Xiao Yi Zhou et al. (+3 more)

Binary active systems offer a minimal platform for understanding how component heterogeneity organizes non-equilibrium structures. Here we show that in a binary Quincke system driven by a periodic square-wave electric field, a dynamic square lattice in which small particles occupy the lattice-cell centers which are surrounded by large particles emerges spontaneously. Particle-resolved trajectories reveal that the size separation arises from the mobility difference of large particles and small particles. Increasing the driving frequency reduces the single-cycle path lengths of both species and simultaneously decreases the lattice constant. These results show how size-dependent activity,density redistribution, and periodic forcing cooperate to generate tunable complex active patterns.
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All authors Chuan Yu Zhang, Mu Yue Zhao, Xiao Yi Zhou, Wen-De Tian, Kang Chen, Tian Hui Zhang

Materials Science

Magnetic proximity beyond the interface: Layer-sequence-dependent exchange in WSe$_2$/CrI$_3$ heterostructures

Natalie Kuhn, Marc Schütte, Joachim Emming et al. (+8 more)

Magnetic proximity effects in transition metal dichalcogenide (TMD)/2D-magnet heterostructures are often described in terms of the magnetization of the interfacial magnetic layer. Here, we show that this picture is sufficient to describe the neutral-exciton valley splitting of the TMD, but incomplete for its hole-doped electronic structure. We study a gate-tunable van der Waals heterostructure composed of monolayer WSe$_2$ in direct contact with trilayer CrI$_3$. By combining spatially and helicity-resolved reflection-contrast spectroscopy with magnetic circular dichroism, we identify two distinct magnetic domains in the trilayer CrI$_3$: one with purely antiferromagnetic interlayer coupling and one with a mixed antiferromagnetic (AFM)/ferromagnetic~(FM) coupling. In both domains, the sign of the neutral-exciton valley splitting of WSe$_2$ switches with the magnetization reversal of the adjacent CrI$_3$ layer. In contrast, helicity-resolved positive-trion spectroscopy of WSe$_2$ reveals a qualitatively different response. While the AFM domain shows a strongly helicity-selective trion resonance, the mixed AFM/FM domain exhibits trion resonances in both helicities. This behavior disappears when all CrI$_3$ layers are aligned in a parallel magnetization direction. Our results demonstrate that charged excitons are sensitive to the full layer-resolved magnetic sequence of the adjacent 2D-magnet, revealing magnetic proximity beyond the interface.
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All authors Natalie Kuhn, Marc Schütte, Joachim Emming, Felix Hellenkamp, Leo Dreyer, Frank Volmer, Kenji Watanabe, Takashi Taniguchi, Lutz Waldecker, Christoph Stampfer, Bernd Beschoten

Other Condensed Matter · Cross-listed from physics.flu-dyn

Two-Way Coupled Dynamics of Quantized Vortex Bundle Formation in Spatially Periodic Normal-Fluid Turbulence

Hiromichi Kobayashi, Makoto Tsubota and Rio Yokota

Using fully coupled two-way simulations combining the vortex filament model with the Navier–Stokes equations, we discover that quantized vortices in superfluid $^4$He are systematically rolled up into coherent bundles within normal-fluid vortex tubes. Although co-rotating quantized vortices do not aggregate spontaneously, mutual friction with the normal fluid actively drives their bundling, directly inheriting the spatial hierarchy of classical turbulence. Mutual friction excites high-wavenumber normal-fluid vortex tubes adjacent to quantized vortices, while the superfluid forms a nested structure of thick low-wavenumber outer tubes and fine high-wavenumber inner tubes around the vortex lines. A distinct time lag between superfluid kinetic energy and dissipation fuels the energy cascade, giving rise to Kolmogorov's $k^{-5/3}$ spectrum. Crucially, bundle lifetimes are governed by the ratio of the local coupling time scale $t_\mathrm{cl}$ to the Kolmogorov dissipation time scale $\tau_\eta$ ($t_\mathrm{cl}/\tau_\eta < 20$), leading to enhanced thermal stability at higher temperatures. These findings establish a unified mechanism for two-fluid multiscale vortex organization.
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Materials Science

Pressure engineering of the excitonic moiré-potential landscape and exciton-charge interplay in semiconductor moiré superlattices

Wenbing Li, Tianhao Yue, Wenjian Su et al. (+10 more)

Semiconductor moiré superlattices, owing to strongly bound excitons and pronounced electronic correlation, have emerged as an intriguing solid platform for exploring correlated bosonic phenomena, where the moiré potential landscape plays a central role. Hydrostatic pressure allows continuous, in-situ tuning of this landscape, but remains underexplored because of experimental challenges. Here we integrate a diamond anvil pressure cell with high quality dual gated WSe2/WS2 twisted bilayers and perform cryogenic optical spectroscopy. We observe distinct pressure evolutions of moiré intralayer excitons, which reveal drastic modulation of the excitonic moiré-potential landscape captured by a continuum model and suggest the capability of engineering the exciton-band topology. Moreover, we demonstrate efficient pressure control over the interplay between charges and both intralayer and interlayer excitons: the intralayer charge-transfer exciton becomes less sensitive to doping, likely due to reduced charge-transfer character; in contrast, the interlayer exciton exhibits enhanced exciton-charge repulsion. Our results establish hydrostatic pressure as a powerful tuning knob for engineering bosonic quasiparticles and Bose-Fermi interactions in moiré materials.
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All authors Wenbing Li, Tianhao Yue, Wenjian Su, Zhexu Shan, Chen Xu, Jichen Zhou, Kenji Watanabe, Takashi Taniguchi, Liguo Ma, Yuanfeng Xu, Shiyao Zhu, Yang Gao, Yanhao Tang

Disordered Systems and Neural Networks · Cross-listed from q-bio.NC

How Long Is the Coast of a Neuron? Resolution-Dependent Interaction Order and Computational Capacity

Nima Dehghani

Mandlebrot's coastline paradox reframes measurement as a joint property of an object and its ruler. Here we ask how observational resolution shapes the apparent structure of neural computation. We introduce a scale-indexed decomposition that separates the predictive information captured by direct dependencies from the residual outside that model family. Exact constructions show that projection can convert higher-order dependence into pairwise structure. Projection can increase the direct fraction of surviving information even as total predictive information decreases. A schematic branch-to-soma cascade grounds these effects in local coincidence detection, saturating integration and somatic mixing. Resolving organized nonlinear subunits improves approximation and raises effective representational rank. In a nested hierarchy, these gains occur without increasing information about the target. This distinction separates information availability from access by a restricted readout. A point-neuron or direct population model therefore establishes an effective description at a specified scale. It does not uniquely identify the finer computation that generated the observed relation. Which resolution is adequate depends on the observable and perturbation of interest.
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Soft Condensed Matter

Why shaking faster does not untangle: frequency-selective extraction of filaments from tangled matter

Ishant Tiwari, Sutikshan Bansal, Rosalind Huang et al. (+4 more)

Tangles of soft filaments are ubiquitous, from living worm blobs to the cables in a desk drawer. How do such tangles, held together by friction and entanglement, respond when one embedded filament is shaken? We suspend disordered tangles of tunable cohesion and ordered stitched meshes from a single thread (the tether) and oscillate it vertically at fixed amplitude. Extraction peaks at an intermediate drive frequency ($\sim 15$ Hz) and declines at higher frequencies, although the peak drive acceleration grows quadratically. Here we combine experiments, high-speed imaging, and a tension-only spring-mass model to show that this non-monotonic response is set by timing rather than resonance. The extraction window is bounded below by a slackening threshold, where the peak drive acceleration exceeds gravity and the tether, slack for part of each cycle, creates a tensile impulse each time it snaps taut. The window is bounded above by a transmission crossover, where the transmission time across the tangle exceeds a quarter of the drive cycle, so that the tangle no longer responds as a whole and the drive's work dissipates internally. The slackening threshold depends only on the drive and gravity, while the transmission crossover is set only by the tangle's size and transmission speed. By tracing extraction to the overlap of impulse creation and impulse transmission, we identify a generic principle of driven filamentous matter and suggest frequency-selective routes to its disassembly.
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All authors Ishant Tiwari, Sutikshan Bansal, Rosalind Huang, Chenyi Fei, Jörn Dunkel, Vishal Patil, Saad Bhamla

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

Materials Science

ActMOF: Mapping Reticular Synthesis through Active Learning

Hongrui Sheng, Shutian Liang, Reid A. Coyle et al. (+5 more)

Reticular chemistry allows metal-organic frameworks (MOFs) to be designed from their building units, yet their synthesis remains constrained by sparse experimental data, noisy crystallization outcomes, and the absence of benchmarks for comparing active-learning strategies. While data-driven approaches such as Bayesian optimization (BO) can improve synthesis success rates, selecting appropriate optimizers beforehand for mapping MOF crystallization landscapes remains largely empirical. Here we present ActMOF, an experiment-grounded benchmark for comparing search strategies in aluminum-carboxylate MOF synthesis. ActMOF is emulated from experimentally measured microwave syntheses with each encoded condition assigned a crystallinity index calculated based on diffraction peak intensity and full width at half-maximum. By benchmarking policies guided by Gaussian processes (GP), tree ensembles and large language models (LLM), ActMOF placed the GP family among the leading policies for active learning in sparse synthesis landscapes. It then demonstrated transferability by guiding the microwave synthesis of six reticularly related aluminum MOFs. All six campaigns gave crystalline products within a fixed budget of 12 experiments each, and established a reusable testbed for AI-driven MOF synthesis.
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All authors Hongrui Sheng, Shutian Liang, Reid A. Coyle, Shyam Chand Pal, Peter Walther, Bin Feng, Xinyu Ding, Zhiling Zheng

Superconductivity

Phase Stability and Anisotropic Superconductivity in Ternary M2B4C2 (M=Ca, Mg) Monolayer

Jakkapat Seeyangnok, Udomsilp Pinsook and Graeme J Ackland

In this work, we investigate the phase stability, electronic structure, and superconducting properties of the two-dimensional ternary borocarbides MB$_4$C$_2$ (M = Ca, Mg) using first-principles calculations and fully anisotropic Migdal-Eliashberg theory. Ab initio molecular dynamics, phonon dispersion, and elastic constant calculations confirm that both monolayers are dynamically, thermally, and mechanically stable. Electronic structure analysis reveals an intrinsic metallic nature with a multiband Fermi surface, where states near the $\Gamma$ point are dominated by in-plane B-$p_x$, $p_y$ orbitals, while zone-boundary states are primarily derived from out-of-plane B-$p_z$ orbitals. The electron-phonon coupling is determined to be $\lambda = 0.64$ for both materials, driven by the rigid covalent B-B and B-C honeycomb networks. By solving the anisotropic Eliashberg equations, we predict that CaB$_4$C$_2$ and MgB$_4$C$_2$ are nodeless two-gap superconductors with critical temperatures ($T_c$) of 33.4 K and 33.8 K, respectively, at a Coulomb pseudopotential of $\mu = 0.10$. Furthermore, the superconducting state remains robust under increased Coulomb repulsion ($\mu = 0.13$), retaining elevated $T_c$ values of 31.2 K and 30.9 K, respectively. These findings establish MB$_4$C$_2$ monolayers as promising candidates for nanoscale superconducting applications and enrich the family of two-dimensional multigap superconductors.
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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

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

The noise cost of reservoir locality in broadband quantum amplifier chains

Chengxi Li, Hao Zhu, Tie-Fu Zhang et al. (+3 more)

Directional quantum amplifiers enable weak-signal readout while protecting the source, but reservoir noise limits sensitivity. Finite-band suppression must reconcile frequency-dependent responses with fixed local couplings and finite rates. We construct adjacent-site loss channels attaining the known single-frequency minimum under local compatibility conditions, as an uncapped benchmark. For specified uniform and dimerized chains, we compare fixed reservoirs at matched drift, ports, high-gain band and complete gain/loss rate caps. At the representative cap $R=8$ and halfwidth $\Omega=0.05$, nearest-neighbor arithmetic band average noise exceeds the unrestricted optimum by more than $1.01265$ quanta in the uniform chain for every finite $N\ge64$. Boundary-response bounds give necessary rates and targets requiring range two. At $N=64$, finite-auxiliary calculations retain a noise advantage under matched total coupling budgets; response bounds quantify noise-resolution tolerances. These theoretical results guide reservoir design and noise calibration for a proposed cryogenic microwave array with a $100$ kHz design band.
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All authors Chengxi Li, Hao Zhu, Tie-Fu Zhang, Lin Zhuang, Wanzi Sun, Wuming Liu

Statistical Mechanics · Cross-listed from hep-th

Mutual Information of Measurement in Conformal Field Theories

Israel Klich, Ravisankar Rajagopal and Diana Vaman

The mutual information of measurement of a local operator between two spatial regions characterizes the reduction in the uncertainty of measurement outcomes in one region given the outcome in the other. We study the Rényi-Shannon mutual information of measurement in conformal field theories (CFTs). Explicit calculations for scalar primaries and descendants in large $N$ CFTs are performed in the two extreme limits of the intervals being adjacent or largely separated. The results depend on only the cross ratio and the scaling dimension $\Delta$ of the operator being measured, with striking similarities to the mutual information of entanglement. We find a surprising quadratic dependence as $(\Delta-1/2)^2$ for adjacent intervals. This dependence superficially seems to violate the information processing inequality, which we discuss and resolve. We also offer a holographic interpretation of the mutual information of measurement.
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Mesoscale and Nanoscale Physics

Chern insulator optics

Jason G. Kattan and J. E. Sipe

Chern insulators have optical properties that are strikingly different than ordinary chiral media. Unlike the natural optical activity of the latter, which is a finite-wavelength effect arising from spatial dispersion, the optical activity of a Chern insulator is already present in the long-wavelength limit, and exhibits a striking directional asymmetry in the propagation of circularly polarized light. We study this unnatural optical activity using a recently developed field theory for Chern insulators. For bulk Chern insulators, we derive the normal-incidence transmission and reflection coefficients of multilayer structures, identify the associated Faraday and Kerr angles, and show that these optical rotations provide a direct optical signature of topology at low frequencies. We also show that an interface between bulk Chern insulators can act as a kind of mirror, completely reflecting light at normal incidence when the Chern invariants have opposite signs. Moving to a more realistic model of a two-dimensional current sheet, we study the Faraday and Kerr effects in a thin film of $\mathrm{Mn}\mathrm{Bi}_2\mathrm{Te}_4$ in its Chern insulator phase. The predicted rotations are many orders of magnitude larger than those of optically active media of comparable thickness that are topologically trivial.
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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

Materials Science

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

Statistical Mechanics

Beyond the lemon: Spectra of random Lindblad operators with a Hamiltonian component

Mykhailo Hontarenko, Wojciech Tarnowski, Sergey Denisov et al. (+1 more)

Generators of continuous-time quantum Markovian evolution, known as Lindblad operators, play a key role in the theory of open quantum systems. The question of how to define and characterize random Lindblad operators has attracted considerable attention in recent years. Purely dissipative random Lindbladians have been extensively studied using toolboxes of free probability and non-Hermitian random matrix theories, which helped, among other results, to uncover a characteristic lemon-like spectral support. In this work, we focus on random Lindbladians with a Hamiltonian component. We analyze three ensembles of increasing complexity, designed to illustrate the joint effects of dissipative and Hamiltonian dynamics. While the first two ensembles allow for an exact analytic treatment with standard probabilistic and free-probability methods, the generic case of independently random Hamiltonian and dissipative components requires a novel framework that combines operator-valued free probability with sequential noise averaging. For this ensemble, our approach preserves the underlying tensor-product structure of the Lindblad operator and derives a general equation for the spectral boundary. We characterize the effect of Hamiltonian-induced spectral squeezing and explain how the spectral support changes with the relative Hamiltonian strength and the rank of the dissipative component.
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All authors Mykhailo Hontarenko, Wojciech Tarnowski, Sergey Denisov, Karol Życzkowski

Materials Science · Cross-listed from math-ph

On the Mathematical Structure of Helical Shear in Anelastic Continua

Souhayl Sadik, Giuseppe Saccomandi and Luigi Vergori

We study helical shear of a thick-walled tube made of an incompressible, isotropic hyper-anelastic solid carrying a radially symmetric distribution of axial screw dislocations. Through the Bilby–Kröner–Lee decomposition, the dislocations are encoded in a Weitzenböck material manifold, whose Riemannian metric alone enters the elastic response. Equilibrium reduces at each radius to an algebraic system for the azimuthal and axial shear strains, whose cross terms are proportional to the dislocation strength and to the dependence of the strain energy on the second invariant; the two shear modes therefore couple only in the presence of dislocations. Exact solutions are obtained for neo-Hookean, Fung–Demiray, Gent, Knowles, and Mooney–Rivlin materials, and numerical ones for Gent–Gent materials. The universal relations of Horgan and Saccomandi are extended to dislocated generalized neo-Hookean tubes. Dislocations stiffen the tube when the strain energy stiffens with the first invariant, couple the two shear modes chirally when it depends on the second, and may restrict admissibility: they cap the dislocation strength in Gent and Gent–Gent materials, and contract the admissible traction region in Knowles materials with power-law index below n = 1/2. A weakly nonlinear analysis to third order in the applied tractions and dislocation strength shows that, at first order (linear elasticity), the dislocations leave the shear response unaffected while carrying a residual stress. The chiral coupling enters at second order, through the dependence of the strain energy on the second invariant, so that every dislocated material couples the modes as the Mooney–Rivlin solid with the same second- and third-order moduli. At third order, no new coupling arises; the modes interact through stiffness corrections involving the fourth-order modulus, which the dislocations further correct mode by mode.
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Quantum Gases · Cross-listed from quant-ph

Selective Control and Imaging of Higgs and Goldstone Modes with a Quantum Simulator

Connie Miao, Pranjal Praneel, Thomas G. Kiely et al. (+5 more)

We realize the mesoscopic Bose-Hubbard model at unit-filling on a two-dimensional array of transmon qubits and selectively excite collective modes associated with amplitude or phase fluctuations of the superfluid order parameter. We identify these modes respectively as the Higgs and Goldstone modes using complementary local observables, extracted from measuring the number of particles on each site. Modulation of the coupling between sites excites the Higgs mode, which we detect via the density of doubly occupied sites. In contrast, modulation of the local chemical potential with an appropriately chosen spatial profile excites the lowest-frequency Goldstone mode, which we detect via changes in the local density. The two modes have different symmetries and do not couple to one another. By varying the system geometry, we characterize the impact of finite system size on the evolution of both modes. In the thermodynamic limit, decay into a continuum of lower-energy excitations can obscure the Higgs response. In our mesoscopic system, however, the finite system size leads to spectral gaps and allows us to detect the Higgs mode as a coherent, long-lived excitation. Our work demonstrates how finite quantum simulators can isolate and probe physical phenomena that become difficult to resolve in the thermodynamic, large-scale limit.
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All authors Connie Miao, Pranjal Praneel, Thomas G. Kiely, Eliott Rosenberg, Nicole S. Ticea, Pedram Roushan, Erich Mueller, Andre G. Petukhov

Mesoscale and Nanoscale Physics · Cross-listed from math-ph

On optimal Wannier decay in dimension three

Simon Becker, Zhongkai Tao and Mengxuan Yang

For a Chern nontrivial Bloch bundle over the three torus, we construct an orthonormal Wannier basis with the optimal pointwise decay $\mathcal{O}(|x|^{-5/2})$. All but one of the generators decay exponentially. This resolves the question left open in arXiv:2505.01999.

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Cavity-assisted dynamic nuclear polarisation

Tristan Lorriaux, Yutian Wen, Patrice Bertet et al. (+2 more)

Dynamic nuclear polarisation transfers polarisation from electron to nuclear spins by relying on a dissipative channel. Here we introduce a cavity-based DNP mechanism which uses the radiative relaxation of the electronic spin through the Purcell effect to bring about the nuclear spin polarisation. We implement this protocol on an ensemble of bismuth donor spins (I=9/2, S=1/2) in isotopically purified silicon coupled to a superconducting resonator. A single cycle, combining adiabatic microwave and radio-frequency pulses with Purcell relaxation, increases a target ground state's population by a factor of $1.79\pm0.04$; a cumulative enhancement of $4.6\pm0.2$ is reached with additional cycles, to be compared with the theoretical limit of ninefold set by the degeneracy of the ground manifold. We explain this difference by the competition between Purcell and intrinsic relaxation on the one hand and a collective effect that slows down the electronic spin radiative decay as the nuclear spin population grows on the other hand. Our results place radiative DNP as an available mechanism at millikelvin temperatures where phonon-mediated relaxation is frozen.
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All authors Tristan Lorriaux, Yutian Wen, Patrice Bertet, Benjamin Huard, Audrey Bienfait

Materials Science

Symmetry-selected extreme shear compliance in a stable carbon monolayer

J. W. González, M. Pachecho and J. D. Correa

Solids that are stiff to most loads and extremely compliant to one are normally built, not found. That internal atomic relaxation lowers elastic constants is textbook; what has remained untested is whether it can be driven far enough to separate the elastic scales of a crystal by an order of magnitude while leaving it mechanically stable. Density functional theory calculations of the complete in-plane elastic tensor of four non-hexagonal carbon monolayers sharing a square lattice metric show that it can: their longitudinal stiffnesses agree to within a factor of two while their shear constants span more than a factor of fifty. Twin T-graphene, previously reported as elastically isotropic from normal strains alone, is the extreme case, with $C_{66}=3.03$~N\,m$^{-1}$, nearly fifty times below graphene, at an axial stiffness typical of semiconducting monolayers, and a soft Kelvin eigenvalue a factor of $29$ below the others while the Born criteria hold. Symmetry confines the strain-induced relaxation to the $B_{2g}$ sector, a counter-torsion of the carbon sublayers about the short mid-plane bonds that removes $96\%$ of the clamped-ion shear stiffness with almost no bond stretching and leaves the semiconducting gap intact. Transverse acoustic phonons, finite-temperature dynamics, and large-deformation simulations show that the channel survives beyond the harmonic, zero-temperature limit. Because the selection rule is a point-group statement rather than a chemical one, it yields a screening criterion for other crystals and other strain components.
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Mesoscale and Nanoscale Physics

Pseudo-relativistic fermions and topological states in zinc-blende semiconductors and their heterostructures (Habilitation thesis)

Sergey S. Krishtopenko

Tracing my scientific path from many-body physics in semiconductor nanostructures to topological quantum matter, this Habilitation à diriger des recherches (HDR) memoir presents only part of my research since defending two PhD theses in Toulouse and Nizhny Novgorod in 2011. Focusing on pseudo-relativistic fermions and topological states in zinc-blende semiconductors and their heterostructures, it highlights my independent research program: identifying physical problems, developing predictive theories, and initiating new directions with experimentalists. The first part addresses Kane fermions in bulk HgCdTe: temperature-driven band inversion, domain-wall states, the collapse of Landau levels in crossed electric and magnetic fields, and disorder-induced topological transitions. The second examines pressure-, temperature-, and disorder-driven phase transitions in single and double HgTe quantum wells (QWs), including bilayer-graphene-like semimetals and a two-dimensional higher-order topological insulator (2D HOTI) phase beyond the minimal BHZ model. The third develops three-layer InAs/Ga(In)Sb QWs as a III-V platform for massless Dirac fermions, large-gap quantum spin Hall insulators, 2D HOTI phases, and semimetals with quadratic band touching, and discusses InAs$_{x}$Sb$_{1-x}$/InAs$_{y}$Sb$_{1-y}$ heterostructures as a promising alternative. Several of these predictions are supported by experimental observations, including quantized helical edge transport up to 60 K and the unconventional quantum Hall effect. Defended on March 25, 2026, at the University of Montpellier. Jury: Michel GOIRAN (chair and rapporteur, LNCMI-CNRS, Toulouse); Alexey KAVOKIN (rapporteur, Westlake University, Hangzhou); Robson FERREIRA (rapporteur, LPENS-CNRS, Paris); Alexei BARANOV (member, IES-CNRS, Montpellier); Benoit JOUAULT and Frédéric TEPPE (members, L2C-CNRS, Montpellier).
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Statistical Mechanics · 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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Materials Science

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