Strongly Correlated Electrons
Unexpected stabilization of a single-$q$ charge density wave in pristine 1T-TiSe$_2$
Kimoon Higashihira Han, Dongju Hwang, Dongsin Kim et al. (+16 more)
Over the past decade, studies revisiting the classical charge-density-wave system 1T-TiSe$_2$, long understood to host the $2 \times 2$ triple-$q$ order with equivalent subcomponents, have suggested that these subcomponents may not be identical, challenging a 50-year-old paradigm. Here, we demonstrate not only that these subcomponents are non-identical but also that they develop sequentially rather than simultaneously. By tracking folded-band features, angle-resolved photoemission spectroscopy reveals that a unidirectional $2 \times 1$ single-$q$ order stabilizes first, while the other two components emerge sequentially at lower temperatures, completing the triple-$q$ phase. Our free-energy analysis explains this hierarchy through repulsive coupling among the three subcomponents, as supported by first-principles calculations incorporating
phonon anharmonicity. Consequently, the three subcomponents are inequivalent in both phase and amplitude. These results reconcile reported
symmetry breaking and differing characteristic temperatures and establish a framework in which ostensibly simple, high-
symmetry charge-density order emerges from temperature-dependent competition and cooperation among inequivalent subcomponents.
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All authors Kimoon Higashihira Han, Dongju Hwang, Dongsin Kim, Yeojin Ahn, Jaehun Cha, Seonggeon Gim, Gyubin Lee, Mingi Jho, Chan-young Lim, Sae Hee Ryu, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Jonathan D. Denlinger, Makoto Hashimoto, Donghui Lu, Young Woo Choi, Gil Young Cho, Yeongkwan Kim
Superconductivity
Quantitative Impact of Occupation Smearing Methods on Conventional Superconductivity: from Electronic Structure through Lattice Dynamics to Electron-Phonon Coupling
Zhongyu Wan
In first-principles calculations of metallic systems, the discrete electronic mesh in the Brillouin zone necessitates a smearing function and its width (e.g., the widely used 0.02 Ry Methfessel-Paxton scheme) to enforce continuity of energy and occupation at the Fermi surface. However, the quantitative impact of such empirical parameters on
phonon-mediated superconductivity has long been overlooked, leading to their habitual selection by mere convention. Here, using hexahydride CsH6 as a
benchmark, we systematically investigate the magnitude and propagation mechanism of smearing-induced errors against the parameter-free optimized tetrahedron method. Long-tailed smearing delocalizes the occupation window, causing substantial Fermi-level shifts, flattening of the density of states, and hardening
phonon modes, thereby weakening electron-
phonon coupling. Conversely, short-tailed smearing suffers from insufficient sampling, producing density-of-states oscillations and enhanced Fermi-surface nesting; via amplified electronic screening and Peierls instabilities, this softens acoustic modes and generates imaginary frequencies, causing CsH6 to be dynamically unstable and discarded. However, the optimized tetrahedron method reveals that CsH6 is dynamically stable under ambient pressure with a remarkable superconducting transition temperature of 121 K. To prevent subjective empirical parameters from obscuring theoretically promising high-temperature
superconductors, we derive a simple scaling relation for the smearing width, applicable to different smearing functions, from the free-electron-gas model, offering an objective, precise, and efficient protocol for parameter selection in high-throughput screening.
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Statistical Mechanics · Cross-listed from math.PR
Large deviations, gradient flows and fluctuating hydrodynamics for fractional diffusion
Julien Barre and Hiroshi Horii
This work is a step towards a general understanding of fluctuations for systems of particles described at large scale by fractional
diffusion. First, we derive formally a Large Deviation Principle for the empirical measure of mean-field interacting particles with a Lévy-type noise. In the case of independent particles, this unveils a generalized gradient flow structure at large scales. Second, we derive and solve numerically a
stochastic Partial Differential Equation describing the fluctuating hydrodynamics of this system. The results compare well with direct numerical integration of the particles' dynamics.
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Materials Science
Orientation-Resolved Nanoindentation of Single Crystal Ti-15Mo: Inverted Elastic Anisotropy and Yield-Onset Behavior Beyond Simple CRSS Predictions
Kidus Abebe, David Gaetano, Aurelia Moriyama-Gurish et al. (+4 more)
Ti-15Mo (wt%) is a well-established $\beta$-stabilized
alloy whose mechanical response is strongly governed by phase stability and deformation mechanisms that operate at the single-grain scale. Because these intragranular mechanisms are intrinsically anisotropic, understanding the orientation dependence of the elastic and plastic response is critical to the texture-engineered processing of wrought components. Here, we quantify the nanomechanical anisotropy of single-
crystal Ti-15Mo by combining EBSD with nanoindentation to correlate hardness, indentation modulus, strain rate sensitivity, and indentation yield response with the crystallographic surface normal near $\langle111\rangle,\langle124\rangle,\langle011\rangle,\langle023\rangle$, and $\langle013\rangle$ directions. While the modulus anisotropy is small (~10%), contrary to the prediction for a cubic
crystal with A>1, orientations near $\langle111\rangle$ exhibit the lowest moduli. Yield onset is likewise softest near $\langle111\rangle$ and spans 41%, while hardness spans only 6.6% and follows neither the modulus nor the yield ordering. The
alloy also exhibits yield behavior not captured by the simple CRSS/Schmid-factor models evaluated here. Strain-rate-jump tests yield V*=18-31b$^3$, consistent with kink-pair-nucleation-controlled plasticity; based on V*, the orientations separate into two groups suggestive of glide-dominated versus twin/transformation-participating response. We reveal an inversion of the elastic anisotropy expected for a homogeneous cubic $\beta$-phase and an orientation-dependent yield-onset response that is not reproduced by the simple Schmid-factor models examined here. Retained athermal $\omega$ is proposed as the contributor because $\beta\rightarrow\omega$ collapse occurs on {111}$_\beta$ planes and may provide anelastic compliance through the reversible $\omega\rightarrow\beta$ transformation.
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All authors Kidus Abebe, David Gaetano, Aurelia Moriyama-Gurish, Jana Šmilauerová, Yanfei Gao, Udo D. Schwarz, Amit Datye
Materials Science
High-throughput screening of Heusler alloys for thermoelectrics combining machine-learned densities of states and first-principles transport
Shivam Randive, Rahul Dixit and Himanshu Pandey
Thermoelectrics turn waste heat into electricity, but finding new ones requires transport calculations too costly for whole databases. Searches therefore choose what to calculate from the electronic density of states (DOS), increasingly predicted by machine learning, yet such choices are rarely tested. We test them on all 106,235 Heusler structures in the DXMag database, screening 51,257 on density-functional spectra and 54,978 on neural-network predictions, and judging both by 3,625 band-structure and transport calculations. A DOS-derived Seebeck indicator ranks most compounds passing every transport and stability test within the top 1% of their population, and ten of the eleven established half-Heusler thermoelectrics calculated pass. Predicted spectra lose most band gaps, unnoticed by spectral-similarity metrics, yet still rank passing compounds near the top. The screen certifies 80 computational candidates, 61 without reported measurements. Computed or predicted, the DOS can choose what to calculate; only a band structure shows whether a gap exists.
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Strongly Correlated Electrons
Non-Hermitian Statistical Geometry
Xi Hu, Yan-Qiong Ma and Su-Peng Kou
Particle exchange in two dimensions gives rise to
quantum statistics beyond the
boson-
fermion dichotomy, with central roles in fractional
quantum Hall physics, topological
quantum computation, and strongly correlated
quantum matter. In conventional topological phases, microscopic exchange geometry is compressed into rigid braid and fusion data. We develop a theory of non-Hermitian statistical geometry in which relaxing Hermiticity softens these exchange data into a larger complex space of spectral and relative-
geometric degrees of freedom. For two adjacent braid generators, a single projective exchange spectrum is insufficient: their relative eigenline geometry supplies an additional gauge-invariant modulus. On the generic irreducible two-channel branch, braid consistency locks these coordinates through an exact spectrum-geometry relation. Using Riesz projectors and Kato transport, we realize this geometry in a five-arm Kitaev-Majorana network and test spectral and relative-
geometric responses in an independent two-dimensional four-
vortex Kitaev model. Finite-time dynamics tests the exchange operation, microscopic fusion sewing tests its composition across fusion descriptions, and matched-spectrum controls isolate the role of relative geometry. Nonzero projective Kato
curvature shows that braid-consistent, fusion-coherent exchange can depend on the control path. Non-Hermiticity thus exposes exchange geometry, braid consistency re-locks it, fusion coherence further constrains it, and projective flatness determines when
geometric exchange becomes intrinsically topological.
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Superconductivity
Effects of the choice of the exchange-correlation functional on high-temperature superconductivity predictions in covalent-cage M(BN)5 family
Zhongyu Wan, Guo-Hua Zhong, Cheng-wei Ju et al. (+2 more)
The recent experimental synthesis of covalent cage
superconductors has ignited hopes for ambient-pressure high-temperature superconductivity, while the computational strategy for discovering new materials poses challenges for accurately estimating superconducting properties. Here, we quantified the response of electron-
phonon coupling (EPC) properties in M(BN)5
superconductors to different exchange-correlation (XC) effects using high-throughput first-principles calculations. We found that the metallic covalent bonds responsible for superconductivity exhibit anomalously high sensitivity to functional selection uncertainty, distinguishing them from conventional
superconductors mediated by metallic bonding. The widely used PBE functional systematically overestimates
lattice volumes, inducing
phonon softening, enhanced EPC, and consequent Peierls instability. In contrast, PBEsol, which is more accurate through enhanced treatment of short-range interactions, eliminates imaginary frequencies in Rb(BN)5 that appear at the PBE level, yielding an outstanding superconducting critical temperature (Tc) of 113 K at ambient pressure and 138 K at 2 GPa. Enhanced electron localization and short-range correlation in covalent bonds manifest through dual mechanisms:
phonon hardening at the
lattice scale and band widening at the electronic scale, which collectively suppress Peierls distortion and delocalize antibonding states. Pressure-dependent analysis reveals that compression attenuates
phonon discrepancies between XC functionals, whereas electronic properties remain notably sensitive to XC-induced perturbations of fine electronic bands near the Fermi level.
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All authors Zhongyu Wan, Guo-Hua Zhong, Cheng-wei Ju, Ruiqin Zhang, Hai-Qing Lin
Materials Science
Local-resolvent formulation and assessment of linear-scaling Kohn-Sham calculations
Albert Linda
Kohn-Sham density-functional theory is expensive because it needs orbitals that extend over the whole system. For
insulators this can be avoided by using only the diagonal of the one-electron resolvent, $g(\mathbf{r},z)=\langle\mathbf{r}|(z-\hat h)^{-1}|\mathbf{r}\rangle$, at a few complex energies $z$. We call the scheme local-resolvent density-functional theory (LRes-DFT). The density and the band energy are linear in $g$, so neither orbitals nor a kinetic-energy functional are needed. The complex energies are $M$ equally spaced points on a circle that encloses the occupied levels, offset by half a spacing so that no point lies on the real axis. Summing the resolvent over them is equivalent to occupying each level with $1/(1+u^M)$, where $u$ is the level's energy measured from the circle's center in units of its radius. This is a smooth step that is near 1 inside the circle and near 0 outside, and it stays between 0 and 1 for every $M$. If the circle moves with the chemical potential, forces at fixed electron number are exact. Gauss-Legendre and Zolotarev rules need fewer points when the gap is small. In three dimensions we use eigenpairs of small windows around each molecule instead of resolvents. This is divide-and-conquer (DC) with a different occupation function, and it is as accurate as DC with Fermi-Dirac occupations. For H$_2$ molecular
crystals of up to 1024 electrons it agrees with Kohn-Sham to $2.5\times10^{-7}$ Ha per electron. On one core it is slower than dense diagonalization below about 500 electrons and 3.5 times faster at 1024 electrons. It loses accuracy for disordered or compressed systems and for diffuse basis functions.
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Statistical Mechanics
Organisation and aggregation of calcium carbonate ions in water via molecular simulation
Elizaveta Sidler, Rita S Dias and Raffaela Cabriolu
Crystallisation of calcium carbonate (CaCO$_3$) in aqueous solutions is essential for carbon dioxide sequestration and the sustainable production of calcium carbonate materials, which are widely used in industry and increasingly explored for novel applications. While crystallisation is often analysed within the framework of classical nucleation theory, CaCO$_3$ and other ionic
crystals often form through amorphous precursor phases, motivating the need for alternative descriptions. In this work, we investigate the relationship between the formation of the first CaCO$_3$ coordination sphere, a fundamental unit of local ordering, and ionic aggregation using two complementary simulation approaches: on-the-fly probability-enhanced sampling (OPES) and asynchronous and infinite-swap replica exchange transition interface sampling ($\infty$RETIS). OPES was used to explore free-energy landscapes, whereas $\infty$RETIS was used to determine reaction kinetics. We studied systems at two levels of supersaturation, between which the formation of the first coordination sphere exhibited distinct kinetic behaviour. These differences were found to be linked to concentration-dependent ionic aggregation. At lower concentration, aggregation remains limited, whereas higher concentration promotes extensive spinodal-like aggregation. For both concentrations, the first coordination sphere forms within the pre-formed clusters through one of two distinct pathways: either within a cluster close to the minimum size required for its formation, or within larger amorphous aggregates whose size and structure depend on concentration. The coexistence of these pathways at both levels of supersaturation reveals the multifaceted nature of early-stage CaCO$_3$ crystallisation and highlights the importance of differentiating ionic aggregation and organisation.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Local error correction prolongs time-crystalline memory
Benedikt Fauseweh
Discrete time
crystals are non-
equilibrium phases of matter with spatiotemporal order and a response that breaks the time-translation
symmetry of a periodic external drive. Interactions, spatial disorder and correlated random driving can in theory stabilize this order. In experiments, however, coupling to the environment limits the time
crystal lifetime. Here we use
stochastic local bit-flip error correction to prolong the time-crystalline response of a driven, spatially disordered two-dimensional Ising model on a superconducting
quantum processor, using a repetition code with distances three and five on a honeycomb
lattice with up to 68 physical
qubits. Even though ancilla
qubits, midcircuit syndrome measurements and decoding increase the required
quantum and classical resources, the
stochastic drive increases the
memory decay time by a factor of up to two. At late times we observe that recovery stabilizes spatial order across the
lattice. The
spin-configuration distributions explain this separation, as recovery suppresses disagreeing bonds while broadening occupies completely reversed states. Syndrome measurements without correction accelerate the
memory decay, demonstrating the importance of conditional correction. Our results show that local bit-flip error correction can preserve time-crystalline
memory over more drive cycles than the bare dynamics.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Chirality Inversion and Giant Optical Activity in Scalable Self-Assembled Metamaterials
Antonio Carone, Aso Rahimzadegan, Birgül Kalkan et al. (+8 more)
Chiral materials manipulate light in ways that hold promise for sensing, imaging, and photonics, but producing such materials with strong and reproducible optical activity at large scale remains challenging. Here, we develop a scalable strategy to assemble hierarchical helicoidal metamaterials from metallic nanoparticles and chitin nanocrystals, a biosourced polysaccharide. Spontaneous co-assembly produces ordered chiral structures with strong plasmonic optical activity, reaching a dissymmetry factor of 0.55. The unprecedented ability to vary the helicoidal pitch allows control of the optical response, enabling inversion of optical handedness without changing the handedness of the template, effectively decoupling geometrical chirality from optical chirality. Remarkably, the gold nanoparticles can also be recovered from dry films and redispersed as colloids, introducing an appealing circularity concept for sustainable chiral plasmonic materials.
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All authors Antonio Carone, Aso Rahimzadegan, Birgül Kalkan, Thomas G. Parton, Tony Jin, Zihao Lu, Clemens Schmitt, Emeline Raguin, Bruno Frka-Petesic, Kevin Vynck, Silvia Vignolini
Disordered Systems and Neural Networks · Cross-listed from hep-th
Supersymmetric Observables from Surface Defect Anomalies in 4d and 6d SCFTs
Zi-Xiao Huang, Ma-Ke Yuan and Yang Zhou
We study the contributions of half-BPS surface defects to supersymmetric Casimir energy and the universal logarithmic term of supersymmetric Rényi
entropy in four- and six-dimensional SCFTs. Using equivariant integration of defect anomaly
polynomials and its extension to supersymmetric Rényi backgrounds, we obtain closed expressions for these observables in terms of defect 't Hooft anomalies. For Gukov–Witten defects preserving transverse rotations in four-dimensional $\mathcal{N} = 4$ super Yang–Mills theories, both observables depend on a single R-
symmetry anomaly. For $\mathcal{N} = (0, 4)$ defects in six-dimensional $\mathcal{N} = (1, 0)$ theories, additional terms arise from the gravitational anomaly. We provide complementary checks using chiral
algebras, five-dimensional localization, and holographic probe branes at large $N$, while localized chiral
fermions reproduce the gravitational-anomaly contributions. The framework also recovers Wilson-surface results in six-dimensional $\mathcal{N} = (2, 0)$ theories.
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Materials Science
Tellurium trioxide as an n-type wide-gap semiconductor with ultrahigh work functions from first principles
Tianwei Wang, Teruya Nagafuji, Kota Hanzawa et al. (+2 more)
The exploration of next-generation wide-gap
semiconductors with extreme work functions is highly desirable for the continued advancement of electronic and optoelectronic devices. By using first principles calculations, we show that e̱ta}-TeO3, with a wide band gap exceeding 3 eV, emerges as a promising n-type
semiconductor exhibiting ultrahigh work functions of up to ~8 eV. Intentionally or unintentionally incorporated interstitial H, Li, Na, Cu, Mg, and Zn impurities and substitutional F impurities are identified as shallow donors, whereas O vacancies act as minor carrier-compensating defects that locally trap electrons at neighbouring Te sites. The work function is evaluated across a series of low-index nonpolar surfaces. The presence of ordered O vacancies is energetically favoured on these surfaces and tends to reduce the corresponding work functions. These findings underscore the significance of precise control over the O chemical potential to suppress surface O-vacancy formation, thereby preserving the exceptional electronic performance of e̱ta}-TeO3 associated with ultrahigh work functions. Collectively, the results highlight the potential of e̱ta}-TeO3 for hole injection/extraction/transport layers as well as transparent electrodes for applications such as light-emitting devices and photovoltaic
cells, while providing useful guidance on carrier doping and surface tuning for these practical applications through elucidating the effects of the point-defect and surface configurations on the electronic properties.
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All authors Tianwei Wang, Teruya Nagafuji, Kota Hanzawa, Hidenori Hiramatsu, Fumiyasu Oba
Soft Condensed Matter
Evolution of dense liquid marbles under light tapping
Amaelle Sprocq, Théo Dhoudain, Alexis Duchesne et al. (+1 more)
Liquid marbles interface is composed by a dense network of grains trapped by capillarity at their surface. The mix of capillarity and granular character make their interfaces remarkable, allowing non wetting, high mobility and strong robustness which are a basis for numerous applications. A canonical experiment showing out of
equilibrium nature of granular material is the so called tapping experiment, where a dry granular medium under vertical vibration reorganize an evolve toward a denser final state function of the vibration amplitude In this paper we explore the out of
equilibrium nature of densely covered
liquid marbles by measuring their shape, compaction and stresses
evolution under vertical vibration. We show that
liquid marble do indeed reorganize when submitted to taps, leading to higher internal pressure and lower effective surface tension.
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All authors Amaelle Sprocq, Théo Dhoudain, Alexis Duchesne, Guillaume Lagubeau
Materials Science
Hydrogen partial pressure as a key parameter in the reactive sputtering of photochromic YHO thin films
E. Strods, M. Zubkins, E. Letko et al. (+3 more)
Oxygen-containing yttrium hydride (YHO) thin films were synthesised by reactive magnetron sputtering over a wide range of hydrogen-to-argon gas flow ratios (H2/Ar) during yttrium hydride deposition, followed by post-oxidation in air. The deposition process was monitored in situ by
plasma optical emission spectroscopy. X-ray diffraction reveals a strong dependence of crystallographic texture on the H2/Ar ratio: highly <100>-textured films formed at low H2/Ar ratios progressively evolve into more polycrystalline microstructures with slightly reduced crystallite size as the hydrogen content increases. The optical transmittance gradually decreases from approximately 85 % to 70 % as the H2/Ar ratio is raised to 0.6, followed by a sharp drop at higher hydrogen contents. The photochromic contrast of 705-845 nm thick YHO films, measured after 10 min of illumination with a solar simulator, decreases from 14 % to 7 % as the H2/Ar ratio increases from 0.08 to 0.45. Thinner films (365-505 nm) exhibit a similar but less pronounced trend. Bleaching kinetics, analysed using a double-exponential model, indicate faster recovery, with effective bleaching time constants of approximately 1-15 min for films deposited at H2/Ar < 0.25. X-ray photoelectron spectroscopy reveals higher oxygen incorporation in films deposited at lower H2/Ar ratios, deviating from the commonly reported correlation between oxygen content and photochromic response in YHO. These results demonstrate that low hydrogen partial pressure during reactive sputtering is advantageous for achieving higher optical transparency, enhanced photochromic contrast, and faster bleaching kinetics in YHO thin films.
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All authors E. Strods, M. Zubkins, E. Letko, V. Vibornijs, A. Sarakovskis, J. Purans
Materials Science
Knowledge-Guided Construction of Machine Learning Potentials for Reactive Behavior in Energetic Materials
Guanchen Dong, Huanrong Liu, Lin Wang et al. (+12 more)
Energetic materials involve multiple interactions, making reliable machine-learning potentials (MLPs) difficult to construct without extensive
datasets. Here, we enhance the ability of the neural network interatomic potential (NNAP) to describe molecular systems using sphmulti, a refined spherical-harmonic basis set that combines extra radial basis with element-specific chemical weighting in each radial channel. We further integrate hyperactive learning, farthest-point sampling, and iterative sufficiency criteria with knowledge-guided key events, enabling the NNAP to retain essential information for describing the material system. For 3,3'-diamino-4,4'-azoxyfurazan, the resulting NNAP is trained on only 13,680 configurations yet captures key properties, including the isomerization barrier, pyrolysis activation energy, and shock Hugoniot behavior. NNAP-driven molecular dynamics simulations further reveal that pyrolysis proceeds through furazan-ring opening followed by chain reactions, whereas shock loading induces anisotropic hydrogen transfer driven by interlayer structural deformations. This work enables efficient and reliable MLPs for energetic materials.
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All authors Guanchen Dong, Huanrong Liu, Lin Wang, Yuxuan Chen, Zhengyu Tu, Qing-an Li, Bin Xu, Jian Li, Shan Zhang, Xiaotong Li, Linghua Tan, Guangcheng Yang, Jun Kang, Rui Su, Pengfei Guan
Strongly Correlated Electrons
Direct view of exciton and carrier dynamics in twisted bilayer graphene
Gianmarco Gatti, Anders S. Mortensen, Zhihao Jiang et al. (+12 more)
Twisted bilayer
graphene (tBLG) on H-intercalated SiC (twist angle of $9 \pm 1^{\circ}$) is studied by position\mbox{-}, time\mbox{-}, and angle-resolved photoemission spectroscopy (ARPES). Both
graphene layers are hole doped, with a Dirac-point offset of 30~meV. Time-resolved ARPES near the van Hove singularity reveals a spectral feature within the hybridization-induced band gap, together with excited electrons in the conduction band. The in-gap feature exhibits distinct dynamics, and its binding energy and $k$-space location are consistent with the proposed non-hydrogenic “ghost-Fano”
exciton arising from destructive interference between two nearly degenerate excitonic channels. Near the Dirac points, the twist separates the largely layer-polarized Dirac cones in momentum space, providing direct layer selectivity. We find markedly different peak electronic temperatures in the two
graphene layers, even though their subsequent cooling dynamics are very similar. We attribute this to an ultrafast interlayer redistribution of electronic energy, driven by an interlayer electric field that arises from the different doping in the layers.
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All authors Gianmarco Gatti, Anders S. Mortensen, Zhihao Jiang, Alfred J. H. Jones, Gesa-R. Siemann, Thomas S. Nielsen, Søren Ulstrup, Naina Kushwaha, Bruce Weaver, Yu Zhang, Emma Springate, Charlotte E. Sanders, Vibha Reddy, Ulrich Starke, Philip Hofmann
Materials Science
Field-free Magnetoacoustic Nonreciprocity via Exchange-bias Engineering
Weiqi Du, Mingyuan Ma, Zheng Sun et al. (+8 more)
Nonreciprocal wave propagation is essential for directional signal processing and isolation. Magnetoacoustic systems are attractive platforms for nonreciprocal devices because of their small footprint and passive operation. However, pronounced nonreciprocity typically requires an external bias field,limiting device miniaturization and integration. Here, we demonstrate field-free magnetoacoustic nonreciprocity in an IrMn/FeGaB/Cu/FeGaB multilayer integrated with a shear-horizontal-wave delay line. Exchange-bias engineering stabilizes a remanent
magnetic state with broken time-reversal and spatial-inversion
symmetries while tailoring the
spin-wave dispersion to achieve resonant magnetoacoustic coupling at zero field. The normalized isolation reaches 21 dB/mm, with its sign programmable by the field-sweep history. Further numerical optimization predicts a zero-field normalized isolation of 91 dB/mm by increasing the dynamical
magnetic asymmetry. Our work establishes exchange-bias engineering as a promising route toward compact RF isolators and circulators and as a general strategy for realizing magnetoacoustic devices without external
magnetic fields.
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All authors Weiqi Du, Mingyuan Ma, Zheng Sun, Chong Chen, Shixuan Liang, Deqi Tao, Shihai An, Yifan Fu, Sulei Fu, Feng Pan, Cheng Song
Materials Science · Cross-listed from physics.chem-ph
All-electron machine-learned orbital-free density functional for periodic CHNO systems
Marc K. Ickler, Andreas Hermann and Fred A. Hamprecht
We introduce STRUCTURES-P, a machine-learned all-electron orbital-free density functional for periodic CHNO systems. Electrostatics are evaluated analytically in an atom-centered Gaussian basis, while an equivariant network learns the kinetic and exchange-correlation energy from energies and gradients of non-ground-state densities. Minimizing the functional from a superposition of atomic densities recovers the Kohn-Sham ground state: on held-out
crystals, the density error falls from 6.7% to 0.4% of the electron count and the energy error reaches 0.25 mHa per atom, half that of a same-architecture interatomic potential. A single functional can be trained for both isolated molecules and periodic systems, and the model generalizes to larger unit
cells. It largely preserves relative-energy rankings and reproduces convex-hull vertices on the tested H-N composition slice. Together, these results demonstrate the viability of machine-learned all-electron orbital-free DFT for variational density optimization and energy evaluation in fixed-geometry solids.
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Materials Science
Thermal stability and structural ordering of thick Co$_2$MnAl films grown on MgO and Si substrates
David Robles-Cuenca, Juan Antonio González, Juan Pedro Andrés et al. (+3 more)
While most studies on Co$2$MnAl (CMA) focus on the ultrathin regime for spintronic junctions, applications scaling with
magnetic volume–such as Anomalous Nernst Effect (ANE) energy harvesters, integrated power inductors, and
magnetic MEMS–require significantly thicker films. In this work, 750 nm thick CMA films were grown on MgO (001) and Si substrates to establish a roadmap for their thermal integration. Structural analysis reveals that B2 ordering is optimized on MgO at 600 $^\circ$C, which is important for functional devices. In contrast, samples on Si substrates exhibit a disorder transition toward the A2 phase, closely linked to
diffusion-driven degradation processes. Above 500 $^\circ$C, Si interdiffusion into the Heusler layer triggers the formation of interfacial silicides and Kirkendall voids, leading to microcracking, electrical resistivity jumps, and a final fully disordered A2 phase. Despite the Mn-poor stoichiometry (Co$2.25$Mn$0.7$Al$1.05$), the films maintain a robust saturation magnetization of ~600 emu/cm$^3$, consistent with recent theoretical models for off-stoichiometric Heusler
alloys. These results define the processing windows for integrating thick CMA layers into multifunctional CMOS-compatible platforms.
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All authors David Robles-Cuenca, Juan Antonio González, Juan Pedro Andrés, Miguel Ángel Arranz, Mohamed Salaheldeen, Ricardo López Antón
Mesoscale and Nanoscale Physics
WannierSTM: Efficient superconducting scanning-probe spectroscopy from maximally localized Wannier functions
Oscar Moreno Segura, Dorye L. Esteras, Andrei Shumilin et al. (+3 more)
We present a Python-based program that combines maximally localized Wannier functions-based first-principles electronic structure with the nonequilibrium Green's function formalism to enable efficient simulations of scanning tunneling microscopy (STM). The workflow builds upon standard density functional theory packages to construct compact transport
Hamiltonians that preserve the properties of realistic materials. Superconductivity is incorporated via an effective pairing potential within the Nambu-spinor formalism, while coupling to the STM tip and substrate electrodes is treated using the wide-band limit approximation. Within this formulation, transport quantities such as current-voltage characteristics and differential conductance are evaluated in a closed analytical form. This avoids explicit numerical energy integrations and enables rapid spectroscopic calculations over broad parameter spaces. The framework provides a unified and computationally efficient approach for modeling superconducting hybrid nanostructures with
spin-orbit coupling,
magnetic textures, and
spin polarization. Representative applications in
spin chains, two-dimensional and molecular magnets on a
superconductor demonstrate its robust capabilities for both simple model systems and realistic ab initio molecular structures relevant to modern STM experiments.
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All authors Oscar Moreno Segura, Dorye L. Esteras, Andrei Shumilin, Gonzalo Rivero-Carracedo, Riku Tuovinen, José J. Baldoví
Strongly Correlated Electrons
Conformal soft modes at elastic instabilities
Lars Franke, Nick Sander and Markus Garst
In case a
crystal is close to a continuous elastic phase transition, pronounced critical fluctuations emerge. We show that on the level of linear elasticity theory the displacement vector for these critical modes obeys a condition reminiscent of the conformal Killing equation. For an isostructural instability, four critical modes arise corresponding to one dilation and three special conformal transformations. At
crystal symmetry-breaking instabilities, the critical fluctuations include a continuum of modes even for
crystals with finite size. For certain cases, these comprise the conformal transformations associated with two-dimensional Minkowski space. These results have implications for critical elastic phenomena as well as for extremal mechanical metamaterials.
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Statistical Mechanics · Cross-listed from cs.LG
Deep Mesoscopic Dynamics
Yue Zhao, Shiqi Wu, Yihang Ouyang et al. (+6 more)
Microscopic simulations resolve spatial patterns but are feasible only over small domains and short timescales, whereas bulk descriptions erase those patterns through spatial averaging. Mesoscopic fields preserve this spatial organisation, but their effective equations are known only for selected microscopic systems and scaling limits. We introduce Deep Mesoscopic Dynamics (DeepMesoD), which uses neural networks to learn an effective mesoscopic field equation from microscopic trajectories at a prescribed coarse-graining scale. For the nonconserved dissipative dynamics studied here, DeepMesoD learns the free-energy functional with a spatial interaction kernel and a state-dependent dissipation operator constrained by the fluctuation-dissipation relation. We first validate the construction in the Ising-Kac model, where the learned mesoscopic equation recovers the known hydrodynamic limit and rollouts remain stable far beyond the training horizon. We then treat two systems without closed-form mesoscopic descriptions. For a two-dimensional Heisenberg ferromagnet governed by atomistic
spin dynamics, DeepMesoD learns a mesoscopic model whose predictions match atomistic references up to 1 ns, and a rollout with an unseen initial condition remains bounded up to 25 ns. For layered CrBr$_3$, the learned kernel captures the suppression and sign reversal of interlayer coupling at a stacking fault whose location and strength are not supplied as inputs. Controlled changes to the learned interaction show how fault number and placement shape multistep
magnetic responses, complementing our magneto-photoluminescence measurements. Across the two atomistic systems, DeepMesoD achieves a three-to-four-order-of-magnitude reduction in wall-clock time compared with atomistic
spin dynamics.
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All authors Yue Zhao, Shiqi Wu, Yihang Ouyang, Sergey Grebenchuk, Magdalena Grzeszczyk, Xiaoxu Zhao, Kostya S. Novoselov, Maciej Koperski, Qianxiao Li
Superconductivity
Imaging atomic-scale surface structure and superconducting gap of the misfit layered compound (SnS)1.17NbS2
Dongming Zhao, Shamarita Deb, Lichen Ji et al. (+8 more)
Superlattices of van der Waals-coupled two-dimensional materials offer a platform for engineering electronic band structure and fostering emergent
quantum states. Misfit layered compounds provide naturally assembled superlattices, in which crystallographically distinct two-dimensional subsystems coexist within a single bulk
crystal. Therein, the presence of both commensurate and incommensurate
lattice directions introduces structural modulation, which might alter real-space electronic orders such as superconductivity. Here, we investigate the atomic-scale surface structure and local superconductivity of the misfit layered compound (SnS)1.17NbS2 using structural characterization, electrical transport, and low-temperature scanning tunnelling microscopy (STM). While X-ray diffraction and cross-sectional scanning transmission electron microscopy confirm the bulk misfit structure, STM resolves large SnS- and NbS2-terminated terraces, where the surface atomic registry differs from the bulk misfit structure. Furthermore, tunnelling spectroscopy at 2 K reveals nearly identical superconducting gaps on both terminations, and the spatial variation of the gap shows no visible modulation that corresponds to the misfit
lattice. These results establish an atomic-scale picture of the surface structure and superconducting states of this naturally assembled misfit
heterostructure.
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All authors Dongming Zhao, Shamarita Deb, Lichen Ji, Souvik Das, Paul Simon, Raúl Cardoso-Gil, Steffen Wirth, Walter Schnelle, Sushmita Chandra, Jian-Feng Ge, Claudia Felser
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
On-chip optical isolators
Abanoub Mikhail, Nikolay Solodovchenko, Sen Xu et al. (+5 more)
Optical isolation suppresses back-reflections that destabilize
lasers, produce parasitic interference, and increase crosstalk in photonic systems. Although free-space and fibre-optic isolators are mature, no broadly adopted on-chip technology yet combines strong isolation, low insertion loss, broad bandwidth, compact footprint, and scalable fabrication. The difficulty is twofold: Lorentz reciprocity must be broken, and every relevant backward spatial, spectral, and polarization channel must be suppressed. This Review develops a common framework for assessing proposed solutions. We first distinguish pairwise nonreciprocity from intensity-asymmetric transmission and from true isolation using the constitutive relations and scattering
matrix. We then compare three physical routes to an integrated nonreciprocal response: magneto-optical bias, externally driven space-time modulation, and nonlinear optical processes. Topological and non-Hermitian systems are treated as cross-cutting design frameworks that can route, protect, or enhance an underlying nonreciprocal response, but do not by themselves break reciprocity. Finally, we examine fundamental constraints and practical trade-offs among isolation, insertion loss, bandwidth, footprint, modal coverage, drive requirements, and fabrication compatibility. The resulting mechanism-based perspective connects reciprocity-breaking physics to the requirements of scalable photonic integrated
circuits.
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All authors Abanoub Mikhail, Nikolay Solodovchenko, Sen Xu, Fan Zhang, Maksim Tumashov, Mingzhao Song, Sergei Makarov, Andrey Bogdanov
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Emergent Non-Biorthogonal Born Rule at Dynamical Quantum Phase Transitions
Wei-Wei Yang, Henning Schomerus, Jiangping Hu et al. (+1 more)
Non-Hermitian dynamics possesses distinct left and right eigenstates, but their normalization freedom obscures a direct probabilistic interpretation. Starting from a globally Hermitian system governed by the standard Born rule, we generalize dynamical
quantum phase transitions (DQPTs) from a reference state to a physical subspace. This generalization provides a clear probabilistic interpretation of left and right states: when each state is normalized to itself, their mutual overlap determines a directly accessible dynamical transition rate. We discuss the new phenomena governed by this emergent non-biorthogonal Born rule and further identify a class of exceptional-point DQPTs (EP-DQPTs), at which the eigenstates of the critical propagator coalesce. Our theory places the probabilistic interpretation of non-Hermitian
quantum mechanics on the firm footing of Hermitian
quantum mechanics.
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All authors Wei-Wei Yang, Henning Schomerus, Jiangping Hu, Zhesen Yang
Materials Science
ARES: a plane-wave density-functional-theory code in Rust
Zehan Liu, Qian Wang, Xiangyu Zheng et al. (+7 more)
ARES (Ab initio atomic mateRial modEling Software at JLU) is a plane-wave density-functional-theory (DFT) code written entirely in Rust as a layered 22-crate workspace. It supports norm-conserving pseudopotentials and the projector augmented-wave (PAW) method with the local-density approximation (LDA) and Perdew-Burke-Ernzerhof (PBE) functionals, {\Gamma}-only and explicit k-point sampling, smearing and mixing, forces, stress, relaxation, band structures, densities of states (DOS) and dispersion corrections; execution is serial or MPI-distributed over k-point pools, band groups and plane-wave rows. The code's distinguishing engineering choice is its validation apparatus. Every numerical component is checked against
Quantum ESPRESSO driven from the same physical and numerical inputs, and the comparison is organized as numbered fixtures kept in the repository whose reference data is regenerated by a script instead of being captured once. On six materials spanning a
semiconductor, three metals and two two-dimensional systems, band energies within one electronvolt of the Fermi level agree with the reference to a median below 0.4 meV. The pseudopotentials the code reads are validated against all-electron reference data as well: the median delta factor is 0.696 meV/atom over all 65 paired elements. Restrictions are stated with the capabilities: two functionals, no
spin-polarized or
spin-orbit path, a stress implementation with an explicit scope, and no accelerator execution.
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All authors Zehan Liu, Qian Wang, Xiangyu Zheng, Jiaxiang Li, Chuntian Wu, Yongshuo Chen, Xuecheng Shao, Qiang Xu, Yu Xie, Yanming Ma
Materials Science
Colossal Spin–Lattice–Charge Coupling in Noncollinear Ferrimagnetic NbMnX$_2$ ($X$ = S, Se, Te) Monolayers
Peng Wang, Nanshu Liu, Hongkuan Yuan et al. (+2 more)
Noncollinear ferrimagnets combine a net
magnetic moment with internal
spin degrees of freedom, creating opportunities to couple
magnetic, mechanical, thermal, and electronic responses. Using first-principles calculations,
symmetry analysis, atomistic
spin simulations, and transport modeling, we identify stable NbMnX$_2$ ($X$ = S, Se, Te) monolayers with noncollinear ferrimagnetic ground states and Curie temperatures up to 313 K. Competing exchange, Dzyaloshinskii–Moriya interactions, and
magnetic anisotropy produce field-responsive canted states that couple strongly to the
lattice and charge carriers. Magnetization rotation changes the elastic modulus of NbMnTe$_2$ by up to 36%, while
lattice entropy substantially enhances the near-room-temperature magnetocaloric response of NbMnS$_2$ and NbMnSe$_2$. In NbMnSe$_2$, rotation restores a mirror-protected crossing, continuously closes an approximately 0.13 eV gap, and produces a conductivity-based anisotropic magnetoresistance ratio up to 10,000% at 100 K. The combined results establish noncollinear NbMnX$_2$ monolayers as a multifunctional platform for two-dimensional spintronics, nanomechanics, and thermal control.
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All authors Peng Wang, Nanshu Liu, Hongkuan Yuan, Xue Jiang, Jijun Zhao
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Theory of deeply subwavelength electromagnetic structuring of semiconductors due to thermal-ionization instability
I. V. Oladyshkin, D. I. Kulshin and E. O. Smolina
We develop a theory of ionization-assisted instability that governs the reflection of intense electromagnetic pulses from a
semiconductor surface. Local overheating of the material increases the free-carrier density and conductivity, which in turn enhances the absorption of the incident radiation and further amplifies local heating and avalanche ionization. At high pump repetition rates, the overheating accumulates from pulse to pulse, leading to a gradual rise of the local material temperature and free carrier density - a positive feedback loop that drives thermal runaway. However, this effect competes with diffraction of the pump field on the emerging perturbation of the dielectric permittivity or on the surface relief, which reduces the local electric field amplitude in the overheated regions, thus providing negative feedback. We show that the competition between heat
diffusion and diffraction near-field weakening creates conditions for the exponential growth of temperature perturbations with a certain wavenumber determined by the pulse repetition rate, pump field, thermal conductivity and other material parameters. The derived analytical expressions accurately describe the spatial period of deeply subwavelength structures observed in recent experiments on silicon structuring by intense terahertz radiation, and reproduce qualitatively dependencies of their period on the pump intensity, the incident wavelength and the number of pump pulses.
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Materials Science
Orthoexciton-to-paraexciton conversion rate in Cu$_2$O at sub-Kelvin temperatures
Yusuke Morita, Yukihiro Akiyama, Yuki Haita et al. (+2 more)
We measured the conversion rate from 1s orthoexcitons to 1s paraexcitons in Cu$_2$O below 1 K using a dilution refrigerator. To determine the conversion rate, we performed time-resolved luminescence spectroscopy of 1s orthoexcitons and 1s paraexcitons confined in a strain-induced trap potential. From the time
evolution of the ${\Gamma}$$_3$$^{-}$-LO-
phonon-assisted luminescence of 1s orthoexcitons, we obtained a conversion rate of $5.9 \times 10^7$ s${^{-1}}$ at a mixing-chamber temperature of 64 mK under an applied stress of 2.2 kbar. Between 64 and 800 mK, the conversion rate depends only weakly on temperature, and it is less than half of the value of $1.6 \times 10^8$ s${^{-1}}$ reported at 2 K under the same applied stress. The conversion rate therefore continues to decrease below 2 K, contrary to the previous expectation that it becomes nearly constant below about 1.7 K. We discuss these results in terms of the momentum distribution of orthoexcitons, which does not reach
equilibrium with the
lattice during the conversion at these low temperatures. These findings call for a theory that accounts for both the small magnitude of the conversion rate and its weak temperature dependence below 1 K.
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All authors Yusuke Morita, Yukihiro Akiyama, Yuki Haita, Yuga Hirota, Kosuke Yoshioka