Other Condensed Matter
Integer-Graded Reciprocal Skin Effect from Internal Rotation
Kin Hung Fung and C. T. Chan
A prominent class of reciprocal non-Hermitian skin effects has a $\Z_{2}$ topological classification, characterized by a parity invariant protected by reciprocity. We show that conserved internal rotation refines this classification into an unbounded integer-graded hierarchy. Every angular momentum channel is an exactly solvable asymmetric chain with its own integer point-gap winding, while conjugate channels accumulate at opposite edges so that reciprocity is preserved globally. For conserved channels, the classification contains one integer per conjugate pair, with the number of independent integers determined by the internal multiplet. Half-integer
spin realizes the
symplectic class AII$^{\dagger}$, whose $\Z_{2}$ index is recovered as the parity of the grading. Conjugate-channel mixing destroys the grading and leaves a critical, scale-free skin effect. A cyclic three-site
lattice and a passive array of lossy resonators provide minimal realizations.
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Materials Science
Performance of Tkatchenko-Scheffler Dispersion Method with Updated van der Waals Radii: Importance for Alkali-Containing Systems
Aaron M. Schankler, Ruyi Song, Sampreeti Bhattacharya et al. (+5 more)
The Tkatchenko-Scheffler (TS) pairwise method to calculate dispersion interactions is a widely used approach to incorporate missing long-range van der Waals contributions in semilocal and hybrid density functional calculations. Despite numerous refinements of the approach to include many-body terms, the original formulation still remains highly relevant as an efficient and robust method, especially for organic and/or insulating materials. In 2018, Fedorov et al. reported updated van der Waals radii to the seminal work published in 2009. The present work examines the accuracy of the TS method with updated van der Waals radii (abbreviated as TS_2018), coupled with the semilocal Perdew-Burke-Ernzerhof density functional, for structural predictions of semiconducting and insulating materials in comparison to the non-local many-body dispersion method and the original TS method (TS_2009). Special
attention is paid to materials containing alkali elements, for which the TS_2009 method exhibits a large overbinding, associated with potentially large errors in predicted atomic structures. We also consider a more narrow reformulation (TS_alkali) where only the the alkali atoms are corrected, so the method remains otherwise compatible with TS_2009. The binding energy curves of five alkali dimers are used to assess the TS_2009 and the TS_2018 methods in comparison to the random phase approximation. Using 45 inorganic solid compounds with available experimental reference data, as well as three widely studied, Cs-containing halide perovskites, CsPb$X_3$ ($X$ = Cl, Br, I), we then examine the performance of the TS_2018 and TS_alkali approaches compared to TS_2009 and the beyond-pairwise, nonlocal many-body dispersion method; the latter found to give good results as well.
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All authors Aaron M. Schankler, Ruyi Song, Sampreeti Bhattacharya, Ela Lucas, Lee Hampton III, Alexandre Tkatchenko, Yosuke Kanai, Volker Blum
Disordered Systems and Neural Networks
Griffiths phase in clique percolation in random geometric graphs
Vasilii Tiselko, Olga Valba and Alexander Gorsky
In this study, we discuss the clique percolation in the ensembles of random
geometric graphs with different kernels that quantify the geometrical constraints. For the sharp cut-off we find the wide Griffiths phase of extended criticality with the power-law behavior. One boundary of the Griffiths phase is the generalization of a percolation critical point for the ER ensemble when the percolation within the large but finite cluster emerges. The second boundary corresponds to the point in the parameter space when the percolation in the entire clustered system becomes available. For the power-law kernel, richer behavior with a clique-size-dependent boundary between the effective ER and
geometric regimes has been identified. The Griffiths phase in this case exists as well. Finally, the pattern with the exponential kernel has been analyzed. We briefly discuss the possible applications of our findings.
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Materials Science · Cross-listed from quant-ph
Surface adsorbates suppress low-frequency noise for shallow nitrogen-vacancy centers
Zhiyang Yuan, David A. Fehr, Kalliope Zervas et al. (+5 more)
Shallow nitrogen-vacancy (NV) centers in diamond are promising nanoscale
quantum sensors, yet their coherence is strongly limited by surface-induced noise. Surface adsorbates are widely believed to be a major source of decoherence. Here, we test this assumption by characterizing shallow single NV centers under ultrahigh
vacuum (UHV) conditions, where the diamond surface is kept free of adsorbates, and comparing their behavior to ambient conditions. Surprisingly, we observe a ~4x reduction in the Hahn echo coherence time T2 in UHV. By combining Hahn echo measurements in the single-
quantum (SQ) and double-
quantum (DQ) bases, we separate contributions from different noise sources and find that both electric and
magnetic noise are enhanced in UHV. In contrast, T1 measurements reveal an increased DQ T1 in UHV, indicating suppressed electric field noise in the ~100 MHz frequency regime. These results point to a modification of the surface noise spectrum upon adsorbate removal, with different frequency regimes arising from distinct microscopic mechanisms. Specifically, we find that the low frequency noise is consistent with increased surface charge in UHV that can be compensated by surface adsorbates in ambient conditions. Our findings highlight a complex and previously underappreciated role of surface adsorbates in shaping the noise environment of shallow NV centers, with important implications for nanoscale
quantum sensing.
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All authors Zhiyang Yuan, David A. Fehr, Kalliope Zervas, Sorawis Sangtawesin, Lila V. H. Rodgers, Patryk Gumann, Michael E. Flatte, Nathalie P. de Leon
Materials Science · Cross-listed from cs.AI
PolymerGPT: Multi-property Optimization with a Decoder-Based GPT Model for Generative Polymer Design
Charlie Pyle, Adarsh Gadari, C. Adrian Figg et al. (+3 more)
Polymer property prediction and inverse generative design targeting desired properties are two crucial tasks in machine learning-assisted
polymer design. While the former has received considerable
attention, there have been limited methods developed for the latter. Existing methods focus on single-property optimization in the generative process, whereas accurate prediction of macroscopic material behavior requires simultaneous control of multiple physical properties. In this paper, we provide a transformative framework for direct optimization of a large collection of
polymer properties. We propose PolymerGPT, a decoder-based GPT model that incorporates up to 37 commonly used
polymer properties into the generative process via learned conditioning prefixes. It also supports a scaffold condition that specifies a desired scaffold for predicted structures. Our experimental results demonstrate that PolymerGPT achieves exceptional performance for unconditional and conditional generation while maintaining high validity, uniqueness, and novelty. Conditioning on five key properties yields generated structures whose predicted values closely match all target properties simultaneously.
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All authors Charlie Pyle, Adarsh Gadari, C. Adrian Figg, Zhenquan Jia, Yaohang Li, Chunjiang Zhu
Mesoscale and Nanoscale Physics
Bulk-Boundary Correspondence in Semi-Infinite Chains from Sublattice Zeros
Ilya Iakoub, Nicolas Levasseur, Kylian Lionnet et al. (+1 more)
We provide an alternative derivation of the bulk-boundary correspondence for semi-infinite chains. To describe edge states, we analytically continue the usual Bloch
Hamiltonian to complex wave vectors $k$. To start, we note that the zeros of a Bloch wavefunction are related to edge states, at least in systems with nearest-neighbour hoppings. We show that an analytically continued Bloch
Hamiltonian with
chiral symmetry has exceptional points, where two different states coalesce. These special points are related to the adiabatic protection of edge states. We derive a winding number that counts the number of topological edge states protected by
chiral symmetry.
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All authors Ilya Iakoub, Nicolas Levasseur, Kylian Lionnet, Richard MacKenzie
Strongly Correlated Electrons
Quantum geometry and RKKY in flat bands
Chang-geun Oh, Makoto Shimizu, Youichi Yanase et al. (+1 more)
Flat conduction bands quench the group velocity and thus challenge conventional, dispersion-driven pictures of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, where localized moments are coupled via an effective exchange mediated by conduction electrons. Here we show that RKKY interactions in the flat-band limit are not extinguished by the vanishing group velocity but are instead mediated by the
quantum geometry of Bloch states. Starting from a microscopic RKKY derivation, we demonstrate that the Brillouin-zone-averaged
quantum metric controls the long-wavelength structure of the static susceptibility, thereby determining the
magnetic correlation length and the
spin stiffness. As a result, the finite spatial spread of Wannier functions provides an effective long-range coupling channel even when single-particle dispersion is absent. Furthermore, we establish the general principle that the ordering temperature is governed by the
quantum metric in finite and low-dimensional samples, effectively circumventing the thermodynamic-limit constraint of the Mermin-Wagner
theorem. Specifically, our theoretical investigation reveals that increasing the
quantum metric enhances
magnetic rigidity and leads to a corresponding rise in the critical temperature within finite-sized systems.
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All authors Chang-geun Oh, Makoto Shimizu, Youichi Yanase, Shuichi Murakami
Mesoscale and Nanoscale Physics
Microwave Response of the Superconducting Diode Effect in Proximitized Bilayer Graphene Interferometers
Shili Yan, Rubén Seoane Souto, Yi Luo et al. (+7 more)
Microwave irradiation has emerged as a promising means to tune the superconducting diode effect (SDE) in Josephson junction devices. Previous experimental studies have mainly focused on the adiabatic-driving regime, in which the diode efficiency increases monotonically with microwave power and can approach the ideal value of unity. Beyond this regime, however, the microwave response of the SDE remains largely unexplored experimentally. In this work, we investigate the microwave response of the SDE in
bilayer-
graphene-based superconducting
quantum interference devices (SQUIDs) under a broad range of driving frequencies. We show that increasing the driving frequency changes the response characteristics of the diode efficiency to microwave power–the dependence of the diode efficiency evolves from monotonic enhancement with increasing microwave power in the adiabatic regime to non-monotonic behavior beyond this regime, and ultimately to sign-reversal as well oscillatory characteristics at sufficiently high frequencies. We find that these experimentally observed frequency-dependent power response characteristics of the diode efficiency can be qualitatively captured by simulations based on the resistively shunted junction model using the device current-phase relations extracted from the experiments. These results establish SQUIDs made from
bilayer graphene as a versatile platform for studying dynamic properties of superconducting junction devices.
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All authors Shili Yan, Rubén Seoane Souto, Yi Luo, Jeroen Danon, Haitian Su, Junze Zhang, Han Gao, Xingjun Wu, Ji-Yin Wang, H. Q. Xu
Strongly Correlated Electrons
All-Electric Topological Phase Transitions in Proximity-Coupled Bilayer MnBi2Te4 Heterostructures
Basavaraja G and Mukul Kabir
The intrinsic
magnetic topological
insulator MnBi2Te4, in the two-dimensional limit, hosts thickness dependent
axion and
quantum anomalous Hal (QAH) insulating states governed by
antiferromagnetic interlayer coupling. However, controlled interconversion between these phases typically requires extreme external
magnetic fields exceeding 9 T, limiting practical tunability. Using complementary first-principles calculations and effective
Hamiltonian modeling, we demonstrate a field-free, reversible mechanism to engineer topological phase transitions by exploiting
magnetic proximity at the interfaces with a
ferromagnetic insulator. Gate-tunable
magnetic anisotropy within the
ferromagnetic insulator dynamically modulates the proximity-induced exchange bias, enabling all-electric switching of interlayer coupling and band
topology in ultrathin MnBi2Te4. Crucially, long-range Heisenberg Monte Carlo simulations reveal that the
magnetic ordering temperature of the encapculated MnBi2Te4 film is dramatically elevated. By eliminating the high-field requirement and simultaneously improving thermal stability, this gate-tunable paradigm solves a critical bottleneck in topological physics and offers a viable route toward scalable, high-temperature topological electronics.
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Superconductivity
Electron-like high-temperature superconductivity induced by compressive strain in La2PrNi2O7 thin films
Zhiwei Wang, Zhengjie Wang, Huiyu Wang et al. (+8 more)
The realization of high-temperature superconductivity in
bilayer nickelates under epitaxial compressive strain is widely interpreted as mimicking the effects of high hydrostatic pressure. To test the equivalence of these mechanisms, we investigated a comprehensive strain continuum ranging from compressive (-2.14%) to tensile (+0.91%). Crucially, via ozone-assisted atomic-layer epitaxy, we realized high-temperature superconductivity in as-grown La2PrNi2O7 films on NdAlO3 substrates, which induce the most extreme compressive strain in this material system. Under extreme compression (-2.14%), these films exhibit a Tc_onset of 60 K, zero resistance at 33 K, and a diamagnetic response at 20 K, with magnetotransport measurements confirming a quasi-two-dimensional superconducting nature. Comparing our phase diagram with reported data reveals distinct
lattice responses: unlike in pressurized
crystals, the superconducting window in epitaxial films diverges significantly in the out-of-plane parameter c (or c/ap ratio) but remains consistent with the bulk regarding the in-plane parameter ap. Crucially, while superconductivity in both systems emerges from the suppression of
spin-density waves (SDW),
Hall measurements reveal a fundamental electronic dichotomy: optimal superconducting films are intrinsically electron-like (exhibiting a negative
Hall coefficient), in stark contrast to the hole-like nature (positive
Hall coefficient) of high-pressure bulk
crystals and non-superconducting tensile films. Ultimately, both tuning strategies effectively modulate the underlying correlation landscape - the true driver of superconductivity - transcending the constraints of specific
Fermi surface
topologies. This work establishes a macroscopic platform for probing the multi-orbital physics of nickelates, offering a new dimension for investigating high-temperature superconductivity.
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All authors Zhiwei Wang, Zhengjie Wang, Huiyu Wang, Mingyi Zhu, Mengzu Shi, Zongyao Huang, Houpu Li, Shoucong Ning, Jing Tao, Tao Wu, Xianhui Chen
Statistical Mechanics
Algorithmic overlaps in the Baxter-Wu model: cluster dynamics under Novotny-Evertz updates
Ian Pilé and Lev Shchur
We study the spatial overlap of successive
spin configurations generated by Markov chain Monte Carlo simulations of the Baxter-Wu model. Using the Novotny-Evertz sublattice-freezing single-cluster update, we track the mean and variance of the algorithmic overlap across the critical region. We show that, even in this three-
spin model, the overlap acts as an algorithmic observable that follows the thermodynamics of the transition: the single-cluster overlap mean behaves like an order parameter, dropping from a finite ordered-phase plateau toward zero across $T_c$. The overlap does not diverge at criticality, instead it remains finite and its finite-size value decays as a clean power law, $U_2(T_c)\sim L^{-\psi}$, over eleven sizes with an exponent $\psi{=}0.378(4)$ smaller than the value $\approx0.42$ found for the Ising and Potts models under standard Fortuin-Kasteleyn cluster dynamics, indicating that it reflects the Novotny-Evertz sublattice-freezing dynamics rather than any static property of the model.
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Materials Science
Why Ammoniated Lithium Borohydrides Liquefy and Resolidify?
Qian Wang, Zixin Xu, Ryuhei Sato et al. (+7 more)
Ammonia (NH$_3$) absorption drives LiBH$_4\cdot x$NH$_3$ through a re-entrant “solid–
liquid–solid” transition: LiBH$_4\cdot$NH$_3$ is a well-defined solid ammoniate, compositions near LiBH$_4\cdot 2$NH$_3$ are
liquid-like or partially liquefied, whereas LiBH$_4\cdot 3$NH$_3$ returns to a more rigid non-
liquid ammoniate state. However, the microscopic origin of this unintuitive response remains a long-lasting mystery. Here, we uncover its mechanism. Cross-database analysis identifies borohydrides as a particularly state-diverse and composition-responsive material family. Structure prediction and ab initio molecular simulations reveal that increasing NH$_3$ loading increases the direct Li–N coordination number while progressively decreasing BH$_4^-$-associated contacts in the local Li environment. Near $x \approx 2$, these contributions are most balanced among the simulated compositions, and the sampled Li–N/N$\cdots$B coordination landscape is broadest. Further ammoniation produces Li–N-dominant coordination and slower BH$_4^-$/NH$_3$ contact renewal, accompanying recovery of a more rigid ammoniate state. Pressure–composition isotherm, $^1$H and $^{11}$B
nuclear magnetic resonance, and Raman measurements support this non-monotonic state
evolution and associated BH$_4^-$/NH$_3$ reorganization. These findings transform ammonia-induced liquefaction from an empirical phase anomaly into a competition between native-network disruption, mixed-coordination frustration, and ligand-built network reconstruction, providing a framework for chemically switching between transport-favouring fluidity and stability-favouring
rigidity in hydrogen-rich materials.
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All authors Qian Wang, Zixin Xu, Ryuhei Sato, Yiming Lu, Hiroki Miyaoka, Takayuki Ichikawa, Eric Jianfeng Cheng, Shin-ichi Orimo, Fangqin Guo, Hao Li
Superconductivity
$d$-spacing distributions as a probe of nematoelastic response in iron-based superconductors
Wenting Zhang, Ruixian Liu, Tingjun Zhang et al. (+14 more)
Electronic nematicity in iron-based
superconductors (FeSCs) couples bilinearly to orthorhombic strain, allowing nematic correlations to appear in the
lattice response. Here we use
neutron Larmor diffraction to measure the temperature-dependent distribution of relative $d$ spacings in electron-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, hole-doped Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$, FeSe, and Fe$_{1.07}$Te. In Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$
crystals without intentionally applied uniaxial stress, the in-plane distribution width, $\varepsilon_{\rm FWHM}$, increases on cooling in the tetragonal phase and can be described phenomenologically by a Curie–Weiss-like form. The fitted scale $T^*$ decreases with Co doping and evolves similarly to the nematic phase diagram inferred from elastoresistance, although the two experiments probe different response functions. Related broadening in Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$ and FeSe supports extending this interpretation beyond electron-doped BaFe$_2$As$_2$. By contrast, Fe$_{1.07}$Te shows no extended Curie–Weiss-like regime without applied stress, whereas uniaxial pressure produces a strongly anisotropic broadening that can contain contributions from both the field-biased
lattice response and inhomogeneous loading. A mean-field model with bilinear nematoelastic coupling and spatially varying
symmetry-breaking stress explains the Curie–Weiss-like broadening in terms of the renormalized orthorhombic compliance.
Neutron Larmor diffraction therefore provides a bulk-sensitive probe of nematic-related
lattice broadening that complements electronic and elastic measurements.
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All authors Wenting Zhang, Ruixian Liu, Tingjun Zhang, Weiliang Yao, Xüe Fu, Hanqing Xie, Ziye Mo, Ting Guo, Kuo-Feng Tseng, Thomas Keller, Jitae T. Park, Fankang Li, Masaaki Matsuda, Avishek Maity, Long Tian, Pengcheng Dai, Xingye Lu
Mesoscale and Nanoscale Physics · Cross-listed from physics.app-ph
Active Passivation Tunes Hotspot Locations in GaN Transistors with In Situ Thermal Mechanical Visualization
Yicheng Wei, Sihang Liu, Zimu Jiang et al. (+6 more)
Efficient thermal dissipation has become critical in emerging electronic devices. However, most existing studies have primarily focused on engineering heat dissipation pathways, largely overlooking the intrinsic behavior of the heat source itself. We demonstrate an active passivation technology that proactively tunes hotspot locations in GaN transistors. By adjusting the active passivation layer length, the hotspot is shifted from the gate edge to the drain-side AP edge, establishing a clear one-to-one spatial correlation. In-situ thermal-mechanical visualization via micro-Raman thermography, combined with multi-physics electro-thermal-mechanical simulations, directly captures the spatial redistribution of both temperature and thermal stress profiles. Electrical analysis confirms that this hotspot migration is driven by the spatial shift of the peak electric field and localized Joule heating. This proactive heat-source tuning strategy provides critical design guidelines for power electronics.
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All authors Yicheng Wei, Sihang Liu, Zimu Jiang, jinquan Zhang, Zifeng Huang, Han Yang, Yang He, Jin Wei, Zhe Cheng
Strongly Correlated Electrons
Pressure-induced self-doping and Fermi surface reconstruction in UAs2
Zhenchao Wu, Yingying Cao and Yi-feng Yang
Superconductivity has recently been reported in the heavy-
fermion compound UAs2 under pressure, with the highest Tc among uranium-based correlated 5f-electron
superconductors. To elucidate its microscopic origin, we investigate its electronic structure using density functional theory combined with dynamical mean-field theory (DFT+DMFT). At ambient pressure, our calculations reproduce the characteristic Kondo-
lattice electronic structure, with flat hybridization bands near the
Fermi energy around the {\Gamma} and M points, in good agreement with angle-resolved photoemission spectroscopy (ARPES). Under pressure, we find a systematic transfer of electrons from the more localized 5f5/2 orbitals to the more itinerant 5f7/2 orbitals, while the total U-5f occupancy remains nearly unchanged. This orbital-selective charge redistribution constitutes a pressure-induced self-doping effect that drives the 5f5/2 electrons from a localized Kondo regime toward a mixed-valence regime with enhanced charge fluctuations, leading to a dramatic reconstruction of the low-energy electronic structure. Remarkably, superconductivity emerges in the pressure range where the
Fermi surface consists of two disconnected sheets with enhanced nesting, but disappears when they bend and merge into a corrugated three-dimensional cylinder. Our results provide an electronic-structure basis for understanding superconductivity in UAs2 and suggest that
Fermi-surface nesting and charge fluctuations may contribute to the enhanced superconducting Tc, pointing to a possible distinction from conventional heavy-
fermion superconductors.
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Materials Science
Twist-induced magnetic topological phase transition in stacked altermagnetic CrO
Zi-Hao Ding, Ze-Feng Gao, Xiang-Hua Kong et al. (+2 more)
Interlayer twisting offers a
geometric route to controlling electronic states, but whether it can simultaneously reconstruct
magnetic symmetry and band
topology remains unclear. Here, based on
symmetry analysis and first-principles calculations, we show that commensurate twisting drives
magnetic topological phase transitions in stacked
bilayer CrO. In particular, it transforms an
antiferromagnetic Dirac semimetal into either a $d$-wave altermagnetic bipolarized Weyl semimetal or an unconventional compensated
magnetic Weyl semimetal. A key result is that the Weyl points in the $d$-wave altermagnetic phase lie at generic $k$ points in the Brillouin zone and are protected by the
spin symmetry $\left\{ C_2 T||C_{2z} T\right\}$. This sharply contrasts with conventional two-dimensional Weyl semimetals, where Weyl points are typically protected by mirror or rotational
symmetries and thus pinned to high-
symmetry lines. We further show that commensurate twisting preserves the
spin symmetry $\left\{ C_2 T||C_{2z} T\right\}$, making the Weyl phase a robust consequence of twisting rather than a fine-tuned feature of a specific angle. Our work establishes a
symmetry-based route to engineering
magnetic topological phases in twisted two-dimensional materials.
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All authors Zi-Hao Ding, Ze-Feng Gao, Xiang-Hua Kong, Peng-Jie Guo, Zhong-Yi Lu
Mesoscale and Nanoscale Physics
Suppressed plasmon excitations, enhanced damping and static screening in Kek-Y strained $\alpha-\mathcal{T}_3$ model
Jean Marseille, Teresa Lee, Andrii Iurov et al. (+3 more)
We performed a rigorous theoretical and numerical investigation into the polarization function, plasmon excitations, and plasmon damping in the Kek-$\alpha$ model, a two-dimensional material combining the key features of the $\alpha-\mathcal{T}_3$
lattice and Kekule-distorted
graphene. Unlike conventional Kek-Y
graphene, the Kekule modulation in the Kek-$\alpha$ model affects only one of the two sublattices, giving rise to a fundamentally new model with unusual electronic properties. The low-energy spectrum consists of two degenerate flat bands and two inequivalent Dirac cones with different
Fermi velocities, referred to as the fast and slow cones. The particle-hole continuum responsible for Landau damping exhibits two distinct branches associated with transitions involving these Dirac cones. An additional particle-hole mode originates from electron transitions associated with the fast Dirac cone, appearing above the main diagonal. As the parameter $\alpha$ increases, the contribution from the fast Dirac cone becomes dominant. The additional transitions involving the flat bands and the fast Dirac cone substantially reduce the region where undamped plasmons can exist, similarly to the conventional $\alpha-\mathcal{T}_3$. Consequently, stable plasmons are observed only for relatively small values of $\alpha$ or at very small wave vectors. These unusual electronic and collective properties make the Kek-$\alpha$ model a promising platform for future plasmonic and nanoscale electronic applications.
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All authors Jean Marseille, Teresa Lee, Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs, Danhong Huang
Materials Science
EBSD and Subtle Crystallographic Differences - A Study of Resolving Interlayer Spacings in Nb-Ni and Nb-Co mu-phases
Lukas Berners, Nisa Ulumuddin, Annika Baum et al. (+9 more)
In ordered intermetallics, slight variations in
lattice site occupancy and specific interlayer spacings have been identified as the sources of significant changes in critical resolved shear stress and therefore how a given phase may affect
alloy properties. So far, atom positions and
lattice site occupancies have traditionally been characterised by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD), which are methods that offer either local detail or high statistical significance but not both. Electron backscatter diffraction (EBSD), by contrast, provides high spatial resolution across large sample areas and therefore, has the potential to enable the local investigation of interlayer spacing and site
lattice occupancy with improved statistical reliability. The objectives of the study are to
benchmark EBSDs capability for resolving these subtle features and to correlate them with compositional and mechanical properties. In this case study, we therefore show that EBSD can resolve key crystallographic features of mu-phase intermetallics, specifically interlayer spacings. We combine pattern matching with large-scale dynamical simulations of template libraries guided by XRD based information on
lattice parameters. For this, we generate structures that vary in the spacing between triple-layer and Kagome layer and in the site
lattice occupancy of the 3a site. This approach successfully predicts the change of interlayer spacing between Kagome and triple layers in Nb-Co and Nb-Ni mu-phases, in good agreement with XRD and HR-TEM.
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All authors Lukas Berners, Nisa Ulumuddin, Annika Baum, Silvia Richter, Khalil Rejiba, Joshua Spille, Siyuan Zhang, Christina Scheu, Joachim Mayer, Benjamin Berkels, T. Ben Britton, Sandra Korte-Kerzel
Superconductivity
Bulk Ising superconductivity in an intercalated TaSe2 bilayer structure
Yupeng Li, Zhaopeng Guo, Lihong Hu et al. (+17 more)
Ising
spin-orbit coupling in bulk systems has drawn considerable interest for its ability to conveniently construct
spin-orbit environments and enable exotic
quantum phenomena. In this work, we synthesize intercalated 2Hb-TaSe$_2$
bilayers with noncentrosymmetric structure and, through multifaceted analysis, present multiple lines of evidence for the emergence of bulk Ising superconductivity. Resistivity measurements reveal anisotropic superconducting behavior, with a remarkably large in-plane upper critical field $B_{c2}^{\|}$ that exceeds the Pauli limit $B_{p}$. Band structure calculations further show band splitting accompanied by out-of-plane
spin polarization. Collectively, these observations point to the presence of Ising superconductivity. Additional measurements of the thickness-dependent ratio $B_{c2}^{\|}$/$B_{p}$ and the superconducting diode effect not only further support the Ising superconducting nature of this material, but also reveal additional features of bulk Ising superconductivity evolving with thickness. Our findings provide valuable insights that may contribute to the search for bulk Ising
superconductors.
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All authors Yupeng Li, Zhaopeng Guo, Lihong Hu, Guoan Li, Siqi Wu, Xinyi Zheng, Xiao Deng, Zhiyuan Zhang, Anqi Wang, Xingchen Guo, Ziwei Dou, Peiling Li, Yuke Li, Fanming Qu, Guangtong Liu, Jin-Ke Bao, Guang-Han Cao, Li Lu, Jie Shen, Zhu-An Xu
Superconductivity
Anisotropic transport of Josephson vortices in atomic-layer superconductors on vicinal surfaces
Wenxuan Qian, Yash Chauhan, Ryohei Nemoto et al. (+3 more)
Atomic steps have strong influences on surface two-dimensional
superconductors. Josephson
vortices formed at the atomic steps under
magnetic fields may dominate transport phenomena at low temperatures, but its experimental verification is still lacking. Here, we report the
vortex transport properties of atomic-layer
superconductor Si(111)-$(\sqrt{7}\times\sqrt{3})$-In with vicinal surfaces, for which Josephson
vortices are directly observed by scanning tunneling microscopy. A sharp drop in resistance with decreasing temperature $T$, detected under out-of-plane
magnetic field $B$, reveals a distinctive anisotropy with respect to the atomic step direction. The anisotropy of sheet resistance, proportional to that of
vortex mobility, amounts to the order of $10^3$ at intermediate
magnetic fields. In the high-$T$ and low-$B$ region, Josephson
vortices exhibit thermally excited creep motions with anisotropic activation energy $U_\mathrm{act}$. A further increase in $B$ suppresses $U_\mathrm{act}$ toward zero anisotropically, resulting in one-dimensional pinning-free
vortex flow at $0.10 \lesssim B \lesssim 0.20$ T. At the lowest temperatures, the
vortex motion is governed by
quantum tunneling. A $B$-$T$ phase diagram constructed based on these measurements reveals multiple regions characterized by directionally dependent
vortex-transport mechanisms.
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All authors Wenxuan Qian, Yash Chauhan, Ryohei Nemoto, Keisuke Sagisaka, Shunsuke Yoshizawa, Takashi Uchihashi
Statistical Mechanics
Noise-enhanced temporal boundary states in non-Hermitian systems
Jielong Zhang, Bozheng Xue, Xianfeng Man et al. (+1 more)
Time-periodic modulation introduces a synthetic degree of freedom to manipulate topological phases. This synthetic dimension can trigger a phase transition that localizes a boundary state at the temporal interface. Noise is widely deemed a fundamental threat to topological protection, universally anticipated to weaken or even destroy topological states. Here, we introduce periodically repeated temporal noise and fully random temporal noise into a 2D periodically driven non-Hermitian system. Paradoxically, under ensemble averaging, such temporal noise drives an exponential enhancement of the response intensity at the temporal interface. An averaged superoperator analysis shows that the noiseless band structure is preserved under both types of noise. Yet the noise increases the growth rate of growing modes while suppressing the decay rate of decaying ones. Finally, we experimentally realize the noise-enhanced temporal boundary state in a robotic metamaterial network. This finding establishes temporal noise as a constructive ingredient, enabling the unambiguous emergence of topological states and conferring exceptional robustness upon topological devices.
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All authors Jielong Zhang, Bozheng Xue, Xianfeng Man, Baizhan Xia
Soft Condensed Matter
From oligomers to entangled polymers: How to train a transferable machine learning interatomic potential
Mirko Fischer and Andreas Heuer
Over the past decade, Machine Learning Interatomic Potentials (MLIPs) have emerged as a powerful technique for performing molecular dynamics (MD) simulations with nearly ab initio accuracy. Alongside the development of new descriptors and advanced machine learning architectures, sophisticated procedures for the generation of diverse and accurate reference
datasets have been established. To date, research has focused primarily on MLIPs for crystalline or amorphous inorganic and small molecular systems; however, large macromolecules such as
polymers remain underrepresented in the literature, despite beeing an important class of materials. In this work, we investigate several aspects of developing MLIPs for
polymers, utilizing polyethylene as a representative, yet simple model system. First, we compare various local atomic descriptors, identifying the Atomic Cluster Expansion (ACE) as the most effective for this application. Second, we implement and automatized active learning scheme to efficiently generate diverse training data and demonstrate that ACE potentials fitted on small oligomers are transferable to larger
polymers. Given that the accurate reproduction of the density depends critically on a correct description of intermolecular interactions, which are far more complex to learn than intramolecular interactions, we carefully evaluate the performance of the ACE potentials with respect to non-bonded interactions. By utilizing the computationally efficient OPLS-AA force field as a ground truth reference, we are able to perform a direct comparison of nanosecond-scale MD trajectories resulting from the ACE and reference potential. We find that the ACE potential accurately reproduces key thermodynamic, structural and dynamical properties.
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Statistical Mechanics · Cross-listed from physics.bio-ph
Funnel-like protein energy landscapes emerge from functional evolution under thermal fluctuations
Norifumi Maruyama and Macoto Kikuchi
Foldable
proteins exhibit funnel-like energy landscapes, but their
evolution under selection for function remains unclear. We study this in a
lattice protein model, defining fitness as the
equilibrium probability of a fixed active-site motif and using multicanonical sequence sampling. At intermediate temperature, rare high-fitness sequences show funnel-like energy and double-well free-energy landscapes. At very low temperature, abundant high-fitness sequences retain glass-like landscapes. Thus, thermal fluctuations turn a local functional requirement into a global structural constraint.
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Soft Condensed Matter · Cross-listed from physics.bio-ph
Water and the Many-Body Imagination
Albert Libchaber and Tsvi Tlusty
An electron crosses the cold
Fermi sea. The sea
recoils, screens, remembers. It returns the electron dressed: a quasiparticle with a mass, a lifetime, and a Green function. This was Nozières' lesson. We carry it to water. Electrons become dipoles; the
Fermi sea becomes a hydrogen-bonded polar
liquid. We ask the same question: can the collective modes of water live long enough and reach far enough for molecular machines to interact and synchronize?
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Mesoscale and Nanoscale Physics
Time-dependent Berry curvature and quantum metric of Floquet-Bloch states
S. Sajad Dabiri and Reza Asgari
The
quantum geometry of Bloch bands, characterized by the Berry
curvature and the
quantum metric, underpins a wide range of linear and nonlinear responses in static systems. Here, we extend this framework to periodically driven (Floquet) systems by introducing a time-dependent Berry
curvature and
quantum metric defined directly in the Floquet-Bloch basis. We derive optical sum rules that relate the
Fourier components of these
geometric quantities to the optical conductivity and demonstrate that, under ideal Floquet-band occupations, the first-order DC
Hall and longitudinal responses at harmonic frequencies vanish identically. We further introduce a mixed Berry
curvature involving time and momentum derivatives, which gives rise to a non-adiabatic quantized charge-pumping mechanism that occurs naturally during each driving period without requiring adiabatic
evolution. In addition, we identify the time-domain
quantum metric as a measure of the energy fluctuations of a Floquet band and interpret its mixed components as quantifying polarization-energy correlations. A comprehensive
symmetry analysis reveals how time-reversal, sublattice (
chiral), particle-hole, inversion, rotational, and reflection
symmetries constrain the time-dependent
quantum geometric tensor and its associated topological invariant. Numerical simulations of the Rudner-Lindner-Berg-Levin model and a fully symmetric Floquet model confirm the analytical predictions. These results establish the time-dependent
quantum geometric tensor as a unified framework for describing the
geometric, topological, and dynamical properties of periodically driven
quantum systems, with direct implications for optical spectroscopy,
quantum transport, and topological charge-pumping experiments.
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Strongly Correlated Electrons
Magnetic circular dichroism of THz modes and selection rules of Raman-active optical phonons in the polar altermagnet candidate \ce{Mn2Mo3O8}
F. Schilberth, K. Vasin, M. Knauft et al. (+14 more)
We investigated the
magnetic and vibrational excitations in the collinear altermagnet candidate \ce{Mn2Mo3O8} by temperature dependent Raman scattering and magneto-optical THz time-domain transmission spectroscopy. By comparison to ab initio calculations accurately capturing the eigenfrequencies of the vibrational eigenmodes, we identify all optical
phonons, including the lowest-lying Raman modes of $A_1$ and $E_2$ type, which had remained elusive in a previous Raman study. Moreover, we compare the selection rules for optically active
phonons in the paramagnetic and the magnetically ordered phases of \ce{Mn2Mo3O8} and analyze the Raman selection rules with respect to pseudo-angular momentum conservation. No evidence of the expected splitting of the degenerate paramagnetic $E_2$ optical
phonons into modes with circular polarization upon
magnetic ordering could be resolved, likely due to weak
spin-orbit coupling typical for Mn$^{2+}$. In contrast, we observe strong
magnetic circular dichroism at a broad THz excitation band, emerging in the magnetically ordered state. This band, potentially originating from two-
magnon excitations, is only electric-dipole active and features a field-dependent two-component fine structure. Its
magnetic circular dichroism vanishes above the
spin-flop transition at 4~T.
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All authors F. Schilberth, K. Vasin, M. Knauft, M. Kondákor, M. Vuckovic, N. Herrmann, K. Penc, M. Minola, B. Keimer, V.A. Martinez, K. Panda, A.A. Sirenko, L. Prodan, V. Tsurkan, A.A. Tsirlin, I. Kézsmárki, J. Deisenhofer
Strongly Correlated Electrons
Spin-orbit-entangled frustrated magnetism in fcc Ba$_2$(Yb,Nd)NbO$_6$ double perovskites
S. M. Hossain, Sk. Soyeb Ali, S. Mohanty et al. (+7 more)
The search for candidate Kitaev materials has largely focused on 4$d$ and 5$d$ transition-metal compounds with various
lattice geometries. In contrast, investigations of rare-earth 4$f$ systems have thus far been restricted mainly to honeycomb and triangular
lattices. In this work, we investigate the rare-earth-based double perovskites Ba$_2$YbNbO$_6$ and Ba$_2$NdNbO$_6$, which crystallize in a face-centered cubic structure. Magnetization and heat-capacity measurements establish isolated ${j_{\rm eff}} = 1/2$ Kramers doublet ground states arising from strong
spin-orbit coupling (SOC) and
crystal electric-field effects, which are further supported by density-functional theory calculations. Millikelvin-temperature thermodynamic measurements reveal long-range
magnetic order with moderate frustration in both compounds. The emergence of
magnetic order may be understood within an order-by-disorder scenario, as theoretically proposed for rare-earth fcc
lattices with finite Kitaev interactions. Our results thus identify Ba$_2$YbNbO$_6$ and Ba$_2$NdNbO$_6$ as promising rare-earth
spin-orbit-entangled magnets and motivate further experimental and theoretical investigations aimed at determining the complete exchange tensor to elucidate the microscopic origin of the underlying
magnetic interactions.
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All authors S. M. Hossain, Sk. Soyeb Ali, S. Mohanty, R. Kolay, M. P. Saravanan, A. K. Yogi, Y. Tokiwa, R. Nath, S. K. Panda, M. Majumder
Disordered Systems and Neural Networks
Predictive Formulas for Scattering Mean Free Path for General Disordered Dielectric Media Beyond the Long-Wavelength Regime
Jaeuk Kim and Salvatore Torquato
We derive predictive formulas for the scattering mean free path $\ell_s$ of statistically homogeneous two-phase dielectric media in dimensions $d=1,2,3$. Unlike Mie-based estimates limited to identical circular or spherical scatterers, the formulas apply to arbitrarily shaped and polydisperse particulate media as well as nonparticulate media, with microstructure entering through the spectral density. The formulas are based on the exact strong-contrast expansion for the effective dynamic dielectric constant. We apply them to five nonhyperuniform and hyperuniform models and validate selected cases using finite-difference time-domain simulations. For $k_1/s \lesssim 1$, where $k_1$ is the incident wavenumber and $s$ is the specific surface, the predictions agree well with simulations and are consistent with Mie theory where applicable, while improving accuracy for two-dimensional transverse-
magnetic polarization. Mie estimates become more accurate for $k_1/s \gtrsim 1$. For hyperuniform media with $\widetilde{\chi}_V(k)\sim k^\alpha$ at small $k$, the theory predicts $\ell_s\sim k_1^{-(d+1+\alpha)}$; stealthy hyperuniform media are transparent over a finite wavenumber interval. These results provide a microstructure-based route to predict and design wave transport in general disordered dielectric materials.
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Statistical Mechanics · Cross-listed from quant-ph
On Identification of Heat and Work in Quantum Many-Body Systems with Local Operations and Classical Communication
Hiroaki Matsueda
How we identify heat and work is a fundamental question in modern
quantum thermodynamics. Usually, heat and work are attributed to changes in the density
matrix and the
Hamiltonian, respectively, during time-
evolution processes in
quantum systems. Recently, it has been recognized that this identification is ambiguous. Furthermore,
quantum thermodynamics involving
quantum measurement is still under development. Motivated by these on-going works, we consider a
quantum many-body system from which we extract energy by local operations and classical communication (LOCC) according to the
quantum energy teleportation (QET) protocol. The central idea to define heat and work unambiguously is based on a sharp insight into the optimization condition of LOCC. When LOCC is optimized, the extractable energy by QET becomes a daemonic ergotropy; thus, it can be attributed as work. On the other hand, when LOCC is not optimized, we have not squeezed out all the energy with the
unitary operation. It means there is uncontrollable energy left in the system. The uncontrollable energy can be attributed as heat after careful treatment of many-body interactions. The heat term consists of nonlocal correlation due to communication between remote participants, and the correlation cannot be directly observed for the participant in the subsystem. Thus, this feature is consistent with the traditional perspective of heat as an uncontrollable energy. To deeply understand the nature of heat, we derive two types of generalized Clausius inequality in our effective
quantum thermodynamics, and discuss the direction of the inequality. To justify our perspective, we examine a one-dimensional Kitaev-like model and discuss the physical meaning of effective temperature in our thermodynamics.
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Statistical Mechanics · Cross-listed from q-fin.TR
Exactly solvable model for the diffusive price-dynamics paradox under long-range correlated market-order flow
Yuki Sato, Shunta Fujiwara and Kiyoshi Kanazawa
We develop an exactly solvable nonlinear time-series model by incorporating the square-root price-impact law into the Lillo–Mike–Farmer (LMF) model to resolve the diffusive price-dynamics paradox under predictable
market-order flow. In financial
market microstructure, it is well established that the price dynamics are approximately described by Brownian motion at long times. However, it is also well-known that
market-order flow is clearly predictable due to long-range correlations, as mathematically formulated by the LMF model. Since
market orders have a positive price impact in general, predictable
market-order flow seems to contradict Brownian price dynamics. In this work, we resolve this diffusive price-dynamics paradox by developing nonlinear time-series models that generalize the LMF model based on the square-root price-impact law. Our time-series models can be mathematically mapped onto the Lévy-walk framework—an exactly solvable class of non-Markovian
stochastic processes developed in statistical physics. We prove that the price dynamics are diffusive at long times under the square-root law even under predictable
market-order flow. Our work highlights the crucial practical importance of the square-root law in understanding the microstructural foundation of the Efficient
Market Hypothesis.
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