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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 24 June

Soft Condensed Matter

Mechanical response of quasi-two-dimensional colloidal clusters under uniaxial tension

Yanhui Yang, Jiawei Kang, Yao Li et al. (+1 more)

Despite extensive studies of equilibrium conformations of colloidal clusters, little is known about their mechanical response. Here, we investigate the tensile behavior of a quasi-two-dimensional colloidal cluster subjected to uniaxial tension up to fracture. The sample is a ribbon-shaped assembly of 16 colloidal beads bound by short-range depletion attraction. Using multiple optical tweezers, we clamp the cluster at both ends and perform a tensile test along its long axis. Combining video microscopy with particle tracking, we measure the tensile stress, strain, and particle configurations during deformation. We observe diverse mechanical response behaviors, including elastic, plastic, and soft-mode deformation, with fracture occurring at a strain near 10%. To explain these behaviors, we construct a spring-mass frame model with breakable elastic bonds. We perform canonical Monte Carlo simulations on the full model with 32 degrees of freedom and compute the statistical distributions of mechanical observables using a simplified model with only 7 degrees of freedom. Both the simulations and the theoretical calculations accurately reproduce the experimental stress–strain curves. Moreover, the configuration distributions predicted by the simplified model agree well with both experiment and simulation in the elastic and soft-mode regimes, with only minor discrepancies in the plastic regime. This work demonstrates that the simplified spring-mass model captures the essential physics governing the rich tensile response behavior of the colloidal cluster.
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All authors Yanhui Yang, Jiawei Kang, Yao Li, Xiaoguang Ma

Disordered Systems and Neural Networks · Cross-listed from quant-ph

Two-dimensional Hyperbolic RNN Neural Quantum State

H. L. Dao

In the first part of this work, we construct the first type of two-dimensional (2D) hyperbolic neural quantum state (NQS) in the form of the Lorentz 2DRNN (Recurrent Neural Network) and benchmark its performance against the Euclidean 2DRNN in the paradigmatic $N \times N$ 2D Transverse Field Ising Model (2DTFIM) setting with different lattice sizes up to N = 12 at different transverse magnetic field strengths. We find that hyperbolic Lorentz 2DRNN NQS robustly outperforms Euclidean 2DRNN NQS in our experiments when the system is at the phase transition point, where the physics can be described by a conformal field theory (CFT) - known via the AdS/CFT holographic duality to possess an underlying hyperbolic geometry. In the second part of this work, we benchmark the performances of recently introduced one-dimensional (1D) hyperbolic NQS ansatzes (including Poincare RNN/GRU and Lorentz RNN/GRU) against their Euclidean versions in $N \times N$ 2DTFIM, converted to a one-dimensional sequence. The findings extend our previous results showing that 1D hyperbolic NQS robustly outperforms 1D Euclidean NQS, thanks to the combined effects of the induced 1st and Nth neighbor interaction hierarchy and the CFT physics at criticality. While studies on larger system sizes remain future work, this study serves as a proof-of-concept for the utility, effectiveness, and superior performance of 1D and 2D hyperbolic NQS ansatzes compared to conventional Euclidean NQS models in many-body quantum systems - particularly those exhibiting structural hierarchy, criticality, or a combination of both.
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Materials Science

A topology-tuned pressure valve across the isoreticular RHO zeolite family

Salvador R. G. Balestra, Antonio Rivas-Blanco, Said Hamad et al. (+1 more)

The isoreticular index of the eight-member embedded RHO zeolite hierarchy operates as a phenomenological design knob that tunes the mechanical critical pressure of the framework valve from $\sim 0.94$ GPa for parent RHO down to a predicted $\lesssim 0.03$ GPa for the largest member PST-28, more than an order of magnitude lower across a single family of synthesizable nanoporous solids. The molecular-valve effect that defines zeolite RHO (a reversible centric-to-acentric phase transition triggered by water, gas pressure, or mechanical loading) is shown here to be not a peculiarity of the smallest member but a generic property of the whole hierarchy, with a critical pressure that decays exponentially with the isoreticular order $k$. Combining lattice dynamics, full elastic-constant tensors, and finite-temperature free-energy reconstructions within a classical core-shell description of the pure-silica frameworks (independently validated against r$^2$SCAN+rVV10 density-functional theory on $G_1$ and $G_2$), we find that the entire family is well described by an effective mean-field Landau picture in which the framework distortion couples quadratically to the volumetric strain. We emphasise that $p_c$ is a mechanical (hydrostatic) critical pressure of the bare pure-silica framework, used as a proxy for the intrinsic framework softness and for the cation- and dehydration-driven response of the real aluminosilicates; it is not a gas-adsorption pressure. The exponential extrapolation places $p_c(G_6\text{-}G_8) \lesssim 0.1$ GPa (model-dependent band $0.03$-$0.15$ GPa), identifying the higher-order members as the softest, most stimuli-responsive frameworks of the hierarchy; whether this intrinsic softness translates into guest-driven switching at low gas activities will depend on the Al distribution, extra-framework cations and adsorbed molecules, and remains to be tested experimentally.
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All authors Salvador R. G. Balestra, Antonio Rivas-Blanco, Said Hamad, A. Rabdel Ruiz-Salvador

Soft Condensed Matter

Mode-locking in a colloidal ring driven by power-modulated optical tweezers

Muyang Huang, Pik-Yin Lai and Xiaoguang Ma

Particles and clusters moving across real-space periodic potentials can become locked to discrete directions or orientations due to competing symmetries. Here, we demonstrate an analogous locking phenomenon within a synthetic frequency space. We drive ring-shaped colloidal clusters using a circular optical tweezer array, where power modulation of the traps generates coexisting, distinct potential waves. Relative displacements between the cluster and these waves trace zigzag trajectories across a synthetic two-dimensional lattice, mirroring directionally locked motion in real-space periodic potentials. By tuning the relative wave amplitudes, both the cluster's direction in synthetic space and its velocity in real space exhibit discrete plateaus, both governed by square-lattice symmetry. Furthermore, the formation of superlattices between the particles and potential wave minima mirrors the characteristic features of kinetically locked two-dimensional clusters, demonstrating the capability to explore driven cluster dynamics within higher-dimensional potentials using lower-dimensional setups. Our findings establish new strategies for controlling transport of particle clusters via power-modulated laser tweezers.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Preparing two-mode magnonic Schrödinger cat states in a cavity-magnon-qubit system

Gen Li, Gang Liu, Rong-Can Yang et al. (+1 more)

The cavity-magnon-qubit system has recently been demonstrated as a new platform for preparing macroscopic quantum states in magnonic systems. Here, we propose to prepare a two-mode magnonic cat state, which is also a non-Gaussian entangled state, based on this practical system involving two yttrium-iron-garnet (YIG) spheres and a superconducting qubit coupled to a common microwave cavity. By adiabatically eliminating the cavity and resonantly driving the qubit, an effective magnon-qubit conditional-displacement interaction is achieved. Further working in the magnon-magnon strong-coupling regime and considering two identical magnon frequencies and coupling strengths to the cavity, two hybridized magnon modes are formed, of which the bright mode is prepared in a cat state after a projective measurement on the qubit, while the dark mode remains in its initial vacuum state. Such a state corresponds to a two-mode cat state of two original magnon modes, which share strong non-Gaussian entanglement. We also discuss practical dissipation and dephasing effects on the cat state. The results indicate that strong nonclassicality and non-Gaussian entanglement are present in the two-mode cat state using fully feasible parameters.
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All authors Gen Li, Gang Liu, Rong-Can Yang, Jie Li

Statistical Mechanics

Dynamic dissipative structures in bistable magnetic ordered spin crossover systems: self-oscillations of magnetization

Yu.S. Orlov, N.N. Paklin, S.V. Nikolaev et al. (+2 more)

Dissipative systems can exhibit a variety of behavioral modes, ranging from complex deterministic chaos to the spontaneous emergence of ordered structures. A simple example of the latter is Benard cells. More complex examples include lasers, droplet clusters, the Belousov–Zhabotinsky reaction, and biological life. Of particular interest in the context of the formation of spatiotemporal dissipative structures are bistable systems with spin crossover. This paper discusses the possibility of observing self-oscillations of magnetization in magnetically ordered systems with spin crossover. The results of theoretical calculations of the nonlinear dynamics of bistable magnetic systems under nonequilibrium conditions are presented.
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All authors Yu.S. Orlov, N.N. Paklin, S.V. Nikolaev, E.I. Shneyder, V.A. Dudnikov

Materials Science

A Differentiable DFT-Based Framework for Inverse Materials Design

Kohei Ishii, Hisazumi Akai, Tetsuya Fukushima et al. (+2 more)

Discovering solid-state materials with target properties remains a central challenge in computational materials science. Existing approaches – high-throughput screening, surrogate optimization, and generative models – require extensive evaluations or training data and extrapolate poorly to unseen compositions. Here we develop a first-principles inverse-design framework, integrating reverse-mode automatic differentiation (AD) into KKR-CPA – the Korringa–Kohn–Rostoker method with the coherent potential approximation – where atomic compositions are continuous variables to be optimized. Reverse-mode AD yields gradients of objective functions with respect to composition at a cost independent of the number of candidate elements, enabling gradient-based optimization to identify materials from compositional spaces spanning dozens of elements. In this framework, any computable quantity can serve as the objective. We demonstrate this generality through two contrasting applications, magnetic alloys and half-metals, yielding candidates such as (Lu$_{0.553}$Yb$_{0.447}$)(Co$_{0.759}$Fe$_{0.241}$)$_2$Fe$_3$ and FeZr(Sb$_{0.94}$Te$_{0.06}$). Our framework offers a physically grounded route from a target property to the material that realizes it.
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All authors Kohei Ishii, Hisazumi Akai, Tetsuya Fukushima, Hikari Shinya, Koji Inui

Strongly Correlated Electrons

Automatic-differentiation-enabled dynamic parameter retrieval with sub-pulse-width resolution

Huaiyue Peng, Yuchen Lin, Fu Deng et al. (+2 more)

Time-resolved terahertz time-domain spectroscopy (THz-TDS) is a phase-sensitive tool in condensed matter physics for tracking photoinduced non-equilibrium dynamics of low-energy elementary excitations. However, the measured response function, optical conductivity $\sigma(\omega,t_{pp})$, becomes unreliable in reporting the state of matter when material properties drastically change on a timescale comparable to or less than the probe pulse duration, obscuring the sub-pulse-width dynamics. To resolve this issue, we present a full-waveform inversion framework inspired by the multi-dimensional retrieval philosophy of frequency-resolved optical gating (FROG). By leveraging the automatic differentiation (AD) technique and the two-dimensional time-domain signal $E(t_{g},t_{pp})$, we show one can uniquely solve the inverse problem, at the sub-pulse-width resolution, of retrieving physical observables that are still well-defined, i.e., time-dependent scattering rate $\gamma(t)$, plasma frequency $\omega_\mathrm{p}(t)$ and resonance frequency $\omega_0(t)$, while the response functions are not. Further optimization by gradient-based routines (Adam + L-BFGS) via JAX makes the method exceptionally robust against experimental noise and probe pulse distortions. The validity of the AD-enabled methodology is benchmarked both by a self-consistent numerical approach and by experimental data from real ultrafast THz spectroscopy measurements.
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All authors Huaiyue Peng, Yuchen Lin, Fu Deng, Xiaoyue Zhou, Jingdi Zhang

Materials Science

Spin-flip optical excitations in van der Waals antiferromagnet CrPS$_4$

Dipankar Jana, Aljoscha Soll, Zdenek Sofer et al. (+4 more)

We investigate the near-infrared optical response of the semiconducting van der Waals antiferromagnet CrPS$_4$ and identify previously unreported spin-entangled optical resonances. The strong and anisotropic magnetic-field dependence of these resonances reflects the underlying magnetic order and confirms the biaxial antiferromagnetic nature of CrPS$_4$. From the magnetic field evolution of the optical transition, we extract key magnetic parameters, including the spin-flop ($\approx0.9$~T) and spin-saturation ($\approx8$~T) fields. These results demonstrate a potential pathway for all-optical probing of spin states in van der Waals antiferromagnets, with relevance for spin-sensitive optoelectronic and magneto-optical devices.
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All authors Dipankar Jana, Aljoscha Soll, Zdenek Sofer, Milan Orlita, Clement Faugeras, Maciej Koperski, Marek Potemski

Soft Condensed Matter

Suppression of Active Super-Diffusion: Impact of String Defects and Canted Multi-Domains

Ritik Rajak, Manish Agarwal, Sanjay Puri et al. (+1 more)

We investigate the transport dynamics of an active Brownian particle (ABP) traversing a complex, non-Newtonian liquid crystal (LC) matrix. Employing the Generalized Lebwohl-Lasher (GLL) model, we systematically vary higher-order orientational interactions to stabilize three distinct host environments: isotropic, uniform nematic, and structurally frustrated canted phases. Modeling the coupled system via off-lattice over-damped Langevin dynamics, the resulting trajectories are characterized by evaluating their step-size distributions (SSDs), mean-square displacements (MSDs), and Hurst exponents. In the uniform nematic phase, the anisotropic matrix elastically channels the ABP, producing a left-skewed exponential SSD and persistent ballistic motion parallel to the director $\hat{\mathbf{n}}$. Similarly, transverse transport obeys a Rayleigh distribution and acquires a prominent $t \ln t$ super-diffusive correction-an explicit signature of the particle coupling to the host's gapless transverse Goldstone modes, as predicted by Toner et al. [Phys. Rev. E 93, 062610 (2016)]. Crucially, we reveal that this active super-diffusion is systematically suppressed when the long-range Goldstone fluctuations are disrupted by topological defects. This breakdown manifests both macroscopically within the fractured, multi-domain canted phase due to a structural mass gap, and locally in the unfrustrated nematic phase through scattering by vortex disclination lines. Consequently, while the local SSDs qualitatively mirror the ideal nematic state, the transverse $t \ln t$ scaling vanishes in the presence of these structural constraints. Our findings demonstrate that tuning the background defect architecture of a complex fluid can fundamentally alter the transport universality class of active matter, offering a novel paradigm for controlling microscopic mobility.
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All authors Ritik Rajak, Manish Agarwal, Sanjay Puri, Varsha Banerjee

Superconductivity

Emergence of Quasi-two-dimensional Superconductivity in W-doped Bulk Noncentrosymmetric 3$R$-TaSe$_2$

P. Manna and R. P. Singh

Noncentrosymmetric transition-metal dichalcogenides offer a rich environment for the study of unconventional superconducting phenomena. Here, we present a comprehensive analysis of single-crystalline W-doped 3$R$-TaSe$_2$, revealing weakly coupled anisotropic unconventional superconductivity at $T_c$ = 2.82(2) K, with an in-plane upper critical field exceeding the Pauli limit by 1.7 times. The angular dependence of the upper critical field, along with the observation of a Berezinskii-Kosterlitz-Thouless transition, reveals quasi-two-dimensional superconductivity. Crucially, magnetotransport reveals a distinct two-fold rotational symmetry within the superconducting state under in-plane fields, breaking the underlying three-fold lattice symmetry. These findings establish W-doped $3R\text{-TaSe}_2$ as a bulk model system for exploring intrinsic low-dimensional superconductivity and broken rotational symmetry, thus opening new directions for future quantum technologies.
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Strongly Correlated Electrons

Spin-imbalanced fermion on a dynamic lattice

Jie Liu, Xiaofan Zhou and Suotang Jia

We investigate the magnetic order of a one-dimensional spin-1/2 fermion dynamical lattice, where itinerant fermions are coupled to bond-centered localized spins via an Ising-like spin dependent hopping. The model provides an anisotropic dynamical extension of conventional spin-1/2 fermion systems, in which the motion of itinerant fermions is directly modulated by the configuration of localized spins. Using density matrix renormalization group simulations, we map out the ground state phase diagram in various parameter spaces. Depending on the interplay among the hopping dependent on localized spins, the longitudinal field, and the external Zeeman field, two distinct phases are obtained: a paramagnetic phase and a spin-density-wave phase. Most notably, in the partially spin-polarized fermion phase, the spin-density wave ordering wave vector exhibits two distinct phenomena, corresponding respectively to the nesting vectors $2k_{F\uparrow}$ and $2k_{F\downarrow}$ of the spin-resolved Fermi surfaces. We further demonstrate that the two spin-density wave phases are robust against the repulsive Hubbard interaction between itinerant fermions. Our results reveal a novel route for tuning magnetic modulations in one-dimensional correlated systems and enrich the microscopic understanding of dynamical lattice magnetism.
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Materials Science

Intrinsic Defect Energetics and Fluorine Doping Effects in Li2CO3 and Li2O2: A First-Principles Study

Youjeong Choi, Tasuku Sugiura, Keisuke Mukai et al. (+3 more)

Lithium carbonate, Li2CO3, is a thermodynamically stable carbonate phase whose defect energetics are closely related to its stability and decomposition behavior in various lithium-based electrochemical systems. These properties of Li2CO3 are particularly important in lithium-oxygen battery environments. In these systems, Li2CO3 can form as a parasitic discharge product alongside Li2O2, the primary discharge product, leading to performance degradation. However, compared with Li2O2, the intrinsic defect thermodynamics of Li2CO3 and how chemical doping modifies its defect energetics remain insufficiently understood. In this study, first-principles calculations were performed to systematically analyze the intrinsic point-defect energetics of Li2CO3 and to evaluate the effects of fluorine doping on vacancy formation energies in Li2CO3 and Li2O2. Intrinsic defect analysis reveals that defect behavior is predominantly governed by lithium-related defects. Upon fluorine doping, lithium and carbon vacancy formation energies decrease selectively in Li2CO3, partially destabilizing the carbonate framework, while a reduction in lithium vacancy formation energy is also observed in Li2O2. These results suggest that fluorine doping modulates the defect energetics of both discharge products, potentially providing a thermodynamic basis for controlling the stability of Li2CO3 and Li2O2 under thermodynamic conditions representative of lithium-oxygen batteries.
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All authors Youjeong Choi, Tasuku Sugiura, Keisuke Mukai, Nanako Ishihara, Shuji Nakanishi, Teruyasu Mizoguchi

Strongly Correlated Electrons

Spectroscopic signatures of Kohn anomaly in a topological crystalline insulator

Jingwen Li, Arpita Dutta, Kush Saha et al. (+4 more)

Topological crystalline insulators extend the concept of topological insulators by hosting surface states protected by crystallographic symmetry. Their topological phase transitions arise from spin-orbit-driven band inversion in the bulk electronic structure, reshaping the low-energy electronic environment and its coupling to lattice excitations. While the electronic aspects of band topology are well established, the corresponding dynamics of lattice and electron-phonon interactions remain largely unexplored. Here, we report a pronounced softening of a low-energy surface phonon mode across the topological phase transition in Pb$_{0.77}$Sn$_{0.23}$Se, revealed by temperature-dependent time-domain terahertz spectroscopy. Unlike the well-known phonon softening in ferroelectrics, this effect does not signal a structural instability but instead reflects electronic reconstruction. We attribute the softening to the spectroscopic manifestations of a Kohn anomaly, indicating a strong coupling between lattice vibrations and Dirac-like surface electrons in the topological phase. Consistently, the phonon linewidth deviates from the standard anharmonic temperature dependence, further evidencing enhanced electron-phonon coupling. The observed changes in phonon frequency and linewidth at around 120 K are consistent with the reported topological phase transition temperature in this material. Our results thus provide a spectroscopic route for the distinct identification of the onset of a topological phase.
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All authors Jingwen Li, Arpita Dutta, Kush Saha, Andrzej Szczerbakow, Tomasz Story, Manfred Fiebig, Shovon Pal

Materials Science · Cross-listed from physics.app-ph

Wide-field NV magnetometry under simultaneous high-pressure and high-temperature conditions

Masahiro Ohkuma, Eikichi Kimura, Shumpei Ohyama et al. (+7 more)

We demonstrate wide-field optically detected magnetic resonance (ODMR) under simultaneous high-pressure and high-temperature conditions using nitrogen-vacancy (NV) centers. Although NV-center magnetometry has been widely used for spatially resolved magnetic-field imaging, its application to extreme environments combining pressure and temperature remains challenging. In this work, we show that ODMR can be observed at 5 GPa and 500 K, demonstrating the feasibility of NV spin readout under such combined extreme conditions. We further perform wide-field ODMR of iron at 7 GPa and 500 K, where the stray magnetic field from the sample is spatially visualized through the pressure cell. These results establish NV-center magnetometry as a promising platform for imaging magnetic phenomena in materials under high-pressure and high-temperature environments.
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All authors Masahiro Ohkuma, Eikichi Kimura, Shumpei Ohyama, Miu Tezuka, Ryo Matsumoto, Shinobu Onoda, Yoshihiko Takano, Shintaro Azuma, Kenji Ohta, Keigo Arai

Quantum Gases

A Unified Josephson Dynamics Perspective for Single-Cavity BECs: From Self-Trapping to Dynamical Phase Transitions

Soi-Chan Lei

We investigate a two-component Bose-Einstein condensate (BEC) strongly coupled to a single optical cavity, effectively described by a mean-field Dicke model supplemented with interatomic nonlinearities. Here, we propose a unified theoretical framework demonstrating that macroscopic quantum self-trapping (MQST) natively emerges between two internal atomic energy levels within a single cavity. By deriving the dimensionless semiclassical Josephson equations (SJE) governing this purely internal-state architecture, we analytically determine the critical nonlinear threshold and intrinsic phase shift mechanism for the phase transition. Based on this framework, we present two approaches for manipulating quantum phase transitions: dynamic in-situ tuning via photon pumping and inducing non-equilibrium dynamical phase transitions (DPT) via real-time parameter quenches. Furthermore, we rigorously prove that the effective charging energy driving this system scales exactly as one-quarter of the effective spin-dependent interaction energy – the precise parameter governing recent spin-orbit coupled (SOC) BEC experiments. Incorporating realistic $^{87}$Rb atomic parameters, we substantiate that these single-cavity MQST and transition dynamics are highly feasible for observation under current state-of-the-art cold-atom technologies.
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Quantum Gases

Kosterlitz–Thouless Criticality in a Dipole-Conserving XY Model

Han-Xie Wang, Shuai A. Chen, Zheng Yan et al. (+1 more)

In this Letter, we study finite-temperature phase transitions in a two-dimensional classical statistical model called “dipole-conserving XY model”. Unlike the conventional XY model, the original phase field $\theta$ has no quasi-long-range order, conventional phase vortices have finite self-energy, and the standard helicity modulus vanishes identically. Analytic vortex energetics and Gaussian continuum theory show that Kosterlitz–Thouless (KT) criticality is instead controlled by phase-gradient (PG) vortices defined in the two compact dipole fields $\chi_\alpha=a\partial_\alpha\theta$, whose self-energies grow logarithmically with system size. We determine the phase diagram using parallel-tempering Metropolis Monte Carlo simulations and three diagnostics tailored to dipole conservation. KT finite-size scaling of dipole-field correlation-ratio crossings locates the critical temperatures; generalized helicity moduli defined through quadratic phase twists measure the stiffness of individual dipole channels; and PG-vortex densities obtained from plaquette winding numbers identify the proliferating vortex species. At isotropic couplings, the two PG-vortex species unbind simultaneously at a single KT transition. Spatial anisotropy separates their unbinding temperatures, yielding two KT transitions and an intermediate phase with quasi-long-range order in only one dipole channel. The transitions merge again when the mixed-derivative channel is removed. Our results establish the finite-temperature phase structure of the dipole-conserving XY model and identify thermal PG-vortex unbinding as a novel route to KT criticality in systems with higher-moment conservation.
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All authors Han-Xie Wang, Shuai A. Chen, Zheng Yan, Peng Ye

Superconductivity

Universal behavior of the condensation energy of Superconducting BCS Bose gases

Juan José Valencia Acevedo, Miguel Ángel Solís Atala, Patricia Salas Casales et al. (+1 more)

Using the Boson-Fermion formalism of superconductivity we calculate the condensation energy for several superconductors ranging from conventional to unconventional, or high temperature superconductors. It is calculated as the difference between the Helmholtz free energies of the superconducting and the normal state, which is a gas of N attractive electron gas, while the superconducting state is formed by the condensed Cooper pairs taken as composite bosons, coming from a fraction of the electrons inside the Debye shell, plus those electrons inside and outside the Debye shell that are unable to pair. After giving the analytic expressions for the internal energy U and the entropy S we obtain the Helmholtz free energy F = U -TS for both the superconducting and the normal states as functions of temperature. In the search for universalities, we calculate the ratio of the condensation energy at T=0 to the Sommerfeld constant (the normal state electronic specific heat over the temperature when T it's almost zero) using two different methods: the Boson-Fermion formalism developed here, as well as an analytical expression deduced from a combination of the BCS and Ginzburg-Landau theories. We find for the Boson-Fermion formalism $E_{cond}/\gamma_0= 0.252\,T_{c}^{1.997}$, which is the same behavior described by the experimental fit of Kim et al $E_{cond}/\gamma_0= 0.2\,T_{c}^{2.06}$ and by the one recently reported by Tallon et al for overdoped cuprate superconductors; while for the Ginzburg-Landau-BCS we get the expression $E_{cond}/\gamma_0= 0.236\,T_{c}^{2}$, also in very good agreement with the partifirst method.
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All authors Juan José Valencia Acevedo, Miguel Ángel Solís Atala, Patricia Salas Casales, Israel Chávez Villalpando

Materials Science · Cross-listed from physics.comp-ph

A convolutional neural network surrogate for hierarchical homogenization: fast elastic moduli prediction of digital rocks

Hanfeng Zhai, Rasool Ahmad, Tapan Mukerji et al. (+1 more)

Digital rock physics (DRP) aims to estimate effective rock properties (e.g., elastic moduli) directly from 3D micro-CT images. However, direct numerical simulations (DNS) on high-resolution large 3D scans are often computationally prohibitive and severely limit the application of DRP. To address this bottleneck, we combine a lightweight 3D convolutional neural network (CNN) with hierarchical homogenization (HHM) and apply it to determine effective elastic moduli. In this scheme, a large rock image is divided into subcubes. The CNN replaces costly DNS by directly predicting subcube elastic moduli, while HHM upscales subcube-level predictions to the full rock. Using a shared convolutional backbone, we systematically compare three training targets: (i) full anisotropic $6\times6$ stiffness tensors, (ii) isotropic bulk and shear moduli $(K, G)$, and (iii) Hashin–Shtrikman (HS)-normalized factors. Across multiple rock types, all three models agree well with DNS results while substantially reducing the computational cost. Moreover, training from scratch on each rock type is fast enough that transfer learning is unnecessary. Across all three targets, the accuracy is comparable. In our comparative study, the HS-normalized factor offers the best overall speed–accuracy trade-off while guaranteeing physical consistency, making it a convenient default. The isotropic $(K, G)$ target is a slightly more accurate alternative.
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All authors Hanfeng Zhai, Rasool Ahmad, Tapan Mukerji, Wei Cai

Superconductivity

NMR evidence for a loop-current state with broken $C_6$ symmetry in the charge-ordered CsV$_3$Sb$_5$

X. Y. Feng, Z. Zhao, J. Dou et al. (+7 more)

Loop-current (LC) order and the associated time-reversal symmetry breaking (TRSB) are pivotal for understanding hidden magnetism and unconventional superconductivity in strongly correlated quantum materials. The recently discovered kagome metal CsV$_3$Sb$_5$ provides a unique platform for exploring these intertwined phenomena. In this study, we utilize $^{121}$Sb nuclear quadrupole resonance (NQR) and $^{51}$V nuclear magnetic resonance (NMR) measurements to investigate the possible existence of the LC order in CsV$_3$Sb$_5$. Below $T^\ast \approx 45$ K, we observe a field-independent NMR linewidth broadening at the V site in a high-quality single crystal, which indicates an internal magnetic field of 3.6 Oe at the V position. We show that this internal field arises from a static LC state that produces orbital magnetic moments $\mu_{\rm orb}$ ranging from 0.002 to 0.01 $\mu_B$. Detailed analysis suggests that the observed LC state breaks $C_6$ rotational symmetry to possess a low symmetry of $C_2$. Our results provide microscopic evidence for LC order in the charge density wave (CDW) phase of CsV$_3$Sb$_5$ and show that TRSB is intertwined with electronic nematicity, imposing stringent constraints on microscopic descriptions of the kagome CDW and its relation to superconductivity.
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All authors X. Y. Feng, Z. Zhao, J. Dou, S. Li, J. Luo, J. Yang, H. T. Yang, H.-J. Gao, R. Zhou, Guo-qing Zheng

Tuesday 23 June

Statistical Mechanics · Cross-listed from q-fin.ST

Analysis of the Principal Components of Correlation Matrices of S&P 500 Financial Data from an Econophysics Perspective

Javier Gómez Morales

This thesis analyzes the collective dynamics of the S&P 500 from an econophysics perspective, treating the financial market as a complex system. Using daily logarithmic returns of 430 companies, time-dependent Pearson correlation matrices are constructed over sliding windows and their spectral structure is studied through the leading eigenvalues and eigenvectors. Market States (MS) are identified by applying k-Means clustering to several spectral quantities: the largest eigenvalue (interpreted as the State of the Market), the squared entries of the dominant eigenvector (read as a relative participation of each stock), and truncated matrix reconstructions C^l built from the l largest eigenpairs and normalized to retain a correlation-matrix interpretation. The stability of the resulting clusters is assessed, transition matrices and their stationary vectors are computed, and the inverse participation ratio is used to quantify how participation spreads across assets. The COVID-19 episode emerges as an atypical state in the full correlation matrices; reconstructing it requires more than one principal component, and the C^2 and C^3 constructions reproduce it, particularly for window length q=40 and k=5. During crisis periods the relative participation distributes over a larger number of assets, while the 2017-2018 interval contributes to the dynamics without appearing as an isolated regime. The analysis is descriptive rather than predictive, and provides conceptual and methodological tools relevant to portfolio design and trading strategies, with natural extensions to other international exchanges.
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Strongly Correlated Electrons

Intrinsic Magnetic Excitations and Heavy-Fermion Formation in the Frustrated Mn Pyrochlore System YMn$_{2+\delta}$Zn$_{20-x}X_x$ ($X$ = In and Al) Revealed by Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance Measurements

Shunsaku Kitagawa, Kenji Ishida, Yoshihiko Okamoto et al. (+1 more)

We performed nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the microscopic electronic states of the $d$-electron heavy-fermion candidates $\mathrm{YMn_{2+\delta}Zn_{20-x}In_x}$ and $\mathrm{YMn_{2+\delta}Zn_{20-x}Al_x}$. In these compounds, magnetic fluctuations of the Mn pyrochlore lattice are expected to play an important role in heavy-fermion formation; however, excess Mn atoms complicate the interpretation of the physical properties. Our spectral analysis reveals that In substitution exhibits much higher site selectivity and introduces significantly less disorder in local structure than Al substitution. The temperature dependence of the nuclear spin-lattice relaxation rate divided by temperature $1/T_1T$ measured by $^{55}$Mn-NQR shows a clear enhancement at low temperatures, indicating the development of low-energy excitations associated with heavy-fermion formation. However, its absolute magnitude is approximately 20 times smaller than that in the related compound YMn$_2$, which hosts stronger antiferromagnetic correlations, indicating that the magnetic interactions are substantially weakened by the enlarged Mn-Mn distance. These results demonstrate that the heavy-fermion state in this system arises from the Mn pyrochlore network and is more closely associated with frustration-induced magnetic excitations with low energy than with conventional antiferromagnetic quantum-critical fluctuations.
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All authors Shunsaku Kitagawa, Kenji Ishida, Yoshihiko Okamoto, Zenji Hiroi

Strongly Correlated Electrons

The SU(N) Holstein Model

Chunhan Feng, Linh Pham, George Batrouni et al. (+1 more)

From the condensed matter physics perspective, the most natural single orbital tight-binding Hamiltonians, and hence the most widely studied, contain two fermionic species, corresponding to spin up and spin down electrons. In cold atom systems, however, SU(N) symmetry, in which $N > 2$ fermionic species reside within a single band, also occurs. In order to understand such experiments, the SU(N) Hubbard model has been increasingly studied. Here we present determinant Quantum Monte Carlo simulations of the SU(N) Holstein Hamiltonian, in which $N$ fermionic species couple to a single local phonon mode. We show that at half filling it has an insulating charge density wave phase (CDW) at low temperatures, in which empty sites alternate with sites with $N$ particles. We determine the $N=3$ CDW phase diagram in the temperature, $T$, versus electron-phonon coupling, $\alpha$, plane at fixed phonon frequency $\omega_0$ and half-filling $\rho=1.5$. The critical temperature $T_c$ for $N=3$ can be as high as twice the maximum attainable for $N=2$. We also obtain the $N$ dependence of $T_c$ for a representative, fixed, $\omega_0$ and $\alpha$.
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All authors Chunhan Feng, Linh Pham, George Batrouni, Richard Scalettar

Mesoscale and Nanoscale Physics

Defect Engineered 2D MoS2 Materials for ML-enabled Neurotransmitter SERS Detection

Md Arifur R. Khan, Besan Khader, Nicholas Trainor et al. (+4 more)

An attachment of catechol-containing neurotransmitter molecules is demonstrated on defect-engineered two-dimensional MoS2 platform, leading to activation of SERS due to molecular charge transfer. Mechanisms of neurotransmitters' bio-detection are discussed and Machine Learning methods are applied to distinguish spectra of structurally similar analytes. The SERS effect and selective docking of biomolecules are achieved through an optimized approach for defect engineering: namely, introducing the sulfur vacancies in MoS2 monolayer films via soft plasma etching led to molecular attachment driven by catechol functional groups. The quality of the sensor material was controlled by Raman, photoluminescence, and XPS characterization, thus allowing for optimization of the process of defect formation and achieving sensing selectivity. The sensor material showed no response to serotonin, confirming the specificity of attachment/SERS due to S-vacancies that regulate the strength of catechol-specific molecular adsorption. Defect-engineered MoS2 has enabled SERS detection of dopamine and epinephrine down to the sub-nanomolar range ($5\times10^{-10}$ M), with strong calibration reliability ($R^2$ = 0.95 and 0.99 for pure samples). PCA-LDA achieved 100$\%$ accuracy in distinguishing dopamine and epinephrine, which establishes defect-engineered MoS2 as a tunable, low-cost SERS platform for future sensing applications.
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All authors Md Arifur R. Khan, Besan Khader, Nicholas Trainor, Chen Chen, Joan M Redwing, Slava V Rotkin, Tetyana Ignatova

Statistical Mechanics

Accelerating Chemical Potential Calculations with Minimal Normalizing Flows

Philippe Baron and Athanassios Z. Panagiotopoulos

Chemical potentials are among the most important properties that can be obtained from a molecular simulation since they define many technologically relevant collective properties. The chemical potential of a species in solution is obtained by computing the free energy change of adding that species into a bulk system, a calculation typically very expensive for systems such as electrolytes, due to the lack of phase space overlap between "not-inserted" and "inserted" states. Recently, normalizing flows have been introduced as a way to accelerate free energy computations by learning a bijective function, constructed to be as expressive as possible, that maps the configuration space of one Boltzmann distribution onto another. This expressivity makes them difficult to train, limiting their ability to be generated "on-the-fly" for any new system, and in practice these mappings have shown only modest sampling improvements for liquids. We address these issues by introducing a "minimal" normalizing flow (MNF). This is a trainable bijective mapping that is intentionally limited in expressivity, and instead applies low-dimensional, physically informed transformations. Useful MNFs can be trained in 1 minute of GPU time due to their simplicity and our introduction of a novel training strategy. We show how calculations of chemical potentials of Lennard-Jones particle systems can be accelerated by at least 10 times with a simple radial mapping. We also apply a radial and orientational mapping to ion solvation in water, showing that MNFs can increase the effective sample size by 3 times for charging free energy calculations and 8 times for calculating free energy changes due to force field perturbations. This provides the foundation for the development of physically-informed mappings that can accelerate complex free energy calculations while retaining low training costs.
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Materials Science

Operando spectro-ptychography reveals dynamical charge-storage and degradation pathways in redox-active electrodes

Xiao Zhao, Yuchen Cao, Evan Z Carlson et al. (+13 more)

Electrochemical reactions at buried electrode-electrolyte interfaces govern how redox-active materials store and release energy. However, these reactions are difficult to visualize because chemical and morphological changes occur simultaneously over distinct length and time scales. Existing operando microscopies often require trade-offs among chemical sensitivity, spatial resolution and temporal resolution. Direct nanoscale tracking of such processes throughout extended timescale has therefore remained out of reach. Here, we develop a fast and robust operando soft X-ray spectro-ptychography platform that delivers chemical-state-resolved spatiotemporal movies of redox-active electrodes over the full battery lifetime. Applied to an alkaline Fe anode, the method reveals that reversible charge storage gives way to degradation through two competing processes: rapid hydroxide insertion that drives early reversible cycling, and slower dissolution-redeposition that redistributes Fe, enlarges FeOOH particles, and ultimately causes capacity loss. By separating fast charge-storage chemistry from slower degradation chemistry in operando and at both single-particle and particle ensemble level, this work establishes spectro-ptychography as a general approach for studying dynamic redox transformations in batteries, electrocatalysts, and other electrochemical materials.
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All authors Xiao Zhao, Yuchen Cao, Evan Z Carlson, Angel Burgos, Daniel Jacobs, Hanfeng Zhong, Lily Taylor, Haozhi Sha, Feng-yang Chen, Yu Shan, Hendrik Ohldag, Alexander Ditter, José A. Rodriguez, David Shapiro, William Chueh, Jianwei Miao

Mesoscale and Nanoscale Physics

Layer-tunable Hubbard bands probed via moiré excitons in MoSe$_2$/WS$_2$ heterostructures

Hongyu Yao, Qiao Li, Chih-En Hsu et al. (+5 more)

Moiré superlattices in transition metal dichalcogenide heterostructures provide a highly tunable platform for engineering strongly interacting states at the nanoscale. However, quantitatively determining and in-situ tuning of the underlying Hubbard parameters remains experimentally challenging. Here, we report electric-field-driven reordering of layer-specific Hubbard bands by performing optical spectroscopy on a dual-gated, 60{\deg}-aligned MoSe$_2$/WS$_2$ heterobilayer. Using two spatially distinct moiré excitons as local optical probes and tracking them as a function of carrier filling and vertical electric field, we quantitatively extract the layer-dependent on-site Coulomb repulsions, U$_M$~60 meV in MoSe$_2$ and U$_W$~30 meV in WS$_2$. Furthermore, we stabilize generalized Wigner crystal and stripe phases by electrostatically tuning the system to a type-II band alignment, shifting the ground state into the WS$_2$ layer where reduced on-site repulsion allows inter-site Coulomb interactions to dominate. Our results establish vertical electric fields as a deterministic tuning knob for layer-selective Hubbard physics, enabling device-level control of complex many-body phases.
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All authors Hongyu Yao, Qiao Li, Chih-En Hsu, Takashi Taniguchi, Kenji Watanabe, Hung-Chung Hsueh, Zhenglu Li, Andrew Y. Joe

Quantum Gases

Quantum Geometry in the Continuum: Solitons in Shallow Lattices

Koorosh Sadri and Mikael C. Rechtsman

The quantum geometry of electronic, photonic, and atomic lattice systems quantifies the distance in Hilbert space between Bloch states at neighboring lattice momenta. This quantity has profound implications for flat-band systems especially, characterizing surprising behavior such as superfluidity and superconductivity when the group velocity is zero and no transport would be expected for non-interacting particles. However, when the band is not flat, the effects of quantum geometry are often intertwined with and partly masked by the band dispersion. Here, we show that in weakly interacting bosonic systems in the critical dimension (i.e., two dimensions for Kerr nonlinearity), the deviation from critical behavior due to the presence of the lattice is governed by the quantum geometry, which is directly proportional to the fourth-order dispersion. Furthermore, we identify the family of continuous lattice potentials that saturates the bound on the quantum metric for a given effective mass tensor.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Nonlocal Quantum Phase Transitions

Alessandro Coppo, Aanal Jayesh Shah, Hadiseh Alaeian et al. (+3 more)

Phase transitions are paradigmatic examples of emergent phenomena, in which symmetries present at the microscopic level can be spontaneously broken in the thermodynamic limit. Two primary physical mechanisms can drive this symmetry breaking: thermal fluctuations in classical phase transitions and quantum fluctuations in quantum critical phenomena. Here, we introduce $nonlocal$ $quantum$ $fluctuations$ as a new fundamental mechanism to drive phase transitions. We show that entanglement shared between environmental modes can induce a correlated symmetry breaking in remote systems, independent of their spatial separation. Using the framework of driven-dissipative phase transitions, we theoretically investigate a system composed of two nonlinear quantum resonators placed at arbitrarily large spatial separations, each coupled to independent local Markovian baths. We consider the regime in which remote environmental modes are prepared in broadband entangled states. We show that near the critical point, where the susceptibility to weak perturbations diverges, quantum correlations in the environments govern the system critical behavior. While these correlations manifest locally only as effective thermal fluctuations, at the global level they give rise to an emergent nonlocal phase transition, marked by the spontaneous symmetry breaking of a collective mode shared by the two remote systems.
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All authors Alessandro Coppo, Aanal Jayesh Shah, Hadiseh Alaeian, Valentina Brosco, Roberto Di Candia, Simone Felicetti

Statistical Mechanics · Cross-listed from quant-ph

A Contactless Heat Engine Driven by Nonreciprocal Fluctuation-Induced Torques

Dhruv Shah, Kiryl Asheichyk, David Gelbwaser-Klimovsky et al. (+3 more)

We describe a contactless heat engine in which quantum and thermal electromagnetic fluctuations act as the working medium. The setup consists of two concentric cylinders held at different temperatures. The inner cylinder stably levitates within the outer one due to repulsive nonequilibrium Casimir forces. The chirality of the setup is broken by using nonreciprocal dielectric materials, akin to application of a magnetic field along the common cylinder axis. Using Rytov fluctuational electrodynamics, we show that heat transfer and torque can be expressed in terms of an angular-momentum-resolved heat flux density, $\Phi_n(\omega)$: each exchanged photon carries energy $\hbar \omega$ and angular momentum $\hbar n$. In reciprocal media contributions from modes $n$ and $-n$ cancel and there is no net torque; nonreciprocity breaks this symmetry and powers rotation of the inner cylinder. Even in the absence of contact, electromagnetic fluctuations produce a frictional torque opposing rotation that we compute. This enables computation of characteristic steady state rotations, and estimation of the engine efficiency (which remains bounded by the Carnot limit). The cylindrical setup provides a natural realization of fluctuation-induced angular-momentum transfer and a possible route toward nanoscale contactless engines.
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All authors Dhruv Shah, Kiryl Asheichyk, David Gelbwaser-Klimovsky, Noah Graham, Mehran Kardar, Matthias Krüger