Materials Science
Substrate-dependent electrical transport in individual single-walled carbon nanotubes grown across SiO$_2$ and hexagonal boron nitride
Yuanjia Liu, Taiki Inoue and Yoshihiro Kobayashi
The electronic transport properties of carbon nanotubes (CNTs) are strongly affected by their surrounding environment, making the underlying substrate a critical factor for device performance. Here, we demonstrate enhanced carrier transport of individual single-walled CNTs on hexagonal boron nitride (hBN) by directly comparing CNT channels on SiO$_2$ and hBN within the same nanotube. This within-tube comparison removes tube-to-tube variability in chirality, diameter, and defect density, allowing the intrinsic substrate effect to be evaluated more reliably. The CNTs were synthesized using gas flow-directed growth, which yields long, well-aligned CNTs without transfer processes, allowing a single nanotube to extend across different substrate regions. Multichannel field-effect transistors fabricated along an individual CNT exhibit clear ambipolar characteristics. CNT channels on hBN consistently exhibit higher field-effect mobility than those on SiO$_2$. In contrast, temperature-dependent transport near the charge neutrality point exhibits thermally activated behavior with similar activation energies (15-20 meV) on both substrates, indicating that the intrinsic small bandgap of CNTs is largely unaffected by the substrate. These results provide direct evidence that hBN enhances low-field carrier transport in CNTs and establish a foundation for the fabrication of high-performance electronics based on hBN-supported CNTs.
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Mesoscale and Nanoscale Physics
Modification of Damon-Eshbach magnetostatic mode spectra in ferromagnet/paramagnet bilayer
M. A. Kuznetsov
Using the magnetostatic approximation, we calculate the spectra of bulk and surface
spin waves in an in-plane magnetized ferromagnet/paramagnet
bilayer. Due to the dipolar coupling between the layers, the paramagnet becomes polarized, which in turn modifies the spectrum of the Damon-Eshbach magnetostatic modes. We assume that the paramagnet is characterized by a
magnetic susceptibility, $\chi \propto 1/(T-T_C)$, which reaches large values when the system temperature $T$ is close to the Curie temperature $T_C$. We find the conditions under which surface
spin waves become unidirectional, i.e., capable of carrying energy in only one direction, and determine the magnitude of their frequency nonreciprocity. We demonstrate the possibility of switching the unidirectional wave regime on and off by varying the external
magnetic field or temperature, making the ferromagnet/paramagnet system an attractive platform for tunable magnonic logic devices.
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Materials Science
First-principles calculations of spin-split bands in chiral hybrid organic-inorganic perovskites ($R$/$S$-PEA)PbI$_3$ and ($R$/$S$-NEA)PbI$_3$
Tetsuya Furukawa, Kazushi Nakano, Youta Suzuki et al. (+3 more)
Chiral hybrid organic-inorganic perovskites provide a promising platform for investigating the physics of chirality-driven
spin-split bands because they combine robust molecular chirality with strong
spin-orbit coupling from heavy inorganic ions. First-principles calculations including
spin-orbit coupling are performed for the one-dimensional
chiral perovskites ($R$/$S$-PEA)PbI$_3$ and ($R$/$S$-NEA)PbI$_3$ to compare their
spin-split band structures and to identify the factors controlling their differences. In ($R$/$S$-PEA)PbI$_3$, the lowest conduction bands predominantly consist of Pb orbitals, whereas in ($R$/$S$-NEA)PbI$_3$, they are formed by hybridization between Pb orbitals and the lowest unoccupied molecular orbital of NEA. Both compounds exhibit pronounced
spin splitting near the valence-band maximum and conduction-band minimum. The effective
spin splitting of the edges of the valence bands is stronger in ($R$/$S$-NEA)PbI$_3$, despite similar linear-in-$k$ splitting coefficients near the relevant high-
symmetry points. This enhancement originates from larger gaps induced by
spin-orbit coupling at high-
symmetry points and band (anti)crossings in the multiband structure. For a given molecular handedness, the PEA- and NEA-based compounds exhibit opposite
spin textures, consistent with the opposite
chiral distortions of the [PbI$_6$]$^{4-}$ octahedra and with the previously observed opposite signs of circular dichroism. Group-theoretical analysis for the nonsymmorphic space group $P2_12_12_1$ further accounts for band sticking,
symmetry-enforced degeneracies, and the disappearance of
spin polarization at specific Brillouin-zone-boundary points. These results provide a solid foundation for future studies of chirality-dependent electromagnetic responses, including circular dichroism, in
chiral hybrid organic-inorganic perovskites.
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All authors Tetsuya Furukawa, Kazushi Nakano, Youta Suzuki, Takumi Kaneko, Ayumi Ishii, Tetsuaki Itou
Materials Science · Cross-listed from cs.AI
Graph-Native Reinforcement Learning Enables Traceable Scientific Hypothesis Generation through Conceptual Recombination
Subhadeep Pal, Shashwat Sourav, Tirthankar Ghosal et al. (+1 more)
Accelerating materials discovery requires AI systems that can generate scientifically valid hypotheses through multi-step, domain-grounded
reasoning. Standard large
language models often produce fluent but weakly traceable responses to open-ended materials design problems, making it difficult to determine whether final answers are supported by coherent intermediate
reasoning. We develop Graph-PRefLexOR, a family of graph-native
reasoning models fine-tuned with Group Relative Policy Optimization (GRPO) to organize
reasoning into explicit phases for mechanism exploration, graph construction, pattern extraction, and hypothesis synthesis. This design links neural
language generation with symbolic relational structure, enabling causal connections to be constructed, inspected, and reused. On 100 open-ended questions from materials science and mechanics literature, Graph-PRefLexOR achieves 40-65% improvements over corresponding base models, with the largest gains in
reasoning traceability.
Embedding analyses show broader semantic exploration and approximately 2-3 times greater semantic diversity than baselines. Semantic backtracking and layer-wise hidden-state analyses further show stronger
alignment between structured
reasoning and final answers. Finally, test-time graph expansion reveals that additional compute primarily increases long-range conceptual recombination within a bounded semantic space, rather than simply expanding semantic coverage. These results establish graph-native reinforcement learning as a pathway toward interpretable AI systems for scientific hypothesis generation in materials design and other scientific applications.
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All authors Subhadeep Pal, Shashwat Sourav, Tirthankar Ghosal, Markus J. Buehler
Mesoscale and Nanoscale Physics
Symmetry Classification of Non-Reciprocal Responses in Multiterminal Ring Devices
Chen-How Huang and Tero T. Heikkilä
We present a
symmetry-based framework to classify the non-reciprocal responses of multiterminal ring
quantum devices. The device is modeled as a ring of $n$ vertices, where a binary variable $e_k\in\{+1,-1\}$ on each bond encodes the preferred direction of signal flow between terminals. Non-reciprocity corresponds to a preferred current configuration on the ring, and the
symmetry group of the device partitions all $2^n$ configurations into equivalence classes(orbits) characterized by a topological winding number $W$. Using the minimal non-trivial case $n=3$, we establish two results independent of microscopic details. First, lifting the degeneracy within an orbit generates non-reciprocal responses. For $n=3$ this requires simultaneous breaking of both time-reversal $T$ and spatial inversion $I$. Breaking either alone is insufficient. Second, the residual geometry
symmetry after $T$ and $I$ are broken determines which responses are observable. For an isosceles triangular geometry, only two types of response are allowed: uniform circulation (all bonds carrying current in the same direction) and semi-circulation with the reversed bond on the geometrically distinct base. Semi-circulation with the reversed bond on either equal leg is
symmetry-forbidden. Both predictions are validated using a minimal toy model of three
quantum dots coupled to superconducting baths, which demonstrates a reactive
quantum circulator response.
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Superconductivity
Imaging superconducting weak spots through vortex-assisted THz near-field photovoltage
Sergio J. Salvía-Fernández, Ekaterina Khestanova, Zoe Velluire-Pellat et al. (+9 more)
Nanoscale inhomogeneities are a defining feature of many superconducting materials, yet their local electromagnetic response has remained difficult to access experimentally. This is because their relevant energy scale lies in the terahertz range, where wavelengths – on the order of hundreds of microns – are too large to spatially resolve nanoscopic variations. Here, we demonstrate the first application of THz near-field photovoltage nanoscopy in a
superconductor, achieving 300 nm spatial resolution at 2.52 THz. Scanning a current-biased NbN strip, we reveal photovoltage peaks within the bulk associated with nanoscopic defects of reduced superfluid density. The observed photovoltage follows the
evolution of the
vortex-dissipative state and is attributed to enhanced
vortex-antivortex pair nucleation at defect sites. Together, these results open a direct route to probing how material inhomogeneities influence light-matter interactions in
superconductors, with implications for superconducting devices and strongly inhomogeneous systems such as high-Tc and moiré materials.
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All authors Sergio J. Salvía-Fernández, Ekaterina Khestanova, Zoe Velluire-Pellat, Leonardo R. Cadorim, Sergi Batlle-Porro, David A. Czaplewski, Johann Osmond, Sebastian Castilla, Adrian Bachtold, Milorad V. Milošević, Aharon Kapitulnik, Frank H.L. Koppens
Materials Science
Strengthening and interface-mediated plastic co-deformation in an ultrafine Cr-Ni eutectic: A nanomechanical investigation
Arkajit Ghosh, Mustafa Tobah, Jianing Zhou et al. (+2 more)
Ultrafine eutectic
heterostructures provide a stringent test of plasticity in high-strength materials, where deformation must be accommodated through interfaces and strain gradients. Room temperature ductility is typically limited by premature fracture of the hard phase, leaving open the fundamental questions regarding the interface spacing, atomic structure and local chemistry that enable plastic co-deformation. Here we address this question using a model system of Cr-Ni binary
alloy, processed via electron-beam powder bed fusion that produces a lamellar eutectic microstructure of Cr-rich BCC and Ni-rich FCC phases, with an average interlamellar spacing of ~450 nm. Atomic-resolution STEM revealed a stepped semi-coherent FCC/BCC interface with the Kurdjumov-Sachs orientation relationship and Ni-enrichment confined to a few atomic planes on the BCC side. In situ micro-scale compression and tension tests in SEM demonstrate high flow stresses coupled with large plastic strains without cracking, indicating stable accommodation of plastic incompatibility. Correlative TEM/HR-STEM establishes a deformation sequence: initial plasticity is dominated by strain-gradient driven dislocation accumulation in the FCC lamellae adjacent to interfaces, followed by deformation twinning in FCC and local interfacial shear and reorientation. The BCC phase subsequently develops a high density of mobile dislocations. Atomistic modeling has been employed to understand the influence of the FCC/BCC interface atomic structure and chemistry on the slip activation in the hard phase. These findings show that nanoscale confinement, stepped K-S interfacial structure, and interfacial chemistry collectively promote dislocation glide in a hard phase below its monolithic brittle to ductile transition temperature, and plastic codeformation at high flow strengths.
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All authors Arkajit Ghosh, Mustafa Tobah, Jianing Zhou, Jian Wang, Amit Misra
Superconductivity
Characterization of Hydroxyls in Surface Oxide of Superconducting Tantalum and Their Mitigation in Quantum Circuits
Ekta Bhatia, Nicholas Pieniazek, Aleksandra Biedron et al. (+7 more)
Recently, tantalum (Ta) has gained
attention in superconducting
quantum circuits due to the longer coherence times achieved when replacing niobium (Nb) in capacitor pads. Previous literature shows that surface
oxides that form upon ambient exposure on superconducting metals such as Ta, Al, and Nb host two-level system (TLS) defects, which are a leading source of microwave loss and decoherence. While the surface
oxides of Nb and Al have been extensively studied, Ta
oxides remain less well understood. Using secondary ion mass spectrometry of alpha-Ta films deposited at 300 mm wafer scale, we show for the first time that hydroxyls accumulate in the Ta suboxide region above the underlying Ta. Angle-resolved X-ray photoelectron spectroscopy shows that the surface region is dominated by Ta2O5, with sub-stoichiometric TaOx present in between the Ta2O5 and underlying Ta. The thickness of the tantalum
oxide is confirmed by transmission electron microscopy. We demonstrate that [OH] incorporation can be suppressed by replacing the native
oxide with an
oxide formed during chemical mechanical planarization of alpha-Ta films. Our findings support the hypothesis that TLS defects are non-uniform within the
oxide thickness and suggest hydroxyls as a probable molecular origin of these loss channels. Furthermore, we show the feasibility of
plasma nitridization as a method to decrease hydroxyl loading on alpha-Ta surfaces. The modulation of hydroxyl content through surface engineering of alpha-Ta can enable the fabrication of more robust, high-coherence superconducting
quantum circuits by addressing a potential TLS source.
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All authors Ekta Bhatia, Nicholas Pieniazek, Aleksandra Biedron, Sandra Schujman, Hunter Frost, Zhihao Xiao, Jakub Nalaskowski, Kevin Musick, Thomas Murray, Satyavolu Papa Rao
Materials Science
Two-dimensional vertically polarized Hg3AsSe4I monolayer for efficient photocatalytic water-splitting: promoting carrier separation by intrinsic electric field and Rashba effect
Xinfeng Chen, Wenchao Shan, Fengfeng Ye et al. (+1 more)
Efficient separation of photo-excited electron-hole pairs is essential for developing the high performance photocatalysts towards light-driven water-splitting applications. To this end, pho tocatalytic performances of two-dimensional (2D) semiconducting ferroelectric (FE) materials with out-of-plane polarizations have been extensively explored. However, out-of-plane polarizations in 2D FE materials are susceptible to the critical thickness limitation and can be easily compensated by surface adsorbates. On the other hand, 2D vertically polarized materials with stable and ir reversible out-of-plane polarizations may overcome the critical thickness limitation, enabling the practical advantage for spatial separation of photo-excited electron-hole pairs during the photo catalytic reactions. In the current work, 2D vertically polarized Hg3AsSe4I, an experimentally synthesized van der Waals (vdW) layered material, has been systematically investigated as a high performance 2D photocatalyst. Owing to its semiconducting band gap suitable for visible-light absorption, high carrier mobility, and desirable band edge
alignment ideally matching water reduc tion and oxidation potentials, Hg3AsSe4I monolayer fulfills both optical and electronic prerequisites for photocatalytic water-splitting reactions. Besides the stable vertical polarization able to persist in Hg3AsSe4I monolayer, the dual mechanism for efficient separation of photo-excited carriers has also been demonstrated. Rashba
spin-orbit coupling (SOC) of large strength emerges within 2D Hg3AsSe4I, splitting the band edges into
spin-resolved band branches with unique
spin-momentum locking characters.........
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All authors Xinfeng Chen, Wenchao Shan, Fengfeng Ye, Gaoyang Gou
Disordered Systems and Neural Networks
Non-self-averaging topological Anderson insulator
Zheng-Wei Zuo and Jun-Chong Liu
Current research on the disordered topological
quantum phases primarily focuses on the uncorrelated and short-range correlated disorder regime. These topological Anderson
insulators are typically self-averaging. However, topological
quantum systems with long-range correlated disorder have received limited
attention due to the absence of tractable analytical methods. In fact, the long-range correlated disorder introduces more complex effects on topological
quantum states. Here, we demonstrate that the long-range correlated disorder could induce anomalously statistical feature where the topological Anderson states become non-self-averaging, and the phase diagram is strongly dependent on individual disorder configurations. We term this statistical phase the non-self-averaging topological Anderson
insulator. The non-self-averaging property is identified by the non-vanishing finite values of the relative variance of the Lyapunov exponent in the thermodynamic limit, alongside the non-Gaussian distributions of the Lyapunov exponent. Consequently, the topological properties of a single disordered sample deviate from the ensemble average, causing a breakdown of the central limit
theorem. The non-self-averaging topological Anderson
insulator provides insights into the interplay between correlated disorder and
topology.
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Soft Condensed Matter
The Role of Compressibility in Modified Quasi-Linear Viscoelasticity: A Comparison of Simple Shear and Torsion
Valentina Balbi and Griffen Small
We investigate the role of compressibility in the modified quasi-linear viscoelastic (MQLV) constitutive framework for soft solids at finite strain, where shear and bulk responses are governed by distinct relaxation functions. Analytical and semi-analytical results are derived for simple shear and torsion, under incompressible and slightly compressible assumptions. We show that compressibility affects the response only when volume changes occur: under isochoric deformations, the bulk contribution vanishes, while even small deviations from isochoricity significantly alter the normal response. Shear stress and torque are largely insensitive to compressibility, whereas normal stress and axial force exhibit pronounced sensitivity due to the coupling between shear and bulk relaxation. We further demonstrate that volumetric effects interact with the Poynting effect: in simple shear they oppose each other, reducing relaxation, while in torsion they reinforce each other, enhancing it. These trends agree with
brain tissue experiments but reveal limitations of the slightly compressible model for highly compressible materials, such as agarose gels. Overall, the results emphasise the importance of accounting for compressibility in modelling normal stress responses and motivate the development of fully compressible formulations and numerical implementations.
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Materials Science
Vanadium superconducting microwave resonators on silicon wafers
Y. Fujita, Y. Urade, Y. Hibino et al. (+4 more)
Understanding the correlation between material properties and microwave losses in superconducting films is a crucial subject for developing low-loss materials for
quantum circuits. We focus on vanadium (V) as a novel material for superconducting
quantum devices and discuss loss in V films in relation to their structural properties. Using a sputtering method, we grow four V-film structures on (001)-oriented Si wafers, employing Nb and Ta as the buffer and capping layer materials, respectively: Nb/V/Ta, Nb/V, V/Ta, and V. X-ray diffraction and atomic force microscopy reveal that the V films grown on the Nb buffer layers have higher uniformity of
lattice orientation and smaller grain size than that directly grown on the Si wafer. Coplanar waveguide resonators are fabricated from the four V-film structures, and averaged
photon number ($\langle n_{\rm ph} \rangle$) dependences of internal quality factor ($Q_{\rm int}$) are obtained by performing microwave measurements. By analyzing the obtained $Q_{\rm int}$ vs $\langle n_{\rm ph} \rangle$, it is found that loss at the V surface is dominated by $\langle n_{\rm ph} \rangle$-independent non-two-level-system (non-TLS) losses, which can be mitigated by introducing the Ta capping layer. Furthermore, the V films on the Nb buffer layers exhibit lower $Q_{\rm int}$ in the $\langle n_{\rm ph} \rangle$ range from 10$^{0}$ to 10$^{6}$ and higher non-TLS loss than that directly grown on Si wafers, even though the former has higher
lattice-orientation uniformity than the latter. Origins of these trends might be relevant to V
oxides, of which presence at surfaces and grain boundaries in bulk regions in the V resonators is suggested by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, and/or V hydrides.
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All authors Y. Fujita, Y. Urade, Y. Hibino, M. Tsujimoto, K. Inomata, G. Fujii, W. Mizubayashi
Mesoscale and Nanoscale Physics
Electrical control of spin photocurrent in a magnetoelectric oxide Cr$_2$O$_3$
Zhuo-Cheng Gu and Hiroaki Ishizuka
Controlling magnetism by electric field or current is a central topic in spintronics. In this work, we argue that the
magnon spin photocurrent can also be controlled by the electric field in magnetoelectrics. Taking Cr$_2$O$_3$ as an example, we demonstrate how the
spin current is modified by the electric field, using nonlinear response theory. We find that the Dzyaloshinsky–Moriya interaction induced by the applied field plays a key role in modifying
spin-current conductivity, which exhibits pronounced anisotropy with respect to the light polarization. In particular, both the resonance frequency and the peak intensity show distinct dependences on the external electric field $E$, demonstrating electrical control of the
spin photocurrent. In addition, we show that the two-
magnon processes give rise to a continuum spectrum, a consequence of the field-induced
spin canting. These results show that Cr$_2$O$_3$ is a promising platform for realizing electrically tunable
spin photovoltaic effect.
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Materials Science
Prediction of coherent interfaces between diamond and clathrate structures
Eva Pospíšilová and Marek Mihalkovič
Diamond (or its binary zincblende variant)-type structure can form coherent interface with clathrate type II via the common transitional layer known previously as a $(3\times 3)$-dimer-stacking fault (DS) reconstruction of the (111)-diamond surface. The generic $\sim 11\%$
lattice misfit can be eliminated in multicomponent
heterostructures such as Ge(diamond)/CsSn(clathrate) or InN(zincblende)/Ge(clathrate). Interface models subjected to ab-initio molecular dynamics annealing are stable up to the temperatures approaching melting point of the constituent systems, and in some studied cases the diamond/clathrate bonding is stronger than the intra-clathrate bonding, as evidenced by simulated crack experiments. Composition-calibrated
lattice-matching can stabilize even metastable clathrates as epitaxially grown films on the diamond/zincblende substrate.
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Mesoscale and Nanoscale Physics
Universal logic circuit for gate-controlled superconductor-based switches operating at liquid-helium temperatures
Martin Berke, Lőrinc Kupás, Tosson Elalaily et al. (+3 more)
The observation of the gate-controlled supercurrent (GCS) effect in superconducting nanostructures initiated major research efforts toward the realisation of superconducting-based computing architectures. Here we introduce a universal logic
circuit that can be a promising superconducting building block of classical hybrid supercomputers. We demonstrate a functionally complete set of logic gates by realising the AND, OR, NOT and COPY gates. The general layout and scalability of our device, combined with recent experiments demonstrating fast switching and small voltage signals, make it a functional candidate in superconducting electronics. Our device enables the realization of all classical logic gates and the half-adder combinational logic
circuit using at most three nanowires, each uniquely configured with two side-gate electrodes.
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All authors Martin Berke, Lőrinc Kupás, Tosson Elalaily, Máté Sütő, Szabolcs Csonka, Péter Makk
Statistical Mechanics
Power-Law Relaxation of Non-Gaussian Parameter and Self-Dynamic Structure Factor in Multidimensional Rugged Energy Landscapes
Bimman Bagchi
Ruggedness of the underlying energy landscape gives rise to heterogeneous mobility and non-Gaussian
diffusion. We develop a theoretical framework for tagged-particle
diffusion in multidimensional rugged energy landscapes modeled as correlated quenched Gaussian random fields. Using the self-propagator and self-dynamic structure factor, we characterize finite-time
diffusion beyond the effective
diffusion coefficient. We determine the effects of dimensionality, spatial correlations, and initial preparation. By introducing a coarse-grained mobility field and a mobility-
memory approximation, we relate the non-Gaussian parameter to the time correlation of the mobility sampled by the particle. In the homogenized diffusive regime, the mobility correlation decays algebraically, leading to long-time relaxation of the non-Gaussian parameter as $t^{-1/2}$ in one dimension, $(\ln t)/t$ in two dimensions, and $t^{-1}$ for $d>2$, with amplitudes that depend on dimensionality and the initial ensemble. Our results show that rugged energy landscapes leave distinct signatures in the effective
diffusion coefficient, self-dynamic structure factor, and relaxation of non-Gaussian fluctuations.
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Superconductivity
Resilient $j$=3/2 superconductivity in topological semimetal YPtBi
Prathum Saraf, Nicholas A. Crombie, Rahul Sharma et al. (+11 more)
Cooper pairing in most of the known fermionic superfluids occurs via
spin-1/2 quasiparticle interactions that lead to
spin-singlet or
spin-triplet pairing. In the topological semimetal YPtBi, strong
spin-orbit coupling results in a band inversion between highly symmetric $s$- and $p$-like electronic bands and a degeneracy at the $\Gamma$ point that ensures the
manifold of $j$=3/2 quasiparticle states thrive near the
Fermi level, where superconducting pairing occurs. Here we study the effects of
magnetic and nonmagnetic disorder and carrier density on this exotic superconducting pairing state. By varying levels of disorder and carrier densities by nearly two and three orders of magnitude, respectively, we show that the superconducting critical temperature of YPtBi has a remarkable robustness, with little variation across this span. Our results suggest that superconductivity in YPtBi may reside in a regime where phase stiffness, rather than pair formation, governs the transition temperature. The insensitivity of Cooper pairing to dramatic changes in quasiparticle environment in a $j$=3/2
superconductor highlights a new form of protection realized in topological high-
spin superconductors.
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All authors Prathum Saraf, Nicholas A. Crombie, Rahul Sharma, Jared Z. Dans, Danila Sokratov, Carsyn L. Mueller, Ram Kumar, Hyunsoo Kim, Connor Roncaioli, Winslow Weiss, David Graf, Chandra Shekhar, Claudia Felser, Johnpierre Paglione
Strongly Correlated Electrons
Chuang Chen, Subir Sachdev and Zi Yang Meng
We present a
quantum Monte Carlo study of the transition between the insulating Néel state and the nodal $d$-wave
superconductor on the square
lattice at half-filling. We access a regime of frustrated
magnetic order without a sign problem using a parton representation of the electron in terms of fermionic spinons and bosonic chargons. Both partons move in a background $\pi$-flux (so the electron experiences no net flux) and are coupled to a
quantum fluctuating SU(2)
lattice gauge field. In contrast to earlier studies directly on the electronic degrees of freedom, we find evidence for a second-order deconfined
quantum phase transition at which both the Néel and $d$-wave superconductivity orders vanish continuously. We compute correlators of the spinon-chargon composite with the same
quantum numbers as the electron: we find a gapless Dirac dispersion inside the $d$-wave
superconductor, turning into a gapped dispersion in the antiferromagnet.
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Materials Science
The BiP-PRISM algorithm for fast and scalable core-loss STEM-EELS simulations
Philipp Pelz
Quantitative interpretation of atomic-resolution STEM-EELS requires dynamical simulation of the electron probe before and after core-loss transitions, which is computationally expensive. While the PRISM
algorithm accelerates this by reusing scattering
matrices, we introduce beam partitioning for both the probe-forming ($\mathcal{S}_1$) and detector-propagating ($\mathcal{S}_2$) PRISM
matrices to further reduce computational and
memory costs. Each
matrix is calculated on a sparse set of parent beams and reconstructed via natural-neighbor interpolation locally at the ionized atom. A locality result demonstrates that the total error is governed entirely by this on-atom reconstruction error. The resulting BiP-PRISM
algorithm removes per-scan exit wave propagation and significantly reduces
memory requirements, enabling full-resolution elemental mapping, 4D cubes, and momentum-resolved qEELS on consumer-grade GPUs. We characterize the approximation's validity regime and demonstrate the simulation of a
multimodal five-edge
oxide-interface map and an FePt nanoparticle Fe-L map at 5x
memory reduction, showing that the
algorithm achieves high accuracy with significantly lower computational demands.
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Soft Condensed Matter
Pattern formation in nonlinear dynamics of nematic liquid crystals above the flexoelectric instability threshold
E.S. Pikina, E.I. Kats, A.R. Muratov et al. (+1 more)
For many decades, researchers have been studying various types of electro-hydrodynamic instabilities in
liquid crystals. A significant amount of experimental data has been collected, however, the theoretical interpretations of the results typically rely on linear analysis. In response to this limitation, we investigate the nonlinear stage of the flexoelectric instability in nematics, focusing on
liquid crystals with a negative anisotropy in their dielectric permittivity and electrical conductivity. We base our analysis on a comprehensive set of nonlinear electro-hydrodynamic equations for these nematics influenced by an external alternating electric field. The equations predict an instability that is driven by the flexoelectric effect. In order to examine the peculiarities of this phenomenon, we use a model that was proposed in our previous publications, Refs. [1,2], which allows us to perform numerical simulation of nonlinear dynamics. We examine patterns that are formed above the instability threshold. Through numerical simulations, we have identified static and dynamic patterns that occur over a timescale that is much longer than the period of the external electric field. The static patterns are one-dimensional structures and dynamic patterns are standing or traveling one-dimensional waves. The type of the realized pattern depends on the material and experimentally controlled parameters. We found that the standing waves are stable with respect to small transverse perturbations, whereas the propagating waves are unstable. We present a Ginzburg-Landau-like phenomenology that applies near the instability threshold. This approach allows us to rationalize our numerical findings with a few parameters.
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All authors E.S. Pikina, E.I. Kats, A.R. Muratov, V.V. Lebedev
Materials Science
Atomic Cluster Expansion Potentials for Screw Dislocations in BCC Refractory Metals
Lei Zhang and Francesco Maresca
Accurate atomistic modeling of screw dislocations in body-centered cubic (bcc) metals remains challenging because their plasticity is governed by a complex dislocation glide behavior due to their compact three-fold symmetric core structure and a strongly temperature-dependent flow stress induced by the large Peierls barrier. In the context of group 6 (V, Nb, Ta) and group 5 (Mo, W) refractory metals (RMs), both classical interatomic potentials and some machine learning potentials consistently fail to reproduce density functional theory (DFT) Peierls barriers and the glide plane. Here, we developed an array of atomic cluster expansion (ACE) potentials for these RMs by extending an existing DFT database. The developed ACE potentials significantly improve the description of screw dislocation properties, achieving near-DFT accuracy for Mo and W and substantial improvement for V, Nb, and Ta. The results show that transferability to screw dislocation behavior depends sensitively on both database composition and element-specific energetics, and that achieving a single-humped Peierls barrier alone is not a sufficient validation metric for accurate prediction of dislocation glide. For Nb, Mo, and W, the developed ACE models also enable reliable calculation of kink-pair activation enthalpies, which are well described by both Kocks' law and a line-tension model.
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Strongly Correlated Electrons
Weak-coupling tensor cross interpolation impurity solver for nonequilibrium dynamical mean-field theory
Shuta Matsuura, Hiroshi Shinaoka, Philipp Werner et al. (+1 more)
Simulating nonequilibrium
quantum many-body systems remains a major challenge due to the exponential growth of the computational complexity with real time. Here we implement a nonequilibrium
impurity solver based on the weak-coupling expansion and the tensor cross interpolation (TCI), and apply it to nonequilibrium dynamical mean-field theory (DMFT). The method approximates the integrands of the high-dimensional integrals arising in the weak-coupling expansion in a tensor-train form, enabling efficient evaluations without
stochastic sampling and thereby mitigating the sign problem affecting continuous-time
quantum Monte Carlo (CT-QMC) methods.
Benchmark calculations for an exactly solvable nonequilibrium
impurity model agree well with the exact results and reveal a low-rank structure of the integrands. When applied to interaction-quench problems in the half-filled Hubbard model, the method reproduces fast thermalization at a critical interaction strength with accuracy comparable to CT-QMC. Away from half filling, where the sign problem becomes even more severe, the present approach remains well controlled, revealing a crossover instead of a sharply defined fast thermalization point in the 3/4-filled case. The solver can also be applied to steady-state DMFT problems, yielding accurate spectral functions in the metallic regime without analytic continuation.
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All authors Shuta Matsuura, Hiroshi Shinaoka, Philipp Werner, Naoto Tsuji
Disordered Systems and Neural Networks
Dependence of charge separation efficiency on the exciton-charge transfer offset and Gaussian disorder in organic solar cells
Maik Schwuchow, Carsten Deibel and Angela Thränhardt
State-of-the-art organic
solar cells increasingly rely on low-offset
semiconductor blends, challenging the traditional requirement of a large energetic driving force for efficient charge separation. In these systems, the energetic offset $\Delta E_{\mathrm{LE-CT}}$ between local
exciton (LE) and charge-transfer (CT) states approaches the thermal energy, making
exciton-CT hybridization and thermal repopulation of the
exciton level critical to device performance. In this work, we directly compare a macroscopic two-state rate model with three-dimensional kinetic Monte-Carlo (kMC) simulations to investigate microscopic charge separation dynamics and the role of Gaussian energetic disorder. We demonstrate that in the absence of disorder, the analytical rate model accurately reproduces kMC predictions for the whole range of $\Delta E_{\mathrm{LE-CT}}$. Specifically, the macroscopic model successfully explains horizontal shifts in the internal
quantum efficiency curves that arise depending on how the energetic offset is physically realized in the constituent molecules. We show that these variations can be captured entirely through the ratio of degeneracies of the LE and CT states, respectively. Introducing Gaussian energetic disorder into the kMC simulation reveals a distinct crossover behavior depending on $\Delta E_{\mathrm{LE-CT}}$. While disorder is mostly detrimental at large offsets, it can significantly boost efficiency at intermediate and low offsets. Thermalization of charge carriers within the disorder-broadened density of states creates an effective driving force allowing charge separation even at zero or negative energetic offsets.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Near-Field Characterisation of Guided Modes in WS2 Nanobeams and Quasi-Bulk Crystals
Zara S. Taylor, Luke M. Hallacy, Xuerong Hu et al. (+7 more)
The exceptionally high in-plane refractive index, low sub-bandgap absorption, and strong optical anisotropy of WS2 make it a promising material platform for next-generation integrated
circuits for nanophotonics. Its layered van der Waals structure further enables heterogeneous integration with silicon photonics and emerging two-dimensional optoelectronic materials. However, despite increasing interest in the waveguiding properties of WS2, experimental studies of wavelength-dependent modal confinement and attenuation remain limited. Additionally, though the extinction coefficient of WS2 is expected to be near-negligible beneath the bandgap, reported values span orders of magnitude, leading to large uncertainty in predicted modal decay lengths and wafer-scale integration feasibility. To resolve these ambiguities we perform hyperspectral cavity-enhanced imaging, determining high-resolution upper and lower bounds on the extinction coefficient of WS2 within the visible-NIR edge. We further employ scattering-type scanning near-field optical microscopy (s-SNOM) to probe TE0, TM0, and higher-order modes in both quasi-bulk and nanobeam WS2 waveguides across the 800-1400 nm spectral range, enabling identification of mode-specific trends in wavevector dispersion and loss. This work simultaneously assesses s-SNOM as a probe of waveguide performance, and we find that while absolute loss values depend on measurement geometry, s-SNOM reliably captures relative modal trends and provides upper bounds on propagation loss, supporting its use as a diagnostic tool for anisotropic waveguides. We further identify significant artefacts in nanobeam measurements arising from transverse interference and spatial sampling effects when the structure size approaches the excitation wavelength, which can shift extracted effective indices by up to 0.25.
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All authors Zara S. Taylor, Luke M. Hallacy, Xuerong Hu, Oliver T. Williams, Simone Strohmair, Fabian Felixberger, Alexander J. Knight, Timothy Chester-Parsons, Luke R. Wilson, Alexander I. Tartakovskii
Materials Science · Cross-listed from physics.ins-det
In-Situ Polarimetry in Collimated Magneto-Infrared Spectroscopy System
Zeping Shi, Wenbin Wu, Zhiwei Zhang et al. (+14 more)
Magneto-infrared spectroscopy under strong
magnetic fields provides a powerful probe of Landau quantization and field-induced collective excitations, yet its full potential has long been constrained by the lack of in-situ polarization control, because the highly divergent infrared beam propagating through narrow light tubes undergoes multiple wall reflections, leading to severe polarization degradation. Here we report a collimated magneto-infrared spectroscopy system that integrates continuous in-situ polarimetry. The system employs incident and exit collimation chambers forming a Kepler type optical architecture, which converts the large-aperture FTIR output into a low-divergence beam and strongly suppresses multi-reflection trajectories inside long gold-plated light tubes, thereby enhancing both optical throughput and polarization fidelity. A remotely controlled polarization module, consisting of an automated linear polarizer and a switchable Fresnel rhomb positioned entirely outside the high-field region, enables continuous in-situ tuning between linear, circular, and arbitrary elliptical polarization states without thermal cycling, manual realignment, or breaking
vacuum. Interchangeable compact focusing modules further support Faraday and Voigt geometries in both transmission and reflection experiments within a 50 mm magnet bore, providing efficient beam focusing and signal collection while maintaining polarization fidelity. The setup achieves a minimum root-mean-square noise of 0.0033%, an average noise of 0.0082%, and a linear polarization extinction ratio up to 40:1. We demonstrate the capability through continuous in-situ linear polarimetry and broadband circular polarimetry in the magneto-infrared spectroscopy of various single
crystals. This platform establishes a robust experimental framework for in-situ polarization-resolved magneto-infrared spectroscopy.
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All authors Zeping Shi, Wenbin Wu, Zhiwei Zhang, Yuhan Du, Chenyao Xu, Congming Hao, Xiangyu Jiang, Xin Chen, Guangyi Wang, Mingsen Zhou, Chunhui Pan, Wei Lu, Hao Shen, Haifeng Pan, Zhenrong Sun, Junhao Chu, Xiang Yuan
Mesoscale and Nanoscale Physics
Facet-selective ballistic supercurrent in a weak topological insulator
Prasanna Rout, Ankit Khola, Lalit Pandey et al. (+9 more)
Topological superconductivity is widely pursued by inducing superconducting correlations in topologically protected boundary states. In two dimensions, this strategy has been realized using one-dimensional topological edge modes, but in three-dimensional
crystals, spatially separated surface supercurrents confined to selected facets have not yet been achieved. Here we demonstrate facet-selective ballistic supercurrent in Josephson junctions based on the weak topological
insulator ZrTe<sub>5</sub>. Superconducting
quantum interferometry reveals SQUID-like critical current oscillations with flux-
quantum periodicity, establishing that the supercurrent is spatially concentrated on specific crystallographic facets that host gapless topological surface states. Rotating the
magnetic field yields markedly distinct interference patterns, linking the supercurrent distribution to the underlying bulk
topology. The exponential temperature dependence of the critical current and triangular interference lobes provide signatures of ballistic transport due to high-transmission topological channels. These results establish weak topological
insulators as a platform for facet-resolved superconducting devices and higher-order topological superconductivity.
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All authors Prasanna Rout, Ankit Khola, Lalit Pandey, Paolo Sessi, Xiaochun Huang, Ivo Cools, S. Galeski, Matthias Bode, Johan Åkerman, Floriana Lombardi, Thilo Bauch, Saroj P. Dash
Strongly Correlated Electrons
Quantum Oscillations of $\mathrm{Sr}_2\mathrm{RuO}_4$ under c-Axis Uniaxial Stress
Fabian Jerzembeck, Maximilian T. Pelly, Helge Rosner et al. (+7 more)
Uniaxial stress has now been widely used to study correlated electron materials. However,
Fermi surface-resolved experimental data on the
evolution of the electronic structure under piezoelectrically applied stress are sparse, with no reports of de Haas-van Alphen (dHvA) effects under uniaxial stress. Here we present dHvA measurements under $c$-axis uniaxial stress on the unconventional
superconductor $\mathrm{Sr}_2\mathrm{RuO}_4$. This allows us to study the
evolution of the electronic structure directly and to gain insight into the contradicting behavior of the predicted enhancement of the electronic density of states and the observed suppression of $T_\text{c}$. We are able to follow all
Fermi surfaces for stress up to $-1.8$~GPa and find that the cross-sectional areas of the hole-like $\alpha$ sheet increase and electron-like $\beta$ sheet decrease. At the same time, the area of the electron-like $\gamma$ sheet increases. Therefore, in contrast to in-plane uniaxial stress, charge transfer is the mechanism for approaching the electron-to-hole Lifshitz transition and the associated Van Hove singularity. Additionally, we find that the effective masses on all three
Fermi sheets are slightly enhanced as the Lifshitz transition is approached. We compare the dHvA results with
quantum oscillations in the magnetostriction and band structure calculations, and find good agreement. At a more general level, our findings show that
quantum oscillation measurements under uniaxial stress, combined with band-structure calculations, offer a promising new route for studying
quantum materials.
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All authors Fabian Jerzembeck, Maximilian T. Pelly, Helge Rosner, Edgar Abarca Morales, Naoki Kikugawa, Dmitry A. Sokolov, Andrew P. Mackenzie, Andreas W. Rost, Elena Hassinger, Javier F. Landaeta
Mesoscale and Nanoscale Physics
Spinterface-like mechanism of the chirality-induced spin selectivity in donor chiral-bridge acceptor complexes
Subhajit Sarkar, Oliver L. A. Monti and Yonatan Dubi
The chirality-induced
spin selectivity (CISS) effect has been invoked to explain recent reports of differences in the time-resolved EPR signals between
chiral and achiral molecules. However, the microscopic origin of these differences and their connection to CISS remains contested, particularly since these systems lack a metal interface. Here we introduce an intramolecular spinterface-like mechanism that naturally arises within donor-
chiral bridge-acceptor (D–$\chi$B–A) complexes and quantitatively reproduces experimentally reported observed
spin polarization in time-resolved EPR studies. In our two-electron Lindblad model, the photoexcited charge-transfer electron traversing the
chiral bridge exchanges with the residual donor electron, which acts as a localized
magnetic moment analogous to an induced
magnetic moment on an electrode surface. The resulting through-bridge charge current produces an effective solenoidal field at the donor–bridge interface, breaking
spin degeneracy and directional
symmetry, thus enabling
spin-selective transport without invoking intrinsic
spin-orbit coupling on the bridge. We show that the interplay between this current-induced field, donor thermalization (which breaks time-reversal
symmetry), and bridge
spin mixing yields tens-of-percent polarization over realistic experimental conditions and charge-transfer time scales, matching reported CISS signatures in triads and DNA hairpins. By explicitly resolving the dependence on solenoidal coupling strength, temperature, and
spin-mixing rates, the model identifies the regime in which internal spinterfaces can generate robust CISS-like
spin filtering. These findings demonstrate that CISS-like signals in isolated D–$\chi$B–A complexes are fully compatible with a spinterface mechanism, providing a unified conceptual framework for interpreting both device-based and molecule-internal CISS platforms.
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Superconductivity
Collective phase modes in twisted $d$-wave superconducting bilayers
Yin Shi, Mengxian Zhao, Fei Yang et al. (+2 more)
Twisted cuprate
bilayers have been predicted to host high-temperature
chiral $d+id'$ superconductivity, originating from higher-order Josephson coupling processes. In such two-dimensional superconducting systems, long-wavelength fluctuations in the phase of the superconducting order parameter constitute gapless collective modes and therefore remain significant even at zero temperature. Here, we perform a theoretical analysis of the low-energy phase fluctuations in twisted $d$-wave superconducting
bilayers within a self-consistent harmonic approximation, systematically retaining Josephson coupling to all orders. We demonstrate that higher-order Josephson coupling processes lead to nontrivial modifications of the phase dynamics. The momentum-resolved summand of the relative-phase stiffness is nonzero even in the normal state because interlayer tunneling explicitly breaks the intralayer U(1)
symmetry, but its momentum integral vanishes for the continuum dispersion. The relative-phase stiffness is smaller in the $d+id'$ phase than in the $d$-wave phase, while the overall-phase stiffness has the opposite behavior. Furthermore, phase fluctuations strongly soften the Josephson
plasma frequency near a twist angle of $45^\circ$ and also substantially reduce the Josephson critical current.
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All authors Yin Shi, Mengxian Zhao, Fei Yang, Miao Liu, Sheng Meng
Materials Science · Cross-listed from physics.optics
Self-selected phase-matched second harmonic generation in nonlinear optical materials: from phenomenon to applications
Niklas Dömer, Tobias Hehemann, Felix Sauerwein et al. (+3 more)
Self-selected phase-matched second harmonic generation is introduced as an all-optical probe of refractive-index dispersion in birefringent nonlinear optical materials. Rather than requiring wavelength or angular tuning, the exposure with a spectrally broad, intense ultrashort pulse allows the material to self-select the fundamental spectral component that satisfies the type-I noncritical phase-matching condition. This produces a narrow peak in the second harmonic spectrum whose position is governed by the refractive indices and is therefore highly sensitive to material parameters that affect the optical dispersion. We demonstrate the application of this phenomenon for the optical inspection of stoichiometry and temperature gradients in technologically relevant lithium niobate, as well as composition inhomogeneities in newly grown lithium niobate-tantalate solid solutions. These results establish self-selected phase-matched second harmonic generation as a rapid, non-contact method for inspecting nonlinear optical materials, with potential relevance for bulk
crystals, wafers, and thin-film platforms.
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All authors Niklas Dömer, Tobias Hehemann, Felix Sauerwein, Sebastian Inckemann, Steffen Ganschow, Mirco Imlau