Other Condensed Matter · Cross-listed from hep-th
Effective Field Theories for Material Media
Angelo Esposito, Alberto Nicolis and Riccardo Penco
We review recent progress in understanding certain aspects of condensed matter systems from a high energy theory perspective. We discuss effective field theories that describe collective bulk and localized excitations in a variety of solid and fluid systems. Particular emphasis is placed on the role played by spacetime
symmetries and their spontaneous breaking. The resulting Goldstone dynamics can be seen as underlying a wide variety of phenomena. We attempt to bridge the
language gap between subfields while underscoring the numerous conceptual similarities.
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Materials Science
BatteryMat: a hierarchical machine-learning and DFT framework for average-voltage screening of lithium-ion cathode materials
Jaehyung Lee, Charles Rhys Campbell, Kent Zhang et al. (+1 more)
Density functional theory (DFT) predicts cathode voltages accurately but does not scale to the combinatorial chemical spaces of modern materials databases, while pure machine-learning surrogates are fast but cannot guarantee thermodynamic consistency. We introduce BatteryMat, a three-tier framework that promotes single-pass average-voltage prediction with the Atomistic Line Graph Neural Network (ALIGNN) as the primary screening signal across JARVIS-DFT, then validates survivors with ALIGNN-FF force-field delithiation profiles and automated PBE+U or optB88-vdW+U supercell DFT. The exchange-correlation functional is selected automatically by spacegroup, and the lithium metal reference is recomputed in the same plane-wave basis as the cathode runs, removing a systematic offset of about 1 V present in tabulated values. Trained on 7,610 ALIGNN-FF delithiation voltages, the ALIGNN predictor reproduces the force-field labels with a mean absolute error of 0.17 V and a coefficient of determination of 0.94; this measures
distillation fidelity to the force-field protocol, not agreement with DFT or experiment. On four commercial chemistries (LiFePO4, LiMnPO4, LiMn2O4, LiCoO2) the DFT tier reproduces the experimental average voltage to within 0.3 V and the theoretical volumetric capacity to within 5%; a fifth, non-stoichiometric layered entry is carried as an edge case. The pipeline prioritises, rather than generates, existing structures: it ranks the lithium-containing JARVIS-DFT pool into 71 candidates and a scan of about 4.49 million Alexandria structures into 213, all surrogate-level leads awaiting DFT validation rather than confirmed cathodes. BatteryMat is available at https://github.com/atomgptlab/batterymat with a demo at https://atomgpt.org/battery.
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All authors Jaehyung Lee, Charles Rhys Campbell, Kent Zhang, Kamal Choudhary
Disordered Systems and Neural Networks · Cross-listed from cs.LG
Fingerprint, Not Blueprint: How Positional Schemes Set the Default Spectral Algebra of Attention
Li Hengyu
The pre-softmax score of an
attention head is a bilinear form $score(i,j) = x_i^T M x_j$ in a learned operator $M = W_q^T W_k$. Because M is generally non-symmetric, hence non-normal, it has a complex eigenspectrum and non-orthogonal eigenvectors, the regime where non-Hermitian and random-
matrix tools apply. We ask what this spectrum encodes, at three levels for previous-
token and induction
circuits. Statically, across seven pretrained models spanning three positional schemes, the strongest previous-
token heads are spectrally rotational under RoPE and non-rotational, or content-like, where position enters outside QK (learned-absolute and ALiBi); the model-level separation is perfect at every top-k examined (exact permutation $p=0.029$), and zeroing the per-frequency RoPE phase $Im(M_t)$ eliminates induction on a pre-identified previous-
token head in all three RoPE models. Dynamically, over public Pythia checkpoints every head originates at the random-
matrix (Ginibre) null; the rotational signature emerges with the behavior, not before it, and the population-median suppression that yields the final profile follows
circuit formation, so the profile is a consolidated fingerprint, not a precursor. Causally, and at toy scale, no spectral channel is necessary: constrained two-layer training reroutes around every ban with capability intact, albeit at a significant formation delay (four pre-registered contrasts, $q_BH <= 0.016$). The cost structure exposes each scheme's default: imposing
symmetry slows learned-absolute models by a factor of 2.9, whereas a RoPE head with a fully symmetric static M still routes directionally via the phase channel, impossible under absolute positions. Within the settings examined, the positional scheme sets the default spectral
algebra of an
attention head's solution: a fingerprint sculpted after function, not a hard constraint upon it.
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Mesoscale and Nanoscale Physics
2D Transport in an in-plane magnetic field
Aryaman Babbar and Sankar Das Sarma
A parallel in-plane
magnetic field could, in principle, distinguish between two competing physical scenarios for the experimentally observed density-tuned 2D metal-
insulator transition (where decreasing the carrier density leads to a crossover from an effective metal to an effective
insulator): Wigner crystallization or Anderson localization. Since the main scattering mechanism in 2D doped
semiconductors arises from screened random charged
impurities and screening in turn depends on the electronic density of states, the in-plane
magnetic field could distinguish between the two by decreasing screening through
spin polarization and this enhances the effective critical density for Anderson localization compared with Wigner crystallization. We give the general theory and provide results for the quantitative magnitudes of the
spin polarization effect on the transition density by focusing on two recent experiments [Z. Ge, et al, arXiv:2510.12009, T. Han, et al, arXiv:2604.00113], noting that the critical density may actually decrease if the dominant scattering is by short-ranged defects instead of long-ranged charged
impurities. The difference between the two cases arises from whether
spin polarization dominates screening (enhanced critical density) or the
Fermi surface (suppressed critical density).
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Mesoscale and Nanoscale Physics
Half state at $\nu_{tot}$ = -1/2 and its transition in Decoupled Twisted Double Bilayer Graphene
Ning Ma, Kenji Watanabe, Takashi Taniguchi et al. (+1 more)
The origin of the fractional state at $\nu$ = 1/2 observed in double-layer
quantum Hall systems has been under debate for decades. Because of the variation of
bilayer charge distribution and interlayer tunneling strength, the half-filling state can be attributed to a two-component(2C) or a one-component(1C) origin, which corresponds to Halperin state and Pffafian state, respectively. Here we report the magnetotransport measurement in decoupled twisted double
bilayer graphene(TDBG), which has been proved to be a promising platform for double
quantum Hall system. Fractional
quantum hall states in both odd and even denominator fillings are observed. We also found that the half-filling state occurs at zero displacement field at $\nu_{tot}$ = -1/2, which is theoretically consistent with two-component Halperin-Laughlin ({\Psi}331) state. Moreover, we report the transition from two-component state at zero D field to one-component non-Abelian state by tunning displacement field. Our observation of the half filling state and its transition from 2C to 1C state provides the tunability of decoupled twisted double
bilayer graphene and shed light on the understanding of the ground states at half-filling factor in the double
quantum Hall system.
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All authors Ning Ma, Kenji Watanabe, Takashi Taniguchi, Mitali Banerjee
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Quantum state localization in dipole-dipole interacting disordered networks
Pritam Chattopadhyay, Saikat Sur, Avijit Misra et al. (+3 more)
We study the localization of excitations in positionally disordered
spin or atom networks coupled via the realistic resonant dipole-dipole interaction (RDDI), which does not conform to a simple power law, as the spatial dependence and dissipative character distinguish it from conventional short or long-range models. Despite its partially long-ranged and radiative nature, positional disorder in the RDDI coupling leads to strong spatial localization of excitations. The interplay between coherent and dissipative couplings gives rise to nontrivial interference effects that stabilize localized modes even in open geometries. Our results uncover a
photon wavelength-induced transition from extended to localized excitation dynamics, establishing RDDI networks as a unique setting to explore the emergence of localization in realistic
quantum optical systems. Our analysis of the localized modes induced by RDDI has potential applications in coherent photovoltaics, excitonic
circuits,
quantum memory, and
quantum sensors.
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All authors Pritam Chattopadhyay, Saikat Sur, Avijit Misra, David Petrosyan, Arti Garg, Gershon Kurizki
Superconductivity
Multi-Knob Switchable Chiral Superconductivity Quartet in Rhombohedral Graphene
Zhenqi Hua, Shenyong Ye, Phatthanon Pattanakanvijit et al. (+17 more)
Chiral superconductors break orbital time-reversal
symmetry and may host topological quasiparticles with non-Abelian statistics. In rhombohedral
graphene, superconductivity develops from a
spin-valley-polarized quarter-metal (QM) parent state and features unique
magnetic hysteresis of resistance that indicates orbital time-reversal-
symmetry-breaking. Exploring and controlling the full
spin-valley
flavors of such superconductivity could enable novel superconducting and topological devices, but have remained unexplored. Here we report transport measurements on rhombohedral hexalayer
graphene (R6G), which reveal a new superconducting state (SCH) that is induced by an out-of-plane
magnetic field, in addition to
chiral superconductivity (CSC) similar to those observed in thinner layers. This SCH state emerges above 0.8 T, persists up to 1.6 T and can be switched on/off by
magnetic field $H_\perp$, carrier density $n$, and gate displacement field $D$.
Quantum oscillations and anomalous
Hall measurements show that SCH stems from a field-induced quarter-metal (QM$'$) parent phase, which carries orbital magnetization opposite to that of the zero-field QM. Across the full $(n, D, H_\perp)$ parameter space, superconductivity can be realized from all four
spin-valley isospin
flavors, establishing a switchable
chiral-
superconductor quartet in R6G. We interpret the parent-state switching as arising from competition between a Kane-Mele-like
spin-valley splitting and
magnetic-field coupling to
spin-valley-dependent
magnetic moments. Our work establishes rhombohedral
graphene as a multi-knob platform for different isospin-polarized superconductivities, which enables programmable superconducting networks with possible Majorana modes along domain walls.
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All authors Zhenqi Hua, Shenyong Ye, Phatthanon Pattanakanvijit, Gang Shi, Tonghang Han, Emily Aitken, Jixiang Yang, Junseok Seo, Haoyang Liu, Ran Hao, Kaitai Xiao, Jiaxing Guo, Vo Tien Phong, Kenji Watanabe, Takashi Taniguchi, Chunli Huang, Cyprian Lewandowski, Long Ju, Peng Xiong, Zhengguang Lu
Statistical Mechanics
Static vacancies as parametrized conformal defects in the critical $J_1$–$J_2$ transverse-field Ising chain
R. L. Silva, R. C. Silva, R. J. C. Lopes et al. (+1 more)
We revisit the problem of two static nonmagnetic vacancies in the transverse-field Ising chain with first- and second-neighbor couplings $J_1$ and $J_2$, now on the critical line, using density-
matrix renormalization-group (DMRG) calculations in open chains of up to $N=300$ sites. In contrast to the gapped regime studied previously, where the vacancy-vacancy interaction decays exponentially, along the entire
quantum critical line the interaction becomes algebraic, $|\Delta_b(r)|\sim r^{-\alpha}$, with $\alpha$ close to the universal Casimir value of unity and a weak but systematic dependence on the second-neighbor coupling, $\alpha_\infty \simeq 1.070 + 0.091\, J_2/J_1)$ across $J_2/J_1\in[0.1,1.0]$. The transmission ratio of the
spin correlator across a vacancy approaches a $J_2$-dependent plateau $T_\infty(J_2)$ that grows from $0.11$ to $0.33$ over the same range, and the Affleck-Ludwig boundary
entropy is small and approximately constant, $\log g_\infty \approx -0.073$, well above the Ising fixed-BC value $-\ln\sqrt{2}$ and close to the free-boundary value. The three observables vary smoothly and monotonically with $J_2$, consistent with a one-parameter family of partially transmissive conformal defects controlled by $J_2$. Throughout, the critical line is located using the bulk
spin-correlator exponent $\eta=1/4$, the order-parameter exponent of the Ising universality class, which provides a robust criterion in this open geometry.
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All authors R. L. Silva, R. C. Silva, R. J. C. Lopes, A. R. Pereira
Soft Condensed Matter
Sedimentation equilibrium and gravity dependent stiffness coefficients of colloidal hard-spheres
Luis G. MacDowell and Eva G. Noya
Spherical colloids with harsh repulsive forces have long been used as experimental analogs of the hard sphere model, with demonstrated good agreement with computer simulations for bulk and structural properties of the fluid, glass and
crystal phases. However, an enigmatic discrepancy remains for the
crystal-melt stiffness coefficient. Here we perform computer simulations of colloidal hard spheres under tunable buoyant mass and show that the long-standing discrepancy can be traced to a hitherto unrecognized
gravity dependent contribution of the stiffness coefficient. This effect is one practical realization of a more general result for the external field dependence of stiffness coefficients of arbitrary interfaces.
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Mesoscale and Nanoscale Physics
Correlated Insulating States in Twisted Double Bilayer Graphene Enhanced by Interfacial Effect on CrOCl
Ning Ma, Zekang Zhou, Chiara Cocchi et al. (+7 more)
Interaction between different two dimensional materials can give rise to many exotic physical phenomena which are rarely observed in intrinsic materials. Recently, several theoretical and experimental works have revealed that
magnetic proximity effect between pristine
graphene and
magnetic substrates can lead to the emergence of
quantum anomalous
Hall states and
quantum spin Hall states. However, interplay between correlated states in
graphene-based systems and
magnetic materials has seldom been studied. Here we perform the transport measurement at ultrahigh
magnetic field of twisted double
bilayer graphene (TDBG) on CrOCl (COC) substrate, which is an
antiferromagnetic material. Instead of a
magnetic-exchange effect on
graphene, we observe an enhanced correlated insulating state at half-filling factor of TDBG as a result of the charge-transfer process between TDBG and COC. The temperature and
magnetic field dependence of this enhanced state are further studied. Our results demonstrate the influence of charge-related effect at the interface, and shed a light on a new route for manipulating the correlated states in
graphene-based moiré systems using interfacial engineering.
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All authors Ning Ma, Zekang Zhou, Chiara Cocchi, Maurice Bal, Maarten van Delft, Kenji Watanabe, Takashi Taniguchi, Steffen Wiedmann, Jian-Hao Chen, Mitali Banerjee
Materials Science
Phonon-Mediated Thermal Transport in Nanocrystalline Silicon Using Machine-Learning Interatomic Potentials
Houssem Rezgui, Catalina Coll Benejam, Clivia M. Sotomayor Torres et al. (+1 more)
Understanding
phonon-mediated heat transport in structurally complex materials remains a central challenge for next-generation electronic and nanomechanical devices, where grain boundaries and interfacial disorder strongly limit thermal dissipation. Although classical interatomic potentials enable large-scale simulations, their limited transferability can lead to inaccuracies in vibrational properties and interfacial
phonon scattering. In this work, we develop a machine learning-based framework for modeling thermal transport in bulk and nanocrystalline silicon by combining Gaussian approximation potential and multi-atomic cluster expansion models with
lattice-dynamical calculations and molecular dynamics. Harmonic and anharmonic force constants derived from machine-learning interatomic potentials (MLIPs) are used within a unified Phonopy/Phono3py workflow to compute
phonon dispersions, lifetimes, and
lattice thermal conductivity, providing an internally consistent description of vibrational properties. In nanocrystalline silicon, non-
equilibrium molecular dynamics simulations directly quantify the thermal boundary resistance associated with grain boundaries and reveal its sensitivity to interfacial roughness and the underlying interatomic description. Compared with the Stillinger-Weber and Tersoff potentials, the MLIPs provide a quantitatively accurate and internally consistent description of bulk and interfacial
phonon transport, enabling better predictive modeling of nanoscale thermal transport in low-dimensional materials.
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All authors Houssem Rezgui, Catalina Coll Benejam, Clivia M. Sotomayor Torres, Miguel Pruneda
Strongly Correlated Electrons
Eclipsing Kitaev: off-diagonal exchange governs the correlated high-field phases of $\beta$-Li$_2$IrO$_3$
Vikram Nagarajan, Ioannis Rousochatzakis, Yuanqi Lyu et al. (+9 more)
We report a high-field thermodynamic study of the hyperhoneycomb Kitaev material $\beta$-Li$_2$IrO$_3$, using magnetotropic susceptibility to resolve its low-temperature field-angle phase diagram across the principal crystallographic planes in
magnetic fields up to $60$ T. Rather than evolving directly from the low-field incommensurate state into a polarized regime, the system exhibits a strongly direction-dependent sequence of correlated phases. Most notably, for fields in the $ac$-plane, we identify an additional high-field phase that is absent in the other principal planes and exists only within a restricted region of field-angle space. This phase structure is naturally explained by the competition between
magnetic field and bond-directional exchange interactions. Using a
symmetry-based description supported by microscopic calculations within the $J$-$K$-$\Gamma$ model, we show that off-diagonal $\Gamma$ exchange couples the
ferromagnetic and staggered
magnetic orders and thereby stabilizes the observed correlated high-field phases. The measured angular dependence of the critical fields is quantitatively captured by this theory, identifying $\Gamma$ exchange as the key interaction controlling the high-field response. These results clarify why the promise of a field-induced
spin liquid – the notion that suppressing
magnetic order might reveal the underlying Kitaev physics – remains unfulfilled in candidate materials: even when the Kitaev interaction is large, off-diagonal exchange stabilizes
symmetry-constrained correlated phases that instead preempt the polarized state.
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All authors Vikram Nagarajan, Ioannis Rousochatzakis, Yuanqi Lyu, Darian Hall, Augusto Ghiotto, Josue Rodriguez, Koh Yamakawa, James Analytis, John Singleton, Mun K. Chan, Natalia B. Perkins, K. A. Modic
Strongly Correlated Electrons
Charge-transfer gap size and oxygen hole content as two mechanisms controlling $T_c$ in the Emery model
Eleanor M. O'Callaghan, Nicolas Kowalski, A.-M. S. Tremblay et al. (+1 more)
Investigating the drivers of superconducting critical temperature trends in cuprates is crucial for uncovering the mechanism of high-temperature superconductivity. Here we study this problem in the canonical model of the copper-oxygen plane, the Emery model, with cellular dynamical mean-field theory. Using the Zaanen-Sawatzky-Allen diagram as a guiding framework, we systematically quantify how the maximum superconducting critical temperature $T_c^{\rm max}$ depends on the copper-oxygen energy distance and on the local repulsion on the copper orbital. Unexpectedly, $T_c^{\rm max}$ is optimized not only near the charge-transfer
insulator to metal boundary, consistent with previous findings, but also deep in the charge-transfer regime, revealing an unexplored mechanism. Then we link model parameters to physical observables, identifying the charge-transfer gap size and the oxygen hole content as two mechanisms controlling $T_c^{\rm max}$. $T_c^{\rm max}$ increases monotonically as the oxygen hole content increases and the charge gap size decreases. The oxygen hole content is the dominant variable in varying $T_c^{\rm max}$. Our work provides predictions for proposed realizations of the Emery model with ultracold atoms and a theoretical framework for understanding key experimental trends in hole-doped cuprates.
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All authors Eleanor M. O'Callaghan, Nicolas Kowalski, A.-M. S. Tremblay, Giovanni Sordi
Strongly Correlated Electrons
Correlation of maximum superconducting critical temperature with copper-oxygen energy distance and oxygen hole content in the Emery model
Eleanor M. O'Callaghan, Nicolas Kowalski, A.-M. S. Tremblay et al. (+1 more)
Identifying microscopic parameters that optimize the maximum superconducting critical temperature $T_c^{\rm max}$ in the canonical model of the copper-oxygen plane of cuprates, the Emery model, remains challenging. Using cellular dynamical mean-field theory at finite temperature, we find that for a fixed charge gap size in the parent charge-transfer insulating state, $T_c^{\rm max}$ unexpectedly increases with increasing the copper-oxygen energy distance, as this favors the transfer of electrons from oxygen to copper orbitals. We show that these findings emerge naturally in the Zaanen-Sawatzky-Allen scheme and capture observed trends in hole-doped cuprates. Overall, our study uncovers that $T_c^{\rm max}$ is optimized in the Emery model under three conditions: upon doping a charge-transfer
insulator, close to the charge-transfer
insulator to metal boundary, and deep into the charge-transfer regime. This finding indicates new paths for optimizing $T_c^{\rm max}$.
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All authors Eleanor M. O'Callaghan, Nicolas Kowalski, A.-M. S. Tremblay, Giovanni Sordi
Soft Condensed Matter
Dimensional Crossover of Thermal Transport in Nanoconfined Liquids Driven by the Interplay of Quasi-One-Dimensional Structure and Wall Dissipation
Kenta Hisamoto, Yusei Kobayashi, Takahiro Ikeda et al. (+2 more)
Heat transport in nanoconfined
liquids can deviate from ordinary
Fourier behavior because confinement alters
liquid structure and interfacial dissipation. Although such changes may lead to quasi-one-dimensional transport or overdamped sound relaxation, the conditions under which length-dependent transport persists remain unclear. Here we use molecular dynamics simulations of monatomic
liquid argon confined in carbon nanotubes with systematically varied radii and lengths. We find a radius-controlled crossover: length-dependent axial thermal conductivity persists over long tube lengths in single-file and single-shell states, but is strongly truncated or nearly saturated once mixed-shell or multilayer packing develops. This crossover is accompanied by the loss of clear acoustic-like axial modes and enhanced wall–
liquid friction. Thus, tube radius controls whether length-dependent heat transport persists or is truncated by coupling confined-
liquid structure to wall-induced dissipation.
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All authors Kenta Hisamoto, Yusei Kobayashi, Takahiro Ikeda, Eiji Yamamoto, Masashi Yamakawa
Strongly Correlated Electrons
Instabilities of Fermi Liquids with Arbitrary Forward Scattering: Exact Approach
Dmitry Miserev, Joel Hutchinson, Herbert Schoeller et al. (+2 more)
In this work, we consider $N$-fold degenerate $D$-dimensional electron gas with spherical
Fermi surface and arbitrary forward-scattering density-density interaction transferring small momentum compared to the
Fermi momentum $k_{\mathrm{F}}$. The dimensional reduction that is mathematically equivalent to the Haldane patch construction and similar multidimensional bosonization techniques, provides a natural map of two-point $D$-dimensional correlation functions (
fermion Green function, susceptibilities etc.) onto effective one-dimensional (1D) correlators with the same diagrammatic structure, which can be evaluated exactly within a 1D bosonizable (Gaussian) theory. We then apply this formalism to evaluate the
fermion Green function, pair and charge/
flavor susceptibilities, as well as the composite correlation functions for the case of a finite-range interaction, where the interaction range $R_{\mathrm{s}} \gg 1/k_{\mathrm{F}}$ is large compared to the
Fermi wavelength. First, we find that the single-particle spectral function remains
Fermi-
liquid-like which is fully consistent with the previous research. In contrast to the single-particle sector, the many-body channels are efficiently dressed by finite-range interactions, and this dressing is fully equivalent to the one-loop renormalization group (RG), which is also in line with previous multidimensional bosonization results. Within the forward-scattering model, stable long-range order is not possible, and relevant susceptibilities demonstrate singular power-law scaling with temperature $T$ at $T \to 0$. The rest of the abstract is in the PDF.
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All authors Dmitry Miserev, Joel Hutchinson, Herbert Schoeller, Jelena Klinovaja, Daniel Loss
Strongly Correlated Electrons
Skyrmion Phase Control by Magnetic Dipole-Dipole Interaction and Electric Field in Centrosymmetric Materials
Raz Rivlis, Alexander Petrović and Yuri Dahnovsky
Establishing precise control over the helicity and spatial configuration of
magnetic skyrmions will be essential to realize their promise in classical, analog and
quantum computation applications. In this work, we explore the role of
magnetic dipole-dipole interactions, external electric fields, and
magnetic fields in controlling these parameters within a triangular
lattice centrosymmetric skyrmion host. We demonstrate that dipole-dipole interactions strongly favor Bloch helicity. Notably, a zero
magnetic field skyrmion phase appears upon raising the dipole-dipole coupling strength, with substantial potential for cost-effective
quantum device applications. We also report the emergence of a meron/antimeron
lattice phase, in the absence of any Dzyaloshinskii-Moriya interaction. In contrast, applied electric fields stabilize high density Néel skyrmion
crystals. The interplay between dipole-dipole interactions and external electric fields creates a continuous transition between the two skyrmion types, rather than an abrupt switch. Applied electric fields can therefore be used as a continuous tuning mechanism for skyrmion helicity, and hence a control handle for tuning two-level systems in skyrmion
qubits.
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Materials Science · Cross-listed from physics.optics
Terahertz-driven four-wave mixing at glass surfaces: Probing vibrational resonances and structural regimes
Mathias Hedegaard Kristensen, Jérôme Degert, Theo Guillaume et al. (+3 more)
Disordered materials such as glasses exhibit complex structural dynamics that are challenging to probe with conventional spectroscopies. We demonstrate that terahertz-driven four-wave mixing (FWM) at glass surfaces provides direct access to low-frequency vibrational modes and structural
evolution in amorphous solids. Applied to a compositional series of PbO-silicate glasses (20-54 mol% PbO), this technique resolves distinct contributions from collective
Boson-peak excitations and Pb-O / Si-O network stretching modes, and tracks their systematic
evolution across structurally distinct compositional regimes. The dominant vibrational frequency blueshifts with PbO content, reflecting the progressive
evolution of the Pb$^{2+}$ network role from silicate-modifier to ward network-former. A pronounced enhancement of the FWM signal near 44 mol% PbO coincides with the emergence of medium-range Pb-Pb correlations, while in-plane-to-out-of-plane FWM intensity ratio ($I_{\rm SS}/I_{\rm PS}$) tracks $\chi^{(3)}$ tensor anisotropy tied to Pb$^{2+}$ lone-pair spatial correlations. The non-monotonic peak in both observables at 44 mol% PbO - a composition where NMR finds no change in local Pb-O coordination and Pb-O-Pb free-
oxide linkages are negligible - provides direct evidence that a collective lone-pair reorganization occurs in the medium-range structure independently of nearest-neighbor bonding. These results establish terahertz-driven FWM as a bulk-sensitive, near-surface depth-confined ($\sim$50 nm) nonlinear spectroscopy sensitive to vibrational and electronic structural fingerprints inaccessible to linear infrared, Raman, and terahertz time-domain probes.
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All authors Mathias Hedegaard Kristensen, Jérôme Degert, Theo Guillaume, Emmanuel Abraham, Laetitia Dalstein, Eric Freysz
Materials Science · Cross-listed from physics.chem-ph
Economised path integrals
Zezhu Zeng and David E. Manolopoulos
The Hessian of the ring
polymer spring potential in the standard Trotter path integral is a $P\times P$ symmetric circulant
matrix with a centroid
eigenvalue of zero. All such
matrices commute and are diagonalised by the same bead to normal mode transformation
matrix, and their
eigenvalues contain $\lceil P/2\rceil-1$ degenerate pairs by
symmetry. However, this still leaves some freedom to improve on the Trotter approximation: one can optimise the remaining $\lfloor P/2\rfloor$ independent non-zero normal mode frequencies to fit the exact
quantum mechanical radii of gyration of harmonic ring
polymers with frequencies in the range $0\le\omega\le\omega_{\rm max}$, where $\omega_{\rm max}$ is the maximum physical frequency in the problem of interest. The optimisation involves solving a simple least squares problem for the optimum (economised or "Eco") internal mode frequencies. The remainder of the calculation then proceeds in the same way as a Trotter path integral calculation. An example application to hexagonal ice shows that the convergence of the Eco path integral is comparable to that of the 4th order Suzuki-Chin path integral, but with purely 2nd order Trotter effort. There is no need to calculate the projected Hessians that arise in the Suzuki-Chin method by finite differences, there is no need to develop any new
estimators for observables, and once the Eco frequencies have been calculated the implementation of the Eco path integral involves changing just a few lines of a Trotter path integral code. To provide a more impressive example we have implemented the Eco method in GPUMD and used it to converge the (negative) thermal expansion coefficient and the constant pressure heat capacity of MOF-5 with a machine-learned neuroevolution potential.
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Other Condensed Matter
Spontaneous emission of light by non-equilibrium phonons
J. Plo, P. Valvin, M. Moret et al. (+8 more)
When a system is brought out of
equilibrium by an external excitation, its relaxation to thermodynamic
equilibrium generates
phonons. These non-
equilibrium phonons degrade via cascaded anharmonic decay processes, progressively leading to a thermal population of
phonons following a Bose-Einstein distribution at the system temperature. Preceding heat dissipation by convection, conduction and incandescence, this early phase of the relaxation dynamics is commonly assumed to be exclusively non-radiative. Here, we demonstrate that the radiative emission by
phonons can be an efficient relaxation pathway competing with the intrinsic anharmonic decay. Optical spectroscopy under femtosecond two-
photon excitation in boron nitride unveils a photoluminescence signal in the mid-infrared spectral range, stemming from the spontaneous emission of light by non-
equilibrium phonons. This observation of non-thermal radiation from
phonons introduces a new paradigm for out-of-
equilibrium physics, mid-infrared optics, and thermal management.
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All authors J. Plo, P. Valvin, M. Moret, T. Taliercio, J. Batista, T. Sohier, A. Vasanelli, C. Sirtori, B. Gil, W. Desrat, G. Cassabois
Superconductivity
Effect of charge-imbalance potential relaxation on the high-frequency vortex dynamics and kinetic inductance of superconducting circuits
R. I. Kinzibaev, V. S. Stolyarov and A. S. Mel'nikov
We show that relaxation of the charge-imbalance potential plays a key role in the retarded dynamics of Abrikosov
vortices in a type-II superconducting sample carrying a microwave current. Starting from the time-dependent Ginzburg–Landau equations we derive the
vortex equation of motion accounting both the dissipation and retardation effects. The retardation is governed by the dynamics of the charge-imbalance potential and reveals itself at characteristic timescales diverging near the superconducting critical temperature $T_{c}$. These retardation effects in
vortex dynamics strongly affect the kinetic inductance of superconducting
circuits being, thus, responsible for the
magnetic field dependence of characteristics of different superconducting devices in the high frequency range.
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Soft Condensed Matter
Hybrid Dynamical Simulation Reveals Apparent Stiffening of Flexible Protein Lattices Driving Membrane Bending
Samuel L. Foley and Margaret E. Johnson
Membrane-deforming
protein lattices play a central role in essential and pathogenic remodeling processes, including clathrin-mediated endocytosis and viral budding. Simulating these systems at biologically relevant length and time scales requires mesoscale approaches that preserve structural detail while avoiding the computational cost of atomistic resolution. Here, we present a hybrid simulation framework that couples a particle-based flexible
protein lattice to a continuum membrane model, enabling systematic investigation of how
lattice geometry and
rigidity influence dynamic membrane remodeling. We validate the coupled model by comparing simulation results with theoretical predictions for membranes under increasing tension. Using buckling-based deformations of pre-assembled clathrin
lattices, we quantify the
lattice flexural
rigidity and establish a direct relationship between the force constants in the coarse-grained energy and the emergent mechanical properties of the
lattice. We then compare this flexural
rigidity to an effective
rigidity commonly used in continuum descriptions of sphere-forming
protein assemblies. Although the flexural
rigidity is set solely by the energy function, the effective
rigidity depends on
lattice size and connectivity, with the two measures converging only for weakly connected
lattices. As a result, the effective
rigidity relevant for spherical bud formation increases as the
lattice grows. This size-dependent stiffening highlights the importance of structural details in interpreting
lattice mechanics and cautions against assuming a single constant stiffness throughout assembly. We demonstrate the generality of the method by applying it to pre-assembled viral
lattices generated with NERDSS. This work provides a validated framework for simulating how deformable, stable
protein assemblies of diverse geometry couple to membrane dynamics and remodeling.
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Mesoscale and Nanoscale Physics
Radio frequency readout and control of Ge/SiGe hole spin qubits with a global accumulation gate
Tien-Ho Chang, Chi-Wei Lee, Jian-Chang Zeng et al. (+12 more)
Hole
spin qubits in undoped Ge/SiGe
quantum well structures have advanced rapidly in performance and scalability. However, stringent multi-layer patterning and overlay requirements of conventional overlapping-gate devices create a bottleneck for academic proof-of-concept experiments involving few-
qubit devices. Here we present fabrication and measurements of Ge/SiGe
spin qubit devices with a global accumulation gate and single-layer depletion fine gates, which substantially reduce fabrication complexity. With careful design of the gate-2DHG capacitance, we demonstrate RF-based single-shot
spin readout and coherent control of two single-
spin qubits. We also characterize the
spin coherence times and exchange tunability, which are similar to those reported in recent overlapping-gate Ge/SiGe
spin qubit devices. By simplifying fabrication without sacrificing performance, our approach offers a more accessible device design for
spin-based
quantum technology research.
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All authors Tien-Ho Chang, Chi-Wei Lee, Jian-Chang Zeng, Chia-Hao Wei, Ching-Shiang Wang, Fu-Yuan Gu, Guan-Yu Yang, Ruei-Syuan Chiang, Ho-Chun Wu, Ming-Hao Lee, Ming-Wen Chu, Guang Li Luo, Ta-Chun Cho, Shawn S. H. Hsu, Tzu-Kan Hsiao
Superconductivity
Anomalously high quasiparticle thermal conductivity in the underdoped cuprate superconductor HgBa$_{2}$CuO$_{4+\delta}$
Jordan Baglo, Quentin Barthélemy, Étienne Lefrançois et al. (+4 more)
The single-layer cuprate
superconductor HgBa$_{2}$CuO$_{4+\delta}$ (Hg1201) is an ideal candidate for investigating many properties of cuprates with minimal disorder and without the complication of multiple CuO$_2$ layers. Here we measure the in-plane longitudinal thermal conductivity $\kappa$ of underdoped Hg1201 ($T_c$ = 76 K, $p$ = 0.11) at dilution refrigerator temperatures to extract the nodal quasiparticle velocity ratio $v_F/v_\Delta$. Assuming contributions from only a single line node per quadrant on the
Fermi surface leads to a value of $v_F/v_\Delta$ = $23 \pm 3$, anomalously large compared to other cuprates at similar dopings. In conjunction with the anomalously high quasiparticle specific heat of Hg1201 in the normal state reported previously at a similar doping, this points to more than one
Fermi surface sheet crossing the nodal line, suggesting the presence of more than the single small electron pocket detected by
quantum oscillations.
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All authors Jordan Baglo, Quentin Barthélemy, Étienne Lefrançois, Anne Forget, Dorothée Colson, Cyril Proust, Louis Taillefer
Statistical Mechanics
Robust q-negative Multifractal Detrended Cross-Correlation Coefficient
Thiago B. Murari, José Fernando F. Mendes, Hernane B. B. Pereira et al. (+1 more)
The multifractal detrended cross-correlation coefficient $\rho_q(n)$ is widely used to investigate scale-dependent interactions, but its application to negative fluctuation orders is affected by numerical instabilities, unbounded values, and interpretational difficulties. We propose a Signed Multifractal Detrended Cross-Correlation Coefficient, $\rho_{\mathrm{SMFDCCA}}(n,q)$, an amplitude-conditioned correlation observable for multifractal detrended analysis, based on locally normalized detrended correlations and regularized fluctuation amplitudes. The proposed coefficient preserves the sign of local interactions, remains strictly bounded within $[-1,1]$ for both positive and negative values of $q$, and eliminates the corrective procedures required by previous approaches. Validation using independent fractional Gaussian noise confirms the absence of spurious cross-correlations and the numerical stability of the method. Applications demonstrate that the proposed observable resolves how cross-correlations evolve jointly with temporal scale and fluctuation amplitude, revealing scale- and amplitude-dependent correlation structures, including stronger synchronization during large fluctuations in stock-
market indices and heterogeneous coupling patterns in temperature records.
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All authors Thiago B. Murari, José Fernando F. Mendes, Hernane B. B. Pereira, Marcelo A. Moret
Superconductivity
Decoupling Josephson Coupling and Supercurrent Nonreciprocity in Twisted NbSe2/NbSe2 van der Waals Junctions
Seung-Gi Lee, Kwon-Neong Jung, Jae-Kuen Kim et al. (+4 more)
The microscopic origin of supercurrent nonreciprocity in van der Waals Josephson junctions remains under active debate, particularly regarding the role of twist-angle engineering in layered
superconductors. Here, we investigate superconducting transport in twisted NbSe2/NbSe2 vertical Josephson junctions fabricated by dry transfer with controlled crystallographic
alignment and chemically clean interfaces. High-resolution transmission electron microscopy is employed to directly determine the twist angle and assess interface quality. While the Josephson coupling strength exhibits a pronounced dependence on twist angle, with characteristic voltages maximized near crystallographically equivalent orientations and suppressed at intermediate angles, the supercurrent diode efficiency remains negligibly small and shows no systematic twist-angle dependence. In contrast, enhanced diode-like responses emerge only in weakly coupled junctions exhibiting interfacial disorder and reduced transparency. Deliberate interface degradation further amplifies the apparent nonreciprocity, yielding diode efficiencies approaching 30% together with an irregular
magnetic-field-strength dependence. These results establish a clear decoupling between Josephson coupling and supercurrent nonreciprocity in twisted NbSe2/NbSe2 junctions. Our findings identify interface disorder, rather than twist-angle-controlled momentum matching, as the dominant origin of the observed diode response and provide a critical
benchmark for interpreting nonreciprocal superconducting transport in van der Waals Josephson devices.
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All authors Seung-Gi Lee, Kwon-Neong Jung, Jae-Kuen Kim, Jae-Chun Jeon, Jiho Yoon, Stuart S. P. Parkin, Kun-Rok Jeon
Mesoscale and Nanoscale Physics
From Valley Filtering to Superconducting Diode Effect in Spin-Orbit Coupled Graphene Junctions
F. Bonasera, G. A. Falci, E. Paladino et al. (+1 more)
We study the transport properties of proximitized
graphene, which can acquire a
spin-orbit coupling by the proximity effect with a substrate. We focus on the ballistic and zero temperature limits, making use of a tight-binding procedure based on the KWANT Python package. We first find key results on valley-filtering properties and asymmetric edge transport in
spin-orbit coupled
graphene single junctions, and then move to the analysis of the superconducting transport in a
graphene Josephson junction, in the short junction limit. We study the relative contribution of edge modes for different edge terminations and some degree of edge disorder, and also analyze the
magnetic interference pattern that arises when threading the junction with a perpendicular
magnetic field. We find residual supercurrent at high
magnetic fluxes, due to the localized nature of transport in the junction, and a strong non-reciprocal transport that leads to a significant Josephson diode effect.
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All authors F. Bonasera, G. A. Falci, E. Paladino, F.M.D. Pellegrino
Mesoscale and Nanoscale Physics
Composite-Fermion Study of Cavity-Modified Fractional Quantum Hall Excitation Gaps
Dalin Boriçi, Nicolas Regnault and Cristiano Ciuti
We investigate how cavity-mediated attractive electron-electron interactions modify the excitation gaps of fractional
quantum Hall states within the composite-
fermion framework. We compute both the neutral magnetoroton excitation spectrum and the charged excitation gap relevant to transport experiments for the Laughlin $\nu=1/3$ and $\nu=1/5$ states. We consider a
spin-polarized lowest-Landau-level model in which the interaction is mediated by a cavity mode with a spatially uniform
vacuum-field gradient and a finite interaction range controlled by a long-distance cutoff. Finite-size scaling reveals that the transport gap is consistently enhanced by the cavity-induced interaction, with the gap enhancement scaling quadratically with the electron number and with the fourth power of the
vacuum-field gradient. By contrast, the magnetoroton spectrum exhibits a richer dependence on the interaction range. The high-$k$ magnetoroton gap is enhanced for all interaction ranges considered, consistent with its close connection to the charged excitation gap, even with the long-range character of the interaction.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Calculating strongly correlated ground states from the non-Markovian dissipative dynamics of Gaussian fermions
Giuliano Chiriacò
We introduce a mapping between the ground state of interacting fermionic
Hamiltonians and the non-
equilibrium steady state of a purely dissipative open
quantum system. Within the framework of third quantization, we map the
Fermi-Hubbard
Hamiltonian onto Lindblad jump operators acting on Majorana
fermions. Remarkably, both hopping and interaction terms map onto jump operators that preserve the Gaussianity of Majorana
fermions along individual
quantum trajectories. As a result, the dynamics can be unravelled and each trajectory can be simulated efficiently using only two-point correlation functions, with a computational cost that scales polynomially with system size. We further show that finite particle number requires negative dissipative rates, leading to an intrinsically non-Markovian dynamics. The corresponding trajectory unravelling involves both positive and negative
stochastic weights and exhibits a sign problem and large fluctuations, so that convergence requires an exponentially large number of trajectories. The overall computational cost remains exponential in system size despite the efficient Gaussian representation of individual trajectories, but is crucially dependent on the computational complexity of the non-Markovian unravelling, motivating further studies on the efficiency of such unravellings.
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Statistical Mechanics · Cross-listed from hep-th
Determination of thermodynamics from entanglement entropy in the finite-density O(N) model
Niko Jokela, Aatu Rajala and Tobias Rindlisbacher
We nonperturbatively compute Rényi
entropies for strip-shaped subregions in the three-dimensional O(4) model at finite density on the
lattice. By using a dual variable representation and a tailored worm
algorithm, we circumvent the sign problem when sampling the grand canonical ensemble. In the limit of large subregions, we also establish a direct, quantitative relationship between the derivative of
entanglement entropy with respect to the size of the entangling region and the thermal
entropy density for general
quantum field theories, providing a new way to study their thermodynamics. We corroborate this argument with our
lattice results by demonstrating that, in the appropriate limit, the derivative of
entanglement entropy satisfies the same Maxwell relation as the thermal
entropy density.
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