Quantum Gases
Collective dynamics of harmonically trapped 1D quantum droplets under linear gravitational-like confinement
Saurab Das, Jayanta Bera and Ajay Nath
We investigate the dynamics of harmonically confined
quantum droplets in a binary Bose Einstein condensate within the one dimensional extended Gross Pitaevskii framework, including LHY corrections, under a constant linear (gravitational like) potential. By analyzing the COM and width dynamics, we show that the monopole (breathing) mode remains governed by the harmonic confinement, with a frequency asymptotically insensitive to the linear perturbation, demonstrating the robustness of internal collective excitations against uniform external forcing. In contrast, the COM exhibits interaction-dependent transport, with weak confinement producing large susceptibility and rapid displacement, whereas strong confinement suppresses transport even under large forcing. The COM response decreases monotonically with increasing trap frequency. We further characterize the evolving
quantum state through the
quantum Fisher information and Wigner quasi-probability distributions, showing that the linear potential enables controlled generation of states with enhanced metrological sensitivity over finite times, while stronger confinement shifts the onset of the high-sensitivity regime to larger forcing strengths. Numerical simulations based on the split-step
Fourier method confirm the dynamical stability of the obtained solutions. These results illustrate the impact of linear gravitational like trap on the collective excitations, transport, and
quantum metrological properties of 1D ultradilute
quantum fluids.
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Soft Condensed Matter
Stochastic process model of rough surface contact
Yang Xu and Yunong Zhou
The
stochastic process model of rough surface contact, widely known as Persson's theory of contact, serves as a representative multi-scale model that has been extensively applied across various fields of tribology. In this chapter, we briefly introduce the background of the development of Persson's theory of contact. We thoroughly discuss Persson's theory for purely normal elastic contact, with a special focus on solving the probability density of the contact pressure and the interfacial gap using partial differential equations. Subsequent applications of these fundamental results in addressing more complex interfacial properties in other fields of tribology are also examined. Finally, several recommendations regarding future studies of Persson's theory are proposed. This review article is expected to assist researchers in quickly familiarizing themselves with the current state of the art of Persson's theory and to attract more
attention from tribologists and solid mechanicians, thereby contributing to the development and application of Persson's theory of contact.
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Materials Science
Self-organized defect clustering and concentration-dependent vacancy diffusion in MoS$_2$
Aaron Flötotto, Benjamin Spetzler, Martin Ziegler et al. (+2 more)
Sulfur vacancy migration has a crucial impact on electronic transport and the functional behavior of MoS$_2$-based devices such as memristors and memtransistors. According to recent atomistic simulations, vacancy migration proceeds via cooperative, vacancy-assisted sulfur jumps, implying strongly correlated defect dynamics. Here, we investigate the collective behavior of sulfur-vacancy clusters in MoS$_2$ using kinetic Monte-Carlo simulations with transition rates derived from machine learning interatomic potential molecular dynamics simulations. We identify three transport regimes: At low concentrations, vacancies are immobile or confined within small clusters, whereas at high concentrations, classical diffusive transport with a constant
diffusion coefficient is observed, and vacancies aggregate into anisotropically extended clusters. A well defined intermediate regime is characterized by clusters merging into a connected, fluctuating network with a concentration-dependent
diffusion coefficient. This regime is characterized by a broad distribution of cluster sizes. The strong dependence of the vacancy
diffusion coefficient on the average defect concentration provides new insights into the origin of memristive behavior observed in MoS$_2$.
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All authors Aaron Flötotto, Benjamin Spetzler, Martin Ziegler, Erich Runge, Christian Dreßler
Mesoscale and Nanoscale Physics
Avoiding Dilution: Using Diffusion and Vision Transformers to resolve Majorana Features in Nanowires at High Temperature
Jacob R. Taylor, Haining Pan, Jay D. Sau et al. (+1 more)
Identifying Majorana zero modes in
semiconductor–
superconductor nanowires requires ultra-low temperature transport measurements in dilution refrigerators, making device screening slow and resource-intensive. Here, we investigate whether high-temperature conductance data can be used to infer low-temperature Majorana nanowire properties before committing devices to dilution-refrigerator characterization. We generate paired high- and low-temperature conductance simulations for disordered Majorana nanowires and train neural networks to perform two related tasks. First, we use a Shifted Window U-Net
Transformer diffusion-inspired architecture to reconstruct low-temperature conductance from thermally broadened high-temperature measurements, achieving high-fidelity recovery with $R^2 \approx {0.95}$ for local conductance and $R^2 \approx {0.91}$ for nonlocal conductance. Second, we train a
Video Vision Transformer-based network to predict the low-temperature topological visibility directly from high-temperature conductance, obtaining $R^2 \approx {0.80}$. These results demonstrate that machine-learning models can recover and infer low-temperature Majorana features from experimentally easier high-temperature data, providing a practical route for rejecting poor devices early thus avoiding slow and resource-intensive dilution refrigeration for non-promising devices. This high-temperature screening approach could substantially accelerate the experimental feedback loop for Majorana nanowire device development.
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All authors Jacob R. Taylor, Haining Pan, Jay D. Sau, Sankar Das Sarma
Mesoscale and Nanoscale Physics
Tomographic flow regime vs even-odd effect for the magnetotransport in the Corbino geometry
Grigory A. Starkov
In two dimensions, the
geometric constraints due to Pauli blocking and conservation laws lead to the even-odd effect exhibited by the electron-electron scattering lengths: electron-electron collisions are more efficient at relaxing the even angular harmonics of the distribution function than the odd ones. Inspired by a recent experiment on the magnetotransport in the Corbino disk geometry, we numerically analyze the electron flows in this geometry across all the regimes. We predict a clear signature of the even-odd effect - enhancement of the resistance sensitivity $\partial R/\partial(B^2)$ at small
magnetic fields $B\rightarrow 0$. This enhancement is most prominent at the crossover from the ballistic to the tomographic regime, and gradually disappears when the temperature is further increased. Our estimates suggest that in the temperature range of the experiment, the effect should be small. This implies that the attribution of the anomalous scaling of the kinematic viscosity, that was observed in the experiment, to the even-odd effect might need more careful consideration. As a side note, we show how the method of characteristics can be extended to treat the long-lived odd harmonics, which allows one to recast the linearized Boltzmann equation as a system of integral ones.
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Materials Science
Spot Profile Analysis Low Energy Electron Diffraction of Plasma-Enhanced Chemical Vapor Deposition Grown Epitaxial Few-Layer Graphene on Sapphire
Niels Ganser, Marko A. Kriegel, Umut Kaya et al. (+6 more)
We demonstrate the use of high-resolution spot-profile analysis low-energy electron diffraction to determine the mean grain size of
plasma-enhanced chemical vapor deposition grown few-layer
graphene on sapphire (Al$_2$O$_3$). The diffraction patterns exhibit broadened
graphene spots, pronounced diffuse scattering, and azimuthally extended features, indicating finite crystallite size and rotational disorder. By analyzing the finite-size broadening of the specular (00) spot with an Airy-type diffraction profile, we determine a mean grain diameter of 3.7$\,$nm for the as-grown
graphene layer. Post-growth annealing under ultrahigh-
vacuum conditions increases the mean grain size to about 5.7$\,$nm and 6.8$\,$nm, respectively. These results establish SPA-LEED as a sensitive reciprocal-space method for quantifying the structural coherence of directly grown
graphene on insulating substrates.
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All authors Niels Ganser, Marko A. Kriegel, Umut Kaya, Jixi Zhang, Rodney D. L. Smith, Marika Schleberger, Wolfgang Mertin, Gerd Bacher, Michael Horn-von Hoegen
Disordered Systems and Neural Networks
Star-triangle duality estimates for triangular and honeycomb permutation models
Masayuki Ohzeki
We study a duality analysis in conjunction with the
star-triangle transformation for symmetric-group permutation models on the triangular and honeycomb
lattices. The calculation is motivated by the permutation-model description of random tensor networks and by earlier duality analyses of replicated
spin glasses. The essential point is that the finite-basis unit is not a bare bond but a
star-triangle block. Our analysis estimates the critical bond dimension for the honeycomb
lattice to be 2.634929344884, and the associated single-bond duality relation yields the triangular-
lattice estimate 1.475661534848.
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Strongly Correlated Electrons
Sizable Ligand-Mediated Bond-Dependent Interactions in a Spin-1 Triangular Antiferromagnet NiI$_2$
Hao Xu, Weiqin Zhu, Shufan Cheng et al. (+11 more)
The bond-dependent anisotropic Kitaev interactions are the key for the Kitaev model, which has attracted intense interest for its potential to host
quantum-
spin-
liquid states and fractional excitations. However, experimental realizations of such interactions remain scarce. Here, we investigate the
magnetic excitations of NiI$_2$, a van der Waals magnet with
spin $S=1$. By combining inelastic
neutron scattering, magnetization measurements,
magnetic structure analysis, first-principles calculations, and linear-
spin-wave simulations, we identify a minimal model that features substantial Kitaev and off-diagonal $\Gamma$ interactions, which together stabilize the canted
magnetic ground state and open a gap in the
spin-wave spectrum. Notably, these interactions arise from strong
spin-orbit coupling on the ligand ions, despite the quenched orbital moment of the
magnetic Ni$^{2+}$ ions. Our results provide compelling experimental evidence for the ligand-driven Kitaev mechanism. This demonstrates a concrete pathway to generating strong bond-dependent anisotropy in systems where the
magnetic ions themselves have weak
spin-orbit coupling, thereby substantially broadening the range of potential Kitaev materials.
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All authors Hao Xu, Weiqin Zhu, Shufan Cheng, Yanyan Shangguan, Song Bao, Junbo Liao, Bo Zhang, Zihang Song, Shuai Dong, Maofeng Wu, Stanislav E. Nikitin, Travis J. Williams, Changsong Xu, Jinsheng Wen
Strongly Correlated Electrons · Cross-listed from quant-ph
Lakshya Nagpal, Nishith Reen and S.R. Hassan
Exact
fermion to
qubit transformations are conventionally regarded as algorithmic tools that translate many-body
Hamiltonians into
qubit representations for
quantum simulation. Here we show that they also define intrinsic
geometric representations whose structure encodes physically meaningful information beyond spectral equivalence. We develop a
geometric framework based on weighted hypergraphs and coupling space representations constructed from the Bravyi–Kitaev (BK) and Xia–Bian–Kais (XBK) encodings. Within the BK representation, we introduce a
geometric observable that compares the algebraic connectivities of the kinetic and interaction hypergraphs, derive its exact analytical dependence on interaction strength, and uncover two
geometric universality classes together with an exact spectral organization originating from the binary tree architecture of the encoding. The complementary XBK representation describes the
evolution of encoded
Hamiltonians through probability measures in coupling space, where optimal transport quantifies interaction-driven reorganization independently of the spectral analysis. Applications to the Hubbard, spinless tV , single
impurity Anderson, and Kitaev models demonstrate that these connectivity and transport based
geometric descriptions consistently capture the structural
evolution of encoded
quantum Hamiltonians across distinct classes of many-body systems. Our results establish hypergraph geometry as a new framework for understanding
fermion-to-
qubit encodings,revealing that they serve not only as computational mappings but also as
geometric representations of
quantum many-body
Hamiltonians.
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Strongly Correlated Electrons
Optimization dynamics of Transformer backflow neural quantum states for the two-dimensional Hubbard model
Zong-Yu Liao, Jia-Qi Wang, Rong-Qiang He et al. (+1 more)
Building on the multi-determinant
Transformer backflow neural
quantum state (NQS) ansatz and the associated multi-stage training workflow for the doped two-dimensional Hubbard model, we investigate how the optimization dynamics of the NQS depend on several key optimization and architectural hyperparameters. The workflow consists of neural-network backflow (NNB) initialization, supervised
Transformer pre-training, and main energy optimization using the Moment-Adaptive ReConfiguration Heuristic (MARCH) within variational Monte Carlo. Using the doped $4\times4$ periodic Hubbard model at $U=8$ as a baseline, we examine how the update-norm threshold,
Transformer width, number of determinant channels, and Monte Carlo batch size affect convergence. We find that a moderate update constraint improves the efficiency of MARCH optimization, larger
Transformer width and more determinant channels improve the expressive capacity of the ansatz, and larger Monte Carlo batches reduce sampling noise in the update direction. We further test the same workflow at half filling, weaker interaction strength, open boundary conditions, and on a larger $8\times8$ doped
lattice. These results identify practical optimization trends for
Transformer backflow NQSs and highlight the balance between ansatz expressivity, MARCH update stability, and Monte Carlo sampling quality.
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All authors Zong-Yu Liao, Jia-Qi Wang, Rong-Qiang He, Zhong-Yi Lu
Mesoscale and Nanoscale Physics
Pablo A. Morales
In a flat crystalline membrane, the low-energy spectrum is dominated by a flexural mode that does not couple to
phonon Hall viscosity. We show that static
curvature converts normal motion into in-plane strain and thereby opens a
Hall-active flexural channel. Tracefree
curvature couples directly to
Hall-active shear, while mean
curvature acts indirectly through the shear generated by ordinary in-plane elasticity. Together, these channels generate in-plane
phonon angular momentum along the surface normal. For statistically isotropic shallow ripples, the time average has a definite sign fixed by the
Hall viscosity, producing a steady field-odd torque proportional to the mean-square
curvature. Using the measured bulk
Hall viscosity of $\alpha$-RuCl$_3$ to set the scale, we estimate a torque of order $10^{-22}\,\mathrm{N\,m}$ for a few-layer membrane, within reach of demonstrated torsional sensors. The same flexural-to-shear response provides a probe of
phonon Hall viscosity in atomically thin
crystals.
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Materials Science
Are we facing a reproducibility crises in materials synthesis? A systematic review of Turkevich AuNP synthesis and CVD MoS2 growth
Julia S. Correa, Leandro V. Silva, Nichollas G. G. Silva et al. (+3 more)
Reproducibility remains a major challenge in materials synthesis, particularly for nanomaterials whose properties are highly sensitive to experimental conditions. Here, we present a systematic review and meta-analysis evaluating the reproducibility of two widely used synthesis routes: the Turkevich method for gold nanoparticles (AuNPs) and the chemical vapor deposition (CVD) growth of MoS2. An adapted PRISMA-based protocol combined with a modified SPIDER framework was applied to assess methodological transparency, parameter reporting, and experimental consistency across the literature. More than 1,300 articles for each case study were retrieved from Scopus and Web of Science and systematically screened using structured checklists and a Python-based text classification
algorithm validated against independent human reviewers. Despite the extensive literature and the widespread perception of these methods as reproducible, only a small fraction of studies rigorously addressed synthesis reproducibility. Critical experimental parameters were frequently underreported, and statistical analyses were rarely included, limiting inter-laboratory comparability and reproducibility. These findings demonstrate the value of systematic reviews and meta-analyses as tools for identifying reproducibility gaps and guiding the development of more transparent and reliable synthesis protocols in materials science.
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All authors Julia S. Correa, Leandro V. Silva, Nichollas G. G. Silva, Cesar Raitz, Alex S. Lima, Daniel Grasseschi
Soft Condensed Matter
Density-driven reentrant polymer transitions via saturable bridging crowders
Monmee Phukan, Hitesh Garg and Satyavani Vemparala
Reentrant coil-globule-coil transitions, in which a
polymer collapses and then reexpands as a single parameter is varied, have been observed across diverse soft matter systems, yet the minimal ingredients required to produce them remain unclear. Using molecular dynamics simulations of coarse-grained
polymers interacting with a single species of attractive crowder, we show that crowder volume fraction $\phi_c$ alone is sufficient to drive a complete reentrant transition. At low $\phi_c$, crowders bridge distant monomers and drive cooperative collapse; at high $\phi_c$, saturation of monomer binding sites suppresses bridging connectivity and produces reentrant expansion. This density-driven transition is absent with purely repulsive crowders, which produce only monotonic compaction while preserving self-avoiding walk (SAW) chain statistics. In contrast, bridging breaks SAW universality: the rescaled size distributions no longer collapse onto a universal curve, and the conformational distributions trace the full coil-globule-coil trajectory as $\phi_c$ is varied. For charged
polymers with explicit counterions, electrostatics amplifies rather than suppresses reentrance: bridging crowders displace counterions from the chain, and upon saturation the unscreened backbone charges drive expansion well beyond the original chain size. Saturable
geometric bridging thus emerges as a minimal mechanism linking reentrant phenomena across neutral and charged
polymers in crowded environments.
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Strongly Correlated Electrons
Monopole Spin Density Wave States in Magnetic Weyl Semimetals
Xi Luo
The interplay between
topology and magnetism in Weyl semimetals has recently emerged as a fertile ground for novel
quantum phases. While monopole harmonic order parameters have been established for superconductivity and charge density waves in these systems, their
spin density wave counterparts remain unexplored. Here we introduce monopole
spin density wave (SDW) states arising from particle-hole pairing between nested
Fermi surfaces enclosing Weyl nodes of the same chirality. We demonstrate that the SDW order parameter inherits a nontrivial pairing Berry phase and is described by monopole harmonic functions that exhibit topologically protected nodal structures in the gap function. Through a concrete
lattice model, we show that helical and cycloidal SDW orders produce distinct signatures in band structures,
Fermi arc distributions, and surface
spin polarization patterns, which can be directly resolved by
spin- and angle-resolved photoemission spectroscopy. Remarkably, we find that the
quantum geometric tensor of the monopole pairing realizes ideal
quantum geometry in the weak-coupling limit, where
quantum distance fluctuations are entirely governed by Berry
curvature. Our results not only unify the understanding of monopole ordered states across pairing channels but also provide experimental avenues for distinguishing competing
magnetic orders in ReAlX (Re=rare earth elements, X=Si, Ge) materials and suggest potential applications in topological spintronics.
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Materials Science
SevenNet-Polar for MultiTask Prediction of Energy, Forces, Stress, and Born Effective Charges: Development and Application to ZrO$_2$, Li$_3$PO$_4$, and Perovskites
Anh Khoa Augustin Lu, Shungo Arai, Yutack Park et al. (+3 more)
Accurate prediction of the Born effective charge (BEC) tensor is crucial for modeling materials under electric fields but remains computationally expensive. To bridge this gap, we present SevenNet-Polar, an equivariant graph neural network framework based on the SevenNet architecture for fast and accurate BEC predictions. Our BEC-only predictors can achieve an RMSE as low as 0.0043 e on ZrO$_2$, Li$_3$PO$_4$, and perovskites, despite the presence of high-temperature (up to 2,000 K) and defect-laden training data. Our all-in-one multitask models for predicting energy, forces, stress, and BEC in ZrO$_2$ and Li$_3$PO$_4$ achieve high accuracy with an RMSE of 1.0 meV/atom for energy, 12 meV/angstrom for forces, 0.05 GPa for stress, and 0.0029 e for BEC. BEC accuracy is not degraded by multitask training. Scaling analysis reveals distinct exponents for diagonal and off-diagonal BEC components, both of which exhibit less favorable scaling than energy, force and stress errors. SevenNet-Polar generalizes robustly when tested on scenarios containing structural environments absent from the training set, such as along nudged elastic band (NEB) trajectories or grain boundaries in ZrO$_2$. Accelerated by FlashTP, SevenNet-Polar enables simulations containing up to 1.5 million atoms on multi-GPU supercomputers and up to approximately 15,000 atoms on a single consumer-grade GPU. This makes charge-aware molecular dynamics simulations under electric fields more accessible.
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All authors Anh Khoa Augustin Lu, Shungo Arai, Yutack Park, Seungwu Han, Tsuyoshi Miyazaki, Satoshi Watanabe
Superconductivity
$c$-axis strain tuning of superconductivity and symmetric elastoresistivity in CsV$_3$Sb$_5$
Xiaoran Yang, Yutong Li, Chunyi Li et al. (+5 more)
The kagome metal CsV$_{3}$Sb$_{5}$ hosts an intriguing interplay between charge-density-wave (CDW) order and superconductivity that is highly sensitive to
lattice distortions. However, determining the specific roles of the in-plane ($A_{1g,1}$) and out-of-plane ($A_{1g,2}$) symmetric strain channels has been hindered by their intrinsic mixing in conventional piezo-based experiments. Here, we combine in-plane uniaxial strain with direct $c$-axis compression to independently access and disentangle these
symmetry-resolved responses in CsV$_{3}$Sb$_{5}$. We reveal that $c$-axis compression drives a massive, linear enhancement of the superconducting transition temperature ($T_c$) alongside a suppression of $T_{\rm CDW}$. The tuning efficiency of this out-of-plane deformation acts with an opposite sign and far exceeds that of in-plane strain, demonstrating that $c$-axis
lattice control dictates the phase competition. Furthermore, by isolating the pure elastoresistivity coefficients, we find that the out-of-plane cross-coupling coefficient ($m_{13}$) is comparable in magnitude but opposite in sign to the in-plane response ($m_{11}+m_{12}$). Unlike the sharply peaked in-plane response, $m_{13}$ exhibits a distinct, order-parameter-like onset across the CDW transition. Our results establish that out-of-plane
lattice control plays a dominant role in tuning the intertwined states in CsV$_{3}$Sb$_{5}$ and provide a general pathway for resolving strain-coupled electronic responses in layered
quantum materials.
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All authors Xiaoran Yang, Yutong Li, Chunyi Li, Qi Tang, Jiawen Zhang, Yu Song, Huiqiu Yuan, Xingye Lu
Statistical Mechanics
The distribution of eccentricities in random regular graphs
Dor Lev-Ari, Ofer Biham and Eytan Katzav
We derive a closed-form analytical expression for the distribution of eccentricities (DoE) in random regular graphs (RRGs) that consist of $N$ nodes of degree $c$. The DoE is given by the tail distribution $P(E > \ell) \simeq 1 - \exp \left[ - \exp \left( - \frac{ e^{b \ell} - \mu }{\beta} \right) \right]$, where the distance $\ell$ takes integer values, $b = \ln (c-1)$ is the shape parameter, $\beta = \frac{c-2}{c} N$ is the scale parameter and $\mu = \frac{c-2}{c} N \ln N$ is the location parameter. By providing the full distribution rather than a single characteristic length scale, we present a detailed view of the large-scale structure. In spite of the fact that the degrees of all the nodes are the same, their eccentricities exhibit non-trivial variations. We derive a closed-form expression for the mean eccentricity, which is given by $\langle E \rangle \simeq \frac{\ln N}{\ln (c-1)} + \frac{\ln \ln N}{\ln (c-1)} - \frac{ \ln c - \ln (c-2) }{ \ln (c-1) } + \frac{1}{2}$. We calculate the mode of the DoE, which exhibits a staircase profile as a function of the network size. Interestingly, the mode is given by $E_{\rm mode} ={\rm Round} \left( \langle E \rangle \right)$, where ${\rm Round}( x )$ is the nearest integer to $x$. We also calculate the variance ${\rm Var}(E)$ and show that it exhibits oscillations as a function of the network size $N$. The results presented in this paper may serve as
benchmarks for algorithmic approaches to eccentricity calculations in large sparse networks. The eccentricities are important in practical applications such as broadcasting and global dissemination, where the network performance is determined by the longest delay times.
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Materials Science
Computing binary alloy phase diagrams with explicit configurational and vibrational entropy
Sarath Menon, Marvin Poul, Tilmann Hickel et al. (+2 more)
Phase stability in multicomponent solid solutions depends on configurational
entropy beyond the ideal mixing limit, but capturing it together with vibrational
entropy within the same atomistic framework remains challenging. Here, we extend non-
equilibrium thermodynamic integration to composition-dependent transformations through an alchemical interpolation of the interactions, combined with Monte Carlo identity exchange moves and molecular dynamics that sample the vibrational and non-ideal configurational
entropy along the integration path. We apply the framework to the Au-Cu binary
alloy using Atomic Cluster Expansion potentials trained on density functional theory data using the LDA, PBE, and r2SCAN functionals, and construct composition-temperature phase diagrams directly from atomistic free energies. We find that explicit configurational sampling lowers the AuCu order-disorder transition temperature predicted by the ACE potential trained on LDA data from approximately 810 K to 710 K, closer to the experimental value of 683 K, and substantially widens the stability range of the solid solution. At the same time, the much larger sensitivity to the exchange-correlation functional shows that this level of agreement should not be interpreted as general predictive accuracy. Non-ideal configurational
entropy must therefore be sampled explicitly, alongside a careful choice of functional, for a reliable atomistic description of binary phase diagrams.
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All authors Sarath Menon, Marvin Poul, Tilmann Hickel, Jörg Neugebauer, Ralf Drautz
Strongly Correlated Electrons
Emergence of a monopole phase in the $J_1{-}J_2$ Heisenberg model on the triangular lattice for small magnetic fields
Sasank Budaraju, Shi Feng, Josef Willsher et al. (+3 more)
We investigate the ground-state phase diagram of the $J_1{-}J_2$ Heisenberg model on the triangular
lattice under an external Zeeman field $H$ by using the variational Monte Carlo approach. We span a region with $0 \le J_2/J_1 \le 0.2$ and $0 \le H/J_1 \le 2$, to assess the fate of the (putative)
spin-
liquid phase that has been detected for $J_2/J_1=1/8$ at zero
magnetic field. Simple variational ansatze are proposed for a few candidate states, and their energetics are compared on large clusters to obtain the phase diagram. For $J_2/J_1 \lesssim 1/6$, a continuous transition from a gapless "Y” phase to a gapped "up-up-down” phase is obtained, as predicted by
spin-wave theory. Most importantly, around $J_2/J_1=1/8$, a condensate of monopoles (which are gapless gauge excitations of the
spin liquid at $H=0$) is stabilized in a significant region of the phase diagram, for small Zeeman fields. Here, a finite scalar chirality is present, while no transverse
magnetic order is detected. The stability of the monopole phase is confirmed by a field-theory approach that includes a self-consistent random-phase approximation of the low-lying
spin fluctuations. The boundary between the monopole and "Y” phases is also obtained with no free parameters.
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All authors Sasank Budaraju, Shi Feng, Josef Willsher, Johannes Knolle, Frank Pollmann, Federico Becca
Materials Science
Boson peak and medium-range elastic heterogeneity in calcium silicate hydrate probed by terahertz spectroscopy and low-temperature calorimetry
Xiangyu Li, Ying Chen, Jipeng Luo et al. (+9 more)
The
boson peak (BP), a universal vibrational anomaly of disordered solids, has been predicted but not systematically characterized in calcium silicate hydrate (C-S-H), the binding phase of hardened cement. Building on a preliminary terahertz survey, we characterize the BP across five Ca/Si ratios (0.5-1.7) using terahertz time-domain spectroscopy (THz-TDS) and low-temperature calorimetry, two probes of vibrational dynamics that complement the static picture of conventional structural methods. After Bruggeman correction for crystalline
impurities, both probes locate the BP near 1 THz; they agree on frequency but diverge in intensity. The terahertz integrated spectral weight and the calorimetric Cp/T3 peak both fall monotonically with Ca/Si, whereas the apparent terahertz peak height is maximal at Ca/Si = 1.0, where damping is low and oscillator strength still substantial. This decoupling marks a structural crossover between silicate-chain depolymerization and interlayer calcium filling. From the BP we obtain a medium-range dynamical correlation length of order 1 nm (0.3-2 nm) and a coherent-potential elastic-heterogeneity parameter that decreases from gamma = 0.98 to 0.48 as Ca/Si rises; the Debye-normalized BP frequency (nu_BP/nu_D = 0.15-0.17) places C-S-H within the range reported for silicate glasses. Because gamma governs the distribution of energy barriers for local structural rearrangements, it provides a quantitative, composition-resolved descriptor relevant to the intrinsic creep and thermal transport of C-S-H, linking nanoscale vibrational dynamics to the macroscopic durability of concrete. The dual-probe
boson-peak approach is transferable to other amorphous solids, including the supplementary cementitious materials of low-carbon cements.
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All authors Xiangyu Li, Ying Chen, Jipeng Luo, Ya Chen, Linhao Wang, Lidan Tian, Gan Ding, Zeyu Lu, Zhangli Hu, Biqin Dong, Yue Li, Zongjin Li
Materials Science
Tunable Magneto-Excitonic Coupling in Alloyed van der Waals Antiferromagnet
Maciej Smiertka, Oliwia Janikowska, Katarzyna Olkowska-Pucko et al. (+18 more)
The unique coupling between
magnetic order and photo-generated
excitons, electron-hole pairs bound by Coulomb interaction, in layered
magnetic semiconductors offers a powerful mechanism for controlling light-matter interactions. In the van der Waals antiferromagnet CrSBr, this coupling is exceptionally strong and manifests distinctly between two coexisting excitonic states: the localised, Frenkel-like XA
exciton and the more delocalised, Wannier-Mott-like XB
exciton, providing a unique playground for the optical control of magnetism. Here, we reveal how chlorine incorporation reshapes the magneto-optical interplay in CrSBr1-xClx by simultaneously modifying its electronic structure, excitonic properties, and
magnetic interactions. Combining magneto-optical spectroscopy up to 85 T with state-of-the-art quasiparticle self-consistent GW (QSGW) calculations on
alloy supercells, we show that Cl insertion progressively localises the excitonic wavefunctions and drives both states toward a more Frenkel-like regime. This
evolution is accompanied by a systematic reduction of the
magnetic-field-induced energy renormalisation, most prominently for the XB
exciton. Our work connects
exciton character directly to magneto-excitonic coupling. Furthermore, it establishes compositional alloying as an effective strategy for engineering the coupling between
magnetic and optical properties in van der Waals
magnetic semiconductors.
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All authors Maciej Smiertka, Oliwia Janikowska, Katarzyna Olkowska-Pucko, Grzegorz Krasucki, Katarzyna Posmyk, Paulina Peksa, Alessandro Surrente, Dimitar Pashov, Kseniia Mosina, Zdenek Sofer, Mark van Schilfgaarde, Adam Babinski, Maciej R. Molas, Gabriela Komorowska, Esteban Zamora-Amo, Andres Castellanos-Gomez, Federico Mompean, Mar Garcia-Hernandez, Michal Baranowski, Swagata Acharya, Paulina Plochocka
Soft Condensed Matter
Amoeboid swimming of active vesicles
Reiner Kree and Annette Zippelius
We investigate the shape dynamics and migration of weakly deflated active vesicles driven by processes acting either directly in the membrane or transmitted by the cytoskeleton. For a force-free vesicle, local membrane incompressibility suppresses rigid-body translation, so that migration arises from time-dependent shape deformations. Assuming small excess area enables a systematic analysis of the coupled deformation and migration dynamics in free space, i.e. in the absence of substrate adhesion or confinement. Depending on the strength and frequency of the activity, the vesicle exhibits several dynamical regimes, including synchronized oscillations, quasiperiodic shape changes, transitions between non-propelling and propelling states, and intermittent motion.
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Materials Science
Direct observation of anisotropic exciton dispersion in the 2D semiconductor CrSBr
Yiwen Song, Peiyi He, Weizhe Zhang et al. (+7 more)
We report momentum-resolved measurements of
exciton dispersion in multilayer CrSBr using defocus-engineered electron energy-loss spectroscopy, supported by first-principles calculations. A pronounced in-plane anisotropy is observed, with the
exciton exhibiting a linear dispersion along $\Gamma$Y within $\lvert \boldsymbol{q} \rvert$ < 0.007 Å$^{-1}$, while remaining nearly dispersionless along $\Gamma$X. The slope reaches 7.02 eV Å, among the largest reported in low-dimensional systems. The calculations reproduce the experimentally observed linear dispersion, confirming its intrinsic origin. We attribute the anisotropic dispersion to the long-range electron–hole exchange interaction, enhanced by strong out-of-plane confinement and governed by the directional selection rules of the transition dipole moment. Comparative measurements across the
magnetic phase transition from the paramagnetic to the A-type
antiferromagnetic state show that the dispersion remains essentially unchanged, indicating negligible coupling between
exciton propagation and
magnetic order. These results establish CrSBr as a model system for investigating anisotropic
exciton dynamics in low-
symmetry layered
semiconductors.
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All authors Yiwen Song, Peiyi He, Weizhe Zhang, Wenyuan Ouyang, Wenjing Liu, Jinlong Du, Zuxin Chen, Jiuyu Sun, Peng Gao, Yu Ye
Superconductivity
Imaging and characterization of spontaneous vortices in a proximity-induced superconductor
Iku Nakaaki, Kotaro Taki, Mio Nomura et al. (+11 more)
Observation of spontaneous
symmetry breaking is crucial for understanding continuous second-order phase transitions from disordered to ordered states, which often leads to the formation of topological defects. In
superconductors, such topological defects manifest as quantized
vortices. However, the formation and observation of spontaneous
vortices in a uniform
superconductor are challenging because extremely rapid cooling (>108 K/s) is generally required for that purpose. Here we conducted scanning superconducting
quantum interference device microscope (SSM) measurements on an MgB2-based proximity-induced
superconductor, an intrinsically inhomogeneous system. In this system, individual superconducting domains will reach internal
equilibrium independently during cooling and choose their own phase before the global phase coherence is established via the long-range proximity coupling. The SSM measurements demonstrate that
vortices are nucleated spontaneously even at a relatively slow cooling rate (~0.2 K/s). We also find that the
vortices with different polarities, sizes, and shapes appear stochastically under near-zero-field conditions. The geometry of the spontaneous
vortices is more extended than that of the field-induced Abrikosov
vortices.
Magnetic field profile analysis based on the London model elucidates that penetration depths of the extended
vortices are anomalously large, exceeding several micrometers. This unusual morphology of the spontaneous
vortices most likely imprints the information that is frozen at the moment of
vortex formation. Our findings not only provide insights into the local phase differences present in the early stage of the phase transition in this proximity-induced superconducting system, but they also shed insights into the structure, formation, and stabilization of topological defects in highly disordered and inhomogeneous superconducting systems.
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All authors Iku Nakaaki, Kotaro Taki, Mio Nomura, Haruna Ishimaru, Minagi Yono, Jun Chen, Hiroyo Segawa, Akiko Nakamura, Taku Moronaga, Minoru Tachiki, Shuuichi Ooi, Shunichi Arisawa, Tsutomu Nojima, Takashi Uchino
Strongly Correlated Electrons · Cross-listed from quant-ph
Electrons Hopping across a Molecular Network: Spectra and Symmetries
Ludwig Schulz, Max Best and Carsten Henkel
We investigate interacting spinless electrons on finite molecular ring networks described by a tight-binding Hubbard
Hamiltonian. The interplay between
lattice geometry, Coulomb interactions and discrete
symmetries is analysed for rings with $L=3,4,5,6$ nodes, filled with one, two or three electrons. Special
attention is devoted to the role of the network
symmetries in determining the structure of the many-body spectrum and the Mulliken classification of the eigenstates. Using group-theoretical methods, we examine the
evolution of the spectra in the presence of an external
magnetic flux. The Zeeman effect lifts degeneracies and results in combination with the Coulomb interaction to avoided crossings in
symmetry sectors. We identify a qualitatively distinction between systems with an even and odd number of particles. At half-filling, particle-hole
symmetry (duality) protects selected
symmetry sectors against Zeeman splitting.
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Superconductivity
Spin-fluctuation-mediated unconventional $d_{xy}$-wave superconductivity in ThFeAsN from first-principles
Guang-Yu Guo, Jau-Wen Liu and Mitsuaki Kawamura
Superconducting (SC) pairing mechanism, origin of high $T_c$ and
symmetry of SC order parameter in Fe-based
superconductors are among the important unsolved problems in condensed matter and materials physics. We study the SC properties of ThFeAsN, a Fe-based high $T_c$
superconductor, by ab initio superconducting density functional theory calculations with electron-
phonon coupling, screened static and dynamic electron-electron Coulomb repulsion and
spin fluctuation (SF) mediated pair-interaction fully taken into account. Our calculations reveal that ThFeAsN is a SF-mediated multiband
superconductor with the calculated $T_c$ of 22.4 K and the $d_{xy}$-wave SC order parameter with different signs on different
Fermi surface sheets, in consistent with experiments. We also present distinct SC properties such as quasiparticle density of states and ultrasonic attenuation coefficient which can be immediately verified by experiments.
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Statistical Mechanics · Cross-listed from quant-ph
Tuning the universality class of a quantum process by Trotterization
Robin Prampain dit Boulan, Jerom Jebai and Hendrik Weimer
We numerically analyze a discretized version of the
quantum contact process, a non-
equilibrium model having a competition between a coherent infection process and a dissipative recovery process. Previously, the continuous-time version has been discussed to have a phase transition in a novel
quantum universality class, while experimental investigations of a related process have pointed towards the transition being in the classical directed percolation class. We demonstrate that these differences stem from details of the discretization of the process and construct a systematic way to continuously interpolate between these results. Finally, we provide evidence that the modification of the universality class is due to destructive interference effects, showing a clear
quantum-mechanical origin.
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Soft Condensed Matter
Numerical and experimental framework for bending elasticity of highly flexible slender structures
Shunsuke Nomura, Satsuki Shibuya, Isamu Hashiguchi et al. (+2 more)
Slender structures are highly flexible, spanning several orders of magnitude in length scale. Their deformation depends on the slenderness of their cross sections, highlighting that the elasticity and geometry of structures are intrinsically coupled. The deformation of the cross-section becomes significant, particularly when tubes and pipes are subjected to bending, known as the Brazier instability. Although the bending performance of slender structures is quantified experimentally using a canonical three-point bending test, their numerical counterparts remain under-explored because complex contact mechanics must be implemented in simulations. In this study, we develop a computational framework to simulate experimental three-point bending tests using a hybrid material point method (hybrid-MPM) approach, which integrates Lagrangian finite element and Eulerian finite difference frameworks. We adapt our framework to elastic tubes and tape springs as canonical examples that exhibit characteristic bending deformation in which the cross-sectional and lengthwise bending are coupled. The predictions of numerical simulations are validated against desktop experiments and classical theory. The excellent agreement between the simulation and the experiments implies that the hybrid-MPM framework provides a robust computational framework for predicting the large deformation of structures involving complex contact, such as soft
robots and deployable structures.
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All authors Shunsuke Nomura, Satsuki Shibuya, Isamu Hashiguchi, Ryuichi Tarumi, Tomohiko G. Sano
Materials Science
Second-Order Optical Nonlinearity of AlScN Films Grown By Molecular Beam Epitaxy
Joongwon Lee, Thai-Son Nguyen, Len van Deurzen et al. (+8 more)
Alloys of AlN have rapidly emerged as a material platform for nonlinear optics. In this paper, we measure the second-order optical nonlinearity of AlScN films grown directly on nitrided c-plane sapphire by molecular beam epitaxy. This direct growth approach, which bypasses a thick AlN buffer layer, allows us to isolate the true nonlinear response of the AlScN film. Our results show a large enhancement of d31, but a suppression of d33 in AlScN films compared to AlN. We observe that d31 can be as high as 4.92 pm/V , which is 60 times larger than that of AlN. The development of AlScN-based photonic devices can enable energy-efficient nonlinear optical operations that can be epitaxially integrated with electronic and photonic devices based on Si, GaN and AlN.
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All authors Joongwon Lee, Thai-Son Nguyen, Len van Deurzen, Debaditya Bhattacharya, Chandrashekhar Savant, Siddhartha Ghosh, Patrick Shea, Carl Bernard, Huili Grace Xing, Debdeep Jena, Farhan Rana
Other Condensed Matter
A Modern Multimodal Assistant on a 6 GB 2011 GPU: Stage-Validated, All-GPU CUDA Inference for Fermi
A. C. Opus and J. Q. Lu
A companion study ran a 35B mixture-of-experts model on a 2011 NVIDIA Tesla C2075 (
Fermi, sm_20, 6GB) as a GPU-prefill/CPU-decode hybrid, because the 4-bit model did not fit in device
memory (arXiv:2606.24031). This report keeps the hardware and asks what a model that fits can do: we deploy MiniCPM-V-4.6, a modern
multimodal assistant pairing a SigLIP2
vision encoder and window-
attention merger (16x visual
token compression) with a compact hybrid gated-delta-net backbone, entirely on the GPU. Three results. (i) An all-GPU engine built on measured foundations: projections that dequantize 8-bit weights once and call the vendor SGEMM still in the last
Fermi toolchain (64% of FP32 peak; our best hand-written GEMM hit 37%, wrongly called the ceiling); a chunked delta-rule rewrite of the recurrent layers, 2.8x faster than the sequential scan once attribution exposed one bad kernel; and a measured negative: 4-bit weights make decode slower than 8-bit here, since
Fermi issues nibble-unpacking shifts at half rate. (ii) The
vision side is a port with a proof obligation: we translate tower, merger, and projector to sm_20 CUDA, validating every stage against a locally generated reference forward (full tower 1.4e-5). One failure, position-
embedding bucketization differing on exact rational ties, generalizes to a rule: float tie-breaking in index arithmetic is implementation-defined; call the reference operator, do not reimplement it. (iii) Long context exposes an O(N^2) wall short
benchmarks hide: prefill falls from 114 tok/s at 2k
tokens to 21 at 10k in a naive
attention kernel; per-head vendor-GEMM calls writing into the existing score buffer (zero extra
memory) restore a flat profile (408 at 2k, 361 at 10k; 17x), verified by exact needle
retrieval from 60% depth. The same rewrite cuts image encoding 6x, to 0.93s. The system answers an image question end-to-end in 1.7s.
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