Materials Science
Decoupling Strain-Rate Sensitivity and Deformation Length Scale Effects in Neutron-Irradiated Tungsten: A Coupled Nano-Indentation, HR-EBSD and Crystal Plasticity Study
Prashil S. Joshi, Bethany Jim, Chris Hardie et al. (+3 more)
Plastic deformation during strain-rate-controlled spherical nanoindentation is governed by the coupled
evolution of constitutive strain-rate sensitivity and deformation length scale, making the intrinsic influence of strain rate difficult to isolate experimentally. This coupling is investigated in unirradiated and
neutron-irradiated single-
crystal tungsten using spherical nanoindentation, atomic force microscopy, high-resolution electron backscatter diffraction (HR-EBSD), and
crystal plasticity finite element (CPFE) modeling. Nanoindentation experiments were performed at strain rates from 3.2e-5 to 3.2e-3 per second. AFM and HR-EBSD quantified surface pile-up, residual
lattice strain, and geometrically necessary dislocation (GND) distributions. A strain-gradient CPFE framework incorporating thermally activated slip, GND hardening, irradiation-induced obstacle hardening, and strain-dependent softening was calibrated using a single experimental condition and validated across all remaining strain rates without further parameter adjustment. The validated model was then used to independently vary strain rate and indentation depth. Simulations show that strain rate primarily controls the stress required for thermally activated plastic flow, whereas indentation depth governs plastic-zone
evolution, pile-up, and GND accumulation. Irradiation increases obstacle strength and promotes deformation localization while remaining consistent with a common thermally activated mechanism. The framework also predicts the compression response of a polycrystalline cube, demonstrating transferability across loading conditions and length scales, providing a robust basis for constitutive modeling of irradiation-hardened materials under transient loading.
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All authors Prashil S. Joshi, Bethany Jim, Chris Hardie, Angus Wilkinson, David EJ Armstrong, Suchandrima Das
Statistical Mechanics
Optimal preparation and reachable-state constraints in the Mpemba effect
C. Ríos-Monje, A. Patrón-Castro, C. A. Plata et al. (+2 more)
The Mpemba effect, whereby an initially hotter system relaxes faster than a colder one towards a common final state, is often analysed within the kinetic framework by assuming non-stationary initial conditions that are selected a priori. Here, we revisit this viewpoint by explicitly incorporating the aging protocol used to prepare those states. Focusing on uniformly heated granular fluids, we formulate the preparation stage as an optimal-control problem in which the energy injection is tuned to generate the initial conditions that maximise or minimise the subsequent relaxation rate. Within the first Sonine approximation, this optimisation reduces to extremising the excess kurtosis of the velocity distribution function, the quantity controlling the cooling rate at fixed temperature. Applying Pontryagin's maximum principle, we show that the optimal preparation protocol is always a one-bang protocol and determine the corresponding extremal values of the excess kurtosis. Most importantly, we find that the
stochastic thermostat imposes non-trivial reachable-state constraints: the accessible non-Gaussianities are bounded by those of the homogeneous cooling state, thereby limiting the relaxation-rate asymmetry and the maximum attainable Mpemba effect. These results demonstrate that the strength of the kinetic Mpemba effect cannot be disentangled from the accessibility of the underlying non-
equilibrium states. More generally, our work establishes a connection between anomalous relaxation, optimal control, and state accessibility in non-
equilibrium systems.
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All authors C. Ríos-Monje, A. Patrón-Castro, C. A. Plata, B. Sánchez-Rey, A. Prados
Statistical Mechanics
Coherent Bose-Einstein condensation with fluctuating density
L. Salasnich, A. Crisanti, A. Sarracino et al. (+1 more)
Bose-Einstein condensation in the grand canonical ensemble admits a formulation in terms of a phase-density decomposition of the condensate mode operator $\hat{\psi}_{\bf 0}$. In the presence of macroscopic condensate number fluctuations this representation presents nontrivial implications. In particular, we show that, for the ideal gas, under the assumption of a well-defined phase and a fluctuating condensate density, the square modulus of the anomalous average $\langle \hat{\psi}_{\bf 0}\rangle$ can provide only a fraction of the whole condensate density $\rho_{\bf 0}$ and for the grand canonical statistics of the ideal Bose gas one obtains the value $|\langle {\hat \psi}_{\bf 0}\rangle|^2 =(\pi/4) \rho_{\bf 0}$. The remaining part is supplemented by the (macroscopic) fluctuations of $\hat{\psi}_{\bf 0}$, which become a distinctive feature of the BEC in this setting. This provides a transparent physical picture of a condensate of
photons with a well-defined phase but large number fluctuations, as observed in dye-filled microcavity
photon experiments. We also propose a way to access the square modulus of the anomalous average to test theoretical predictions.
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All authors L. Salasnich, A. Crisanti, A. Sarracino, M. Zannetti
Strongly Correlated Electrons
Microscopic Spin-1 Parent Hamiltonians for Emergent Valence-Bond Loop Manifolds
Hari Borutta, Yasir Iqbal and Kirill Shtengel
We construct an exact
spin-$1$ parent
Hamiltonian for constrained valence-bond loop
manifolds on the checkerboard and pyrochlore
lattices. The
Hamiltonian is local, SU(2)- and time-reversal-invariant, and built from positive-semidefinite projectors acting on triangular faces. Each projector removes only the maximally polarized state of a triangle, so the model is frustration-free. Its zero-energy states are generated by an AKLT-like construction in which each
spin-$1$ moment is resolved into two virtual
spin-$\tfrac12$ degrees of freedom, singlets are formed inside every crossed plaquette or tetrahedron, and the physical
spin-$1$
Hilbert space is recovered by projection. The resulting ground states are fully packed singlet-loop states on the corner-sharing
lattice. Thus, a loop or dimer constraint, usually introduced as part of an effective Rokhsar–Kivelson description, appears here as the exact zero-energy
manifold of a microscopic
spin Hamiltonian. We analyze
spin correlations within this
manifold and show that, for a fixed loop covering, they are determined by loop connectivity. We also project
symmetry-allowed perturbations into the ground-state
manifold and derive the resulting low-energy pseudospin dynamics. The checkerboard and pyrochlore cases differ sharply. On the pyrochlore
lattice, tetrahedral
symmetry removes simple local bias terms, and the leading nontrivial next-nearest-neighbour Heisenberg perturbation gives an emergent
spin-$\tfrac12$ XY model on the diamond
lattice of tetrahedron centers. These results give an exact
spin-$1$ microscopic starting point for constrained valence-bond physics in two and three dimensions, and show how loop, dimer, and gauge-theoretic descriptions can be approached from a small-
spin, SU(2)-invariant frustrated magnet.
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Statistical Mechanics · Cross-listed from nlin.AO
Swarming and Opinion Dynamics
Rommel Tchinda Djeudjo, Dibakar Ghosh and Timoteo Carletti
Collective dynamics in multi-
agent systems provide a powerful framework for understanding how coherent group-level patterns can emerge from simple interactions between individuals. Such phenomena are observed in many natural and artificial systems, including animal groups, robotic swarms, and distributed decision-making processes. In many situations,
agents are not only characterized by their spatial motion, but also by internal states, e.g., opinions or preferences, which evolve through interactions with peers. Understanding how these internal states influence collective motion, and how spatial organization in turn affects internal dynamics, remains an important challenge. In this work, we propose a model of coupled collective motion and opinion dynamics. The spatial dynamics are governed by attraction–repulsion interactions, while the internal dynamics are described by a Deffuant-type opinion model. Our results show that the confidence threshold of the opinion dynamics plays a key role in controlling the number of opinion clusters, whereas the strength of the opinion-dependent spatial attraction determines whether these clusters spatially merge or remain separated. In addition, for the full-consensus state, we derive the expression for the radius of the stationary swarm distribution when a nonlinear attraction kernel is used, using a semi-analytical approach. The proposed framework may be useful for studying collective decision-making, animal group behavior, and coordination strategies in swarm robotics.
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Mesoscale and Nanoscale Physics · Cross-listed from cs.ET
Reproducible Reservoir Computing with Thermally Driven Superparamagnets: Controlling Temperature Sensitivity
Zhengfei Chen, Alex Welbourne, Matthew O.A. Ellis et al. (+3 more)
Unconventional computing systems must demonstrate robust performance under real-world environmental conditions to enable practical deployments. We have recently proposed superparamagnetic nanodot ensembles driven by strain-induced magnetoelectric coupling as exciting candidates for use as ultra-low energy consumption reservoir computing substrates. However, because their dynamics are governed by thermal activation effects, these systems are intrinsically sensitive to ambient temperature fluctuations, leading to degraded task performance when operated outside the temperature range used during training. In this paper we simulate how temperature variations affect the magnetization dynamics of such superparamagnetic ensembles, and quantify how this affects task performance. We then show how heterogeneous nanodot patterns that incorporate different sizes of nanodots with different characteristic timescales for thermal activation mitigate this problem.
Benchmark results on the NARMA-10 task show that introducing optimized heterogeneity stabilizes performance of the reservoirs across a wide range of ambient temperatures (5-35{\deg}C), with little loss of ultimate performance. We also characterize the trade-off between performance and temperature stability and show that it can be tuned via reservoir hyperparameters. Our study demonstrates a key step in making these novel devices suitable for real-world deployment.
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All authors Zhengfei Chen, Alex Welbourne, Matthew O.A. Ellis, Dan A. Allwood, Eleni Vasilaki, Thomas J. Hayward
Strongly Correlated Electrons
Phase-shifted multicomponent spin-charge nematicity in an altermagnet
Christopher Candelora, Siyu Cheng, Muxian Xu et al. (+7 more)
Altermagnets host
spin-split
Fermi surfaces without net magnetization. This intrinsically multicomponent electronic setting raises the possibility that familiar correlated electron phases acquire unconventional
spin-charge structure. Here we report the discovery of altermagnetic nematicity in Co0.25NbSe2. Using spectroscopic-imaging scanning tunneling microscopy and
spin-polarized scanning tunneling microscopy, we find that the three nominally C3-related directions lose rotational equivalence in the zero-field state, in both charge and
spin-sensitive tunneling channels. Strikingly, the dominant
spin-sensitive component is shifted by one C3 sector relative to the dominant charge component, revealing a phase-shifted
spin-charge nematic response. A phenomenological theory shows that altermagnetic order favors a finite relative phase between the charge and
spin-sensitive nematic components – C3
lattice pinning frustrates this preferred offset and selects the observed phase locking. These results establish altermagnetic nematicity as a new form of multicomponent electronic
liquid-
crystal order and point to a potentially generic route by which altermagnets can transform conventional correlated phases into
symmetry-engineered
spin-charge orders.
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All authors Christopher Candelora, Siyu Cheng, Muxian Xu, Keyu Zeng, Hengxin Tan, Younghun Hwang, Binghai Yan, Federico Mazzola, Ziqiang Wang, Ilija Zeljkovic
Mesoscale and Nanoscale Physics
What Is the Real-Time Atomistic Mechanism Behind Chirality-Induced Spin Selectivity in Donor-Chiral Bridge-Acceptor Molecules?
Shu-Zheng Zhou, Xi Sun, Kai-Yuan Zhang et al. (+1 more)
Chiral-induced
spin selectivity (CISS) has been experimentally observed in photo-excited donor-
chiral bridge-acceptor (D-B{\chi}-A) molecules [Science 382, 197-201 (2023)]. However, the microscopic mechanism underlying CISS in such
chiral systems remains elusive. Here we develop a
quantum dynamical model that precisely maps the atomic structure of binaphthyl-type bridge dimers in isolated D-B{\chi}-A molecules and introduce a
geometric spin-orbit coupling (SOC) mechanism to unveil the intrinsic origin of CISS in axially
chiral systems. During photo-excited electron transport along the twisted pathways, the
geometric SOC coupling strength exceeds the intrinsic coupling of light atoms by one to two orders of magnitude, readily producing observable high
spin polarizations. The resulting
spin polarization comprises two components: the CISS-associated polarizations along and perpendicular to the
chiral axis are intrinsic to axial chirality, requiring neither external fields nor
spin-superexchange transfer, while a non-Abelian
curvature correction provides a rigorous mathematical definition of the
chiral axis direction. Our calculated polarization components, chirality dependence, and relative magnitudes (30-40%) quantitatively match time-resolved electron paramagnetic resonance measurements. This
geometric SOC framework offers a self-consistent and general physical picture of CISS in axially
chiral molecules and provides explicit theoretical guidance for the design of
chiral spintronic devices.
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All authors Shu-Zheng Zhou, Xi Sun, Kai-Yuan Zhang, Hua-Hua Fu
Statistical Mechanics · Cross-listed from astro-ph.HE
Supernova Neutrinos and the Origin of Biomolecular Homochirality
Amirmasoud Jannat, Soroush Shakeri and Farhad Shahbazi
We investigate the role of parity-violating interactions between
supernova neutrinos and
chiral molecules in nearby interstellar molecular clouds as a potential source of biomolecular homochirality. We introduce
neutrino interactions into the autocatalytic chemical reactions in a far-from-
equilibrium noise-induced system. These interactions create a directional bias between L and D enantiomers in the racemization reactions, which is amplified by autocatalysis and
stochastic fluctuations. We solve the
stochastic equations within the Ito sense to obtain the dynamics of the probability distribution of the enantiomeric excesses, offering an astrophysical scenario for the delivery of homochirality seeds to Earth by meteorites. In spite of the weak interactions of
supernova neutrinos, our framework introduces an amplification mechanism to yield a considerable enantiomeric excess of more than $10\%$, in agreement with the latest chemical analysis of the meteorites. Moreover, we scan over the parameter space of the model, inferring from the observational values in order to explore the window of opportunity to generate the initial seeds of homochiral states in interstellar molecular clouds.
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Materials Science · Cross-listed from physics.optics
Symmetry-Informed Deep Learning for Electromagnetic Scattering
Viktor A. Lilja and Philippe Tassin
Deep learning can accelerate the modeling of electromagnetic devices by replacing costly simulations with neural networks trained to map design parameters to scattering parameters. However, data efficiency remains a central bottleneck, as training data is typically generated through expensive numerical simulations. Here we show that
symmetry provides a powerful and largely untapped route to overcoming this limitation in electromagnetic scattering problems. Leveraging the equivariance of Maxwell's equations, we obtain general transformation rules that map
symmetries of electromagnetic devices to corresponding transformations of their scattering parameters. This enables both systematic data augmentation and the construction of exactly equivariant neural networks. We implement the framework for both discrete and continuous
symmetry groups and demonstrate its effectiveness on photonic-
crystal slabs and free-form diffraction gratings. Incorporating
symmetry improves data efficiency by an order of magnitude compared to standard architectures, while equivariant models additionally enforce physical constraints exactly. Our approach is general and complementary to existing physics-informed strategies, provides a first-principles framework for constructing physically grounded surrogate models, and establishes
symmetry as a unifying inductive bias for data-efficient and physically consistent learning in computational electromagnetics and beyond.
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Materials Science
Single-orbital tight-binding model for chiral one-dimensional hybrid organic-inorganic lead halide perovskites
Yuya Ominato, Tetsuya Furukawa, Ayumi Ishii et al. (+1 more)
We present a single-orbital tight-binding model for the low-energy electronic states of the
chiral one-dimensional hybrid organic-inorganic lead halide perovskite $\mathrm{(}R/S\mathrm{-PEA)PbI}_3$. The model is constructed from a single effective orbital on each of the four
symmetry-related sites in the primitive unit
cell and incorporates layer, in-plane sublattice, and
spin degrees of freedom. With separate parameter sets for the conduction and valence bands, the effective
Hamiltonian reproduces the overall band dispersions obtained from density-functional-theory calculations and quantitatively captures the
spin splittings near the band edges. It also captures the leading
spin-polarization patterns of the Bloch states, showing that the band-edge
spin splitting and
spin polarization are encoded in a small number of
symmetry-adapted
spin-dependent hopping terms. We further analyze the accidental degeneracies of the effective
Hamiltonian using screw
eigenvalues and antiunitary operators. This analysis separates accidental degeneracies originating from the restricted term content of the effective
Hamiltonian from degeneracies enforced by nonsymmorphic screw
symmetries and time-reversal
symmetry. The present model provides a
symmetry-transparent starting point for understanding the band-edge electronic structure of
chiral lead halide perovskites and for analyzing optical,
spin, and transport responses in this class of materials.
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All authors Yuya Ominato, Tetsuya Furukawa, Ayumi Ishii, Tetsuaki Itou
Materials Science
Strain-Tunable Shift Current and Magneto-Optical Kerr Effect in Multiferroic Altermagnet Fe2Mo3O8
Shengqiao Wang, Bo Zhao, Harish K. Singh et al. (+6 more)
Altermagnetism has recently emerged as a compelling frontier in spintronics, seamlessly merging the agile tunability of ferromagnets with the hallmark merits of antiferromagnets. As a prototypical polar multiferroic featuring distinctive altermagnetism, Fe2Mo3O8 hosts an ideal playground for exploring the intricate interplay among ferroelectric polarization, altermagnetic order, and
spin-dependent responses. Here, employing first-principles calculations, we systematically investigate the coupling among polarization,
spin splitting, shift current, and magneto-optical responses in Fe2Mo3O8. Our findings reveal that switching the ferroelectric polarization not only inverts the sign of the shift current but also comprehensively reshapes the momentum-space
spin-splitting texture. Furthermore, the shift current and magneto-optical spectrum exhibits strong tunability under mechanical strain. Remarkably, the application of a-axis uniaxial strain breaks the crystalline
symmetry, thereby activating a finite magneto-optical Kerr effect that is otherwise forbidden in the pristine phase.
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All authors Shengqiao Wang, Bo Zhao, Harish K. Singh, Jiahao Xie, Fu Li, Hongbin Zhang, Yang Su, Chen Shen, Lijun Zhang
Statistical Mechanics · Cross-listed from math.PR
Semi-open boundary for random walking shocks
Márton Balázs
Non-stationary time
evolution of interacting particle systems is in general a rather difficult topic however, exceptional examples are known where hidden processes within the model make the description manageable. These hidden processes often take the form of a finite number of interacting random walks and in some cases, rather than being hidden, were very explicitly revealed as second class particles associated with the model. The examples of asymmetric exclusion and exponential bricklayers model are known in this context, where such distributional structure was demonstrated in infinite volume. Here we find boundary mechanisms that save this remarkable structure in finite volume of the model with semi-open boundaries that let ordinary particles, but not the shocks, through. This finding also allows to characterise nontrivial two-species, non-reversible stationary distributions subject to our special boundary rates.
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Materials Science
Photogeneration and signatures of coherent phonons in time-resolved photoemission spectroscopy: First-principles time-dependent adiabatic GW approach
Yang-hao Chan, Zhenglu Li and Steven G. Louie
Coherent
lattice dynamics can be observed in pump-probe time-resolved and angle-resolved photoemission spectroscopy (TR-ARPES) as a periodic modulation of intensity and energy of photoelectrons over probe time. We present an ab initio time-dependent GW approach including electron-
phonon (e-ph) couplings to simulate the photogeneration of coherent
phonons and their effects on the TR-ARPES of monolayer MoS2. We demonstrate that state-resolved e-ph coupling strength can be obtained from analyzing coherent
phonon modulations on TR-ARPES. Features of both the impulsive stimulated Raman scattering mechanism and the displacive excitation mechanism of coherent
phonon generation are identified in our simulations. We clarify their origins and the coincident selection rule of coherent
phonon generation and Raman scattering intensity. This method provides supports to analyze coherent
phonon dynamics and e-ph couplings in TR-ARPES and enables quantitative engineering of band structure through coherent
phonons.
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Materials Science
The self-organized vacancy order in Pr$_9$Ge$_{16}$
Jayashani S. T. Wickramasinghe, Melissa G. Anderson, Kelci Graville et al. (+11 more)
In this work, we report the discovery of a new
crystal structure on the Ge-rich side of the Pr-Ge binary phase diagram. Using a high-temperature flux technique, we grew single
crystals of $Pr_9Ge_{16}$, which adopt a previously unreported orthorhombic $Fdd$2 structure type featuring ordered Ge vacancies. We present the anisotropic
magnetic properties and identify the crystallographic $b$ axis perpendicular to the
crystal plane as the
magnetic easy axis. Temperature-dependent resistivity measurements reveal metallic behavior with a distinct anomaly at $T_{\mathrm{C}}$ = 14.3 K.
Hall resistivity data indicate that electron-like carriers dominate, with a carrier concentration on the order of $10^{27}~\mathrm{m}^{-3}$. The
magnetic order is readily suppressed by a
magnetic field of approximately 0.4 T applied along the easy $b$ axis.
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All authors Jayashani S. T. Wickramasinghe, Melissa G. Anderson, Kelci Graville, Gregory T. McCandless, Zachary J. Morgan, Brianna R. Billingsley, Tai Kong, Hyunsoo Kim, Aleksandr V. Chernatynskiy, Simon G. Mitchell, Liang Wu, Julia Y. Chan, Feng Ye, Halyna Hodovanets
Strongly Correlated Electrons
Emergent $s+id$ Superconductivity from the Interplay between Electronic Correlations and Electron-Phonon Coupling in $\mathrm{R}_{1-x}\mathrm{Sr}_x\mathrm{NiO}_2$
Zi Yuan, Jun Zhan, Xianxin Wu et al. (+1 more)
Recent tunneling measurements on infinite-layer nickelates have revealed spatially varying superconducting
symmetries, whose microscopic origin remains unclear. Motivated by this observation, we investigate the interplay between electron correlations and electron-
phonon interactions in infinite-layer nickelates by combining first-principles calculations with the fluctuation-exchange-Migdal-Eliashberg theory. Our calculations show that
spin fluctuations yield robust $d$-wave superconductivity on the Ni $d_{x^2-y^2}$ orbital, whereas electron-
phonon coupling induces $s$-wave pairing on an interstitial orbital, leading to an $s+id$ superconducting state. The emergence of the $s$-wave component is strongly carrier-density dependent: an intermediate electron-
phonon coupling of $\lambda=0.4$ stabilizes the $s+id$ state at $n=0.9$ but not at $n=0.8$. These results imply that local oxygen defects tune the local electron density and form finite-size domains with distinct pairing
symmetries, offering a compelling explanation for the spatially inhomogeneous superconducting
symmetries observed in experiments.
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All authors Zi Yuan, Jun Zhan, Xianxin Wu, Shaozhi Li
Soft Condensed Matter
Entropy-Driven Initiation and Cellular Uptake Mediated by Viscoelastic Cytoskeleton: A Kinetic Phase Diagram from Onsager Variational Principle
Jinjie Liu, Zhong-Can Ou-Yang and Hao Wu
A fundamental question in receptor-mediated endocytosis remains unanswered: what initial driving force brings ligands and receptors into close proximity? While previous models assume pre-existing contact and overlook this initiation problem, we propose that entropic forces from nanoscale biomolecules in crowded cellular environments provide the essential driving mechanism. We develop a unified continuum model rooted in the Onsager variational principle, where engulfment depth serves as the generalized coordinate and the driving force derives from a free energy landscape of entropic, binding, membrane, and cytoskeleton contributions. The framework naturally incorporates: (i)
entropy-driven adhesion as initiation; (ii) ligand-receptor binding as the sustaining force; (iii) membrane deformation via the Helfrich-Canham
Hamiltonian; and (iv) cytoskeleton viscoelasticity through the elastic-viscoelastic correspondence principle. The kinetic phase diagram predicts a critical biomolecule concentration for initiation, a lower bound of ligand density for complete engulfment, a finite size window for engulfable particles, and an optimal virus radius of 30–60 nm that decreases with increasing binding energy. The Onsager solubility condition naturally yields the phase boundaries. The model exhibits asymptotic consistency with the classic Asakura-Oosawa result in the large-particle flat-surface limit. Stiffer
cells lead to longer engulfment times and narrower size windows. Strikingly, the optimal size matches HIV-1 dimensions under physiologically realistic parameters. This work provides a variational foundation for cellular uptake with implications for virology, nanotechnology, and drug delivery.
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Mesoscale and Nanoscale Physics
Dynamical Generation of Rectified Electric Current
Jin-Xin Hu and Congjun Wu
Rectification is a fundamental nonlinear transport process that converts an alternating drive into a direct current. In this work, we propose a general theoretical framework for electric current rectification triggered by a dynamical external drive that couples to an arbitrary well-defined operator of a periodic system, and which in the static limit forbids any steady current. In the dynamical regime, the finite frequency $\Omega$ of the time-varying drive breaks time-translation invariance and injects energy into the system, enabling a second-order nonlinear rectified current that has no static counterpart. This rectification process has two distinct origins: (i) an
impurity-scattering-modified distribution function at finite frequency, and (ii) a time-domain anomalous velocity stemming from a dynamical mixed Berry
curvature. Both contributions persist when the driving frequency lies well below the optical transition gap. Applying our general theory to a buckled
magnetic system subject to an out-of-plane oscillating electric field, we characterize the generated current as a nonlinear magnetoelectric gyrotropic effect and predict that the induced rectified current is sensitive to the
magnetic order, thereby offering a feasible electrical probe of Néel order in non-coplanar antiferromagnets.
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Materials Science
Antiphase boundary-driven large exchange bias and negative magnetoresistance in NiCo2O4
Biswanath Pramanik, Pushpesh Pathak and Binoy K. Hazra
Nickel-based spinel
oxide has recently attracted significant
attention due to its remarkable magneto-transport properties, promising various spintronic applications. In this study, we observe an exchange bias effect, where the
magnetic hysteresis loop shifts both horizontally and vertically when single-phase nanocrystalline NiCo2O4 is cooled in the presence of an external
magnetic field. The magnitude of the exchange bias field is approximately 375 Oe at 5 K, and this effect disappears around 300 K. Furthermore, NiCo2O4 shows semiconducting behaviour in longitudinal resistivity and demonstrates a substantial negative magnetoresistance of ~31.5% at 10 K. The magnetoresistance exhibits a butterfly-shaped behaviour at low
magnetic fields and becomes almost linear at high
magnetic fields. A detailed analysis of the negative magnetoresistance and exchange bias reveals that both phenomena originate from the formation of antiphase boundaries in the as-synthesized NiCo2O4 sample, as confirmed by the high-resolution transmission electron micrograph.
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Strongly Correlated Electrons
Magnetic field-driven phase switching in the antiferromagnetic Mott insulator Ca$_3$(Ru$_{0.99}$Ti$_{0.01}$)$_2$O$_7$
Ksenia S. Rabinovich, Tim Priessnitz, Nils Gross et al. (+7 more)
A bandwidth-controlled
antiferromagnetic Mott-insulating phase in Ca$_3$(Ru$_{1-x}$Ti$_x$)$_2$O$_7$ is realized through isovalent substitution at the Ru site. For a dilute substitution with only 1% Ti, the Mott
insulator ground state remains nearly degenerate with the ground state of pristine Ca$_3$Ru$_2$O$_7$, where the Ru moments are ferromagnetically aligned within the metallic RuO$_2$
bilayers stacked in an
antiferromagnetic fashion. The exceptionally shallow free energy landscape of this doped compound arises from intertwined electron-electron and electron-
lattice interactions. This makes its
magnetic and transport properties highly sensitive to external perturbations. We systematically investigated
magnetic-field-induced phase switching in Ca$_3$(Ru$_{0.99}$Ti$_{0.01}$)$_2$O$_7$ to explore its
magnetic $H$-$T$ phase diagram. With the field applied along the easy $b$-axis, parallel to the
antiferromagnetic moments, the magnetization exhibits a first-order
spin-flop transition at $\approx $ 6 T, indicating reorientation of the Ru moments perpendicular to the field. The transition is accompanied by a decrease in the electrical resistance, but the
spin-flop phase remains insulating. Above 10.5 T, all Ru moments align with the $b$-axis, resulting in a forced
ferromagnetic metallic phase. In contrast, neither
spin-flop nor forced-
ferromagnetic phases are observed up to 14 T, when the field is applied along the $a$-axis. While the electronic kinetic energy and the electron-
lattice coupling contribute to the free-energy balance of this system, the resulting $H$-$T$ phase diagram is remarkably simple and closely resembles that of a canonical anisotropic antiferromagnet, albeit with substantially renormalized critical fields.
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All authors Ksenia S. Rabinovich, Tim Priessnitz, Nils Gross, George Jackeli, Maximilian J. Krautloher, Pascal Reiss, Eberhard J. Goering, Jurgen H. Smet, Bernhard Keimer, Alexander V. Boris
Statistical Mechanics
Emergence of drifted diffusion in quantum walks with subspace restart
Liwei Qiao, Ruoyu Yin and Wei Zhang
Restart of a
quantum process is typically modeled as a global reinitialization that erases the system's entire history. Here we introduce subspace restart, a protocol that periodically resets only the internal degrees of freedom while preserving the spatial distribution, as a tunable knob for the
quantum-to-classical crossover. Using the discrete-time
quantum walk as an example, we show that this selective reset drives the walker into an engineered drifted-
diffusion regime. This phenomenon can be understood by a Huygens-Fresnel mechanism, where each restart fragments the wave function into a set of independent secondary sources to screen long-range correlations and isolate a robust classical backbone, whose drift and diffusivity are set by the
geometric orientation of the initial coin and the restart period. Residual
quantum interference, confined to effective light cones, survives only as a short-range correction that renormalizes these coefficients and imprints periodic modulations on the cumulants. Our results establish subspace restart as a route to controlling the
quantum-to-classical crossover in synthetic
lattices.
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Mesoscale and Nanoscale Physics
Geometric Spin-Orbit Coupling Resolves the Contradictory CISS Effect in Chiral Single Molecules
Shu-Zheng Zhou, Xi Sun, Kai-Yuan Zhang et al. (+1 more)
Some studies have reported clear chirality-induced
spin selectivity (CISS) effect in four classes of
chiral single molecules with remarkable
spin polarization. In contrast, a recent high-precision measurement involving nearly a thousand individual tests failed to detect significant CISS signals in the same molecular systems (J. Am. Chem. Soc. 2025, 147, 25043). These conflicting results cast doubt on whether CISS truly occurs in these
chiral systems at the single-molecular level. To resolve this discrepancy, we develop a theoretical framework incorporating
geometric spin-orbit coupling and environmental decoherence, enabling systematic study of the CISS in four
chiral single molecules with distinct geometries and sizes. Our calculations show that the CISS effect is completely suppressed in both strong-coherence and strong-decoherence regimes, but becomes pronounced in the intermediate-decoherence regime, where observable
spin polarization emerges. In the strong-coherence regime, both electron-electron interaction and electron-vibration coupling enhance the CISS effect: the former is more effective in large molecules, whereas the latter plays a more significant role in smaller ones. Increasing temperature further enhances
spin polarization. The proposed mechanism unifies contradictory experimental observations and reveals how the CISS effect evolves from regular helical (helical symmetric) to irregular helical (point-symmetric or axially symmetric) chirality. This framework thus provides a basis for unifying CISS phenomena across single-molecule systems, regardless of their specific molecular configurations or
symmetry classes.
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All authors Shu-Zheng Zhou, Xi Sun, Kai-Yuan Zhang, Hua-Hua Fu
Materials Science · Cross-listed from physics.ins-det
Influence of compaction pressure on the impedance of Gadolinium Doped Ceria electrolytes for IT-SOFCs
Renato A. N. de Oliveira, Celeste Z.A. Aquino, Magna Monteiro Schaerer et al. (+15 more)
Gadolinium doped ceria (GDC) is one promising oxygen-ion conducting ceramic electrolyte for intermediate-temperature solid
oxide fuel
cells (IT-SOFCs), due to its high ionic conductivity at reduced operating temperatures, favorable defect chemistry, and compatibility with a broad range of electrode materials [1,2]. Despite extensive understanding of its intrinsic ion transport mechanisms, the influence of ceramic processing parameters on the effective electrical behavior of polycrystalline GDC electrolytes remains an active topic for investigation [3-5]. In particular, processing steps that govern green body formation and sintering can strongly affect microstructural features such as density, grain size, grain boundary character, and residual porosity, which in turn determine the macroscopic conductivity [4-6]. In this work, dense GDC ceramic pellets were fabricated under systematically varied isostatic compaction pressures ranging from 49 to 140 MPa, followed by sintering at 1350 C for four hours under identical thermal conditions. Platinum electrodes were deposited on both sides of the pellets by electron-beam deposition, and the electrical properties were characterized by electrochemical impedance spectroscopy (EIS) over a wide temperature range. The results demonstrate a dependence of the impedance with respect to compaction pressure.
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All authors Renato A. N. de Oliveira, Celeste Z.A. Aquino, Magna Monteiro Schaerer, Rafael Galiza Yoshimura, Liliana Mogni, Maurico Arce, Diego G. Lamas, Lucia Toscani, Maria Belén Arcentales Vera, Esteban Elvis Asto Ramos, Marcia Carvalho de Abreu Fantini, Taofeeq Oladayo Bello, Tereza da Silva Martins, Danilo Waismann Losito, James Moraes de Almeida, Valeria Spolon Marangoni, Leopoldo Suescunand, Santiago Figueroa
Quantum Gases
Standard basis operator method for ground-state and temperature properties of single and two-component Bose-Hubbard model
Oliwier Urbański and Tomasz P. Polak
We formulate an improved standard basis operator (SBO) method for the single and two-component Bose-Hubbard model in three dimensions. In the first case, nonzero temperature predictions are qualitatively and quantitatively enhanced by taking into account necessary number of on-site states, not just three as in previous works. Performance of the final numerical calculations is also improved by asymptotic analysis of the self-consistent equations near the critical line. Obtained results are compared with Monte-Carlo, tensor networks,
Quantum Rotor Approach and experimental data. In the two-component case, SBO generalizes rather poorly, being able to account for intra-species thermal and
quantum fluctuations, but not the inter-species ones. Deeper reasons for this situation are discussed. Still however, non-trivial deformation of the phase diagrams is predicted, together with first-order phase transitions steered by the changes in chemical potential.
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Statistical Mechanics · Cross-listed from quant-ph
Thermal Activation of Divergent Distillable Entanglement under Non-Abelian Strong Symmetry
Shuai Zeng
Heating usually destroys
quantum entanglement. We show that thermalization constrained to a non-Abelian strong-
symmetry sector can instead generate a distillable resource that diverges with system size. In an exactly solvable local dimer chain,
entanglement across an equal bipartition is exactly zero at $T=0$, whereas every fixed $T>0$ yields $E_D=\frac12\log_2 N+C(T)+o(1)$. Measurements of the two half-chain representation labels convert thermally populated non-Abelian sectors into standard ebits. More generally, for global-singlet thermal states of finite-range, uniformly bounded, locally $SU(2)$-invariant chains, there is a nonzero high-temperature interval in which the protocol yield satisfies $Y_N=\frac12\log_2 N+O_\beta(1)$ and $E_D\geq Y_N$. For the dimer chain, the full finite-size onset is governed by a universal Bessel-function crossover with $T_*(N)=\Delta/[\ln N+O(1)]$. Exact diagonalization of a frustrated $J_1$-$J_2$ chain shows the expected finite-size signatures. Thus thermal fluctuations can create
entanglement across a macroscopic cut and convert it into an unbounded operational
quantum resource.
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Soft Condensed Matter
How Quasicrystals Remember: Hierarchical Memory Under Cyclic Shear
Edwin A. Bedolla-Montiel and Marjolein Dijkstra
Quasicrystals occupy a unique middle ground between periodically ordered
crystals and disordered glasses, making them an ideal platform for examining the interplay between disorder and the emergence of mechanical
memory. Using athermal quasistatic shear simulations, we show that two-dimensional dodecagonal quasicrystals encode and recover
memory under cyclic driving. Above the yielding transition, the response becomes irreversible, characterized by persistent shear bands and locally transformed regions. Below yielding, cyclic shear with varying amplitudes produces a hierarchy of nested hysteresis loops in the stress-strain response characteristic of loop-return point
memory. By resolving the underlying reversible plastic events, we reveal localized phason-like tile rearrangements as the elementary switching units and identify tile-switch hysterons responsible for
memory in the quasicrystal. Such a microscopic identification of the fundamental switching units is considerably more challenging, and often impossible, in amorphous solids. Despite their structural diversity, these rearrangements share a compact core, sharp bistability, and an Eshelby-compatible elastic far field. In contrast, a periodic approximant of the quasicrystal lacks both the structural disorder and the bistable tile-switch rearrangements required for cyclic-shear
memory, linking phason degrees of freedom to bistable hysterons.
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Materials Science
Emergent exchange bias in ultra-thin La0.67Sr0.33MnO3 films driven by ferro-antiferromagnetic phase coexistence
Inés García-Manuz, Gabriel Caballero, Jose Luis F. Cunado et al. (+7 more)
Ultra-thin La0.67Sr0.33MnO3 (LSMO) films are generally regarded as single-phase ferromagnets, yet their reduced dimensionality enhances the impact of oxygen stoichiometry and local structural distortions. Here we demonstrate that LSMO layers with thicknesses between 3 and 17 nm develop a robust and thickness-independent exchange bias (EB) despite the absence of an engineered
ferromagnetic-
antiferromagnetic (FM-AFM) interface. Angular magneto-optical Kerr effect measurements reveal a reproducible hysteresis-loop shift that reverses sign upon 180-degree rotation, confirming its intrinsic origin. X-ray photoelectron spectroscopy shows a thickness-independent Mn2+ fraction (about 20 percent), indicating the presence of oxygen-deficient reduced regions embedded within the Mn3+/Mn4+
ferromagnetic matrix. A simple interfacial-exchange model suggests that only a sub-percent fraction of
antiferromagnetic (or frustrated
spin-ice-like) regions is required to generate the observed EB. These results demonstrate that ultra-thin LSMO can spontaneously host internal FM-AFM interfaces driven by oxygen deficiency, revealing an emergent route to exchange bias in nominally single-phase manganite films.
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All authors Inés García-Manuz, Gabriel Caballero, Jose Luis F. Cunado, Miguel Romera, Mariela Menghini, Carlos León, Jacobo Santamaría, Julio Camarero, Paolo Perna, Fernando Ajejas
Materials Science · Cross-listed from physics.ins-det
A critical consideration of X-ray detectors based on Ga2O3: excitation, carrier transport mechanisms and performance standardization
Alfred Moore, Daniel A Lamb, Lijie Li et al. (+11 more)
X-ray detection underpins a wide range of applications in medicine, security, industrial inspection, scientific research for non-destructive imaging and material analysis. The rapid development of Ga2O3-based X-ray detectors offers a promising pathway toward next-generation detectors with high sensitivity, low noise, and harsh environment applications, benefiting from its intrinsic material properties such as high density, wide band gap energy, and high thermal-chemical stability. However, the underlying device operating mechanisms, including both carrier excitation and transport processes, have not yet been adequately studied, largely due to the misuse of X-ray sources in previous studies. Besides, benchmarking of device characteristics has been problematic due to experimental or data analysis issues, as well as misunderstandings of the applied equations associated with parameter definitions. In this work, we have designed and performed an instructive research work based on epitaxial beta-Ga2O3:Si and its planar Schottky detectors, measured with energy-tuneable monochromatic X-ray beams on a synchrotron beamline, clarifying the device excitation and carrier transport mechanisms with properly benchmarked device performance. In the end, we propose a set of protocols for correctly measuring and analysing the device performance. The proposed protocols are broadly applicable and can be readily extended to other
semiconductor X-ray detectors.
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All authors Alfred Moore, Daniel A Lamb, Lijie Li, Oliver Fox, Kawal Sawhney, Ciaran Llewelyn, Jon E Evans, Saqib Rafique, Tiantian Chai, John Harrington, Zabeada Aslam, Andrew P Brown, Rik Drummond-Brydson, Yaonan Hou
Strongly Correlated Electrons
Halogen control of magnetic competition in Kitaev candidate Ru$X_3$ ($X =$ Cl, Br)
Ryuta Iwazaki, Shinnosuke Koyama, Takashi Koretsune et al. (+2 more)
The
spin-orbital Mott
insulators Ru$X_3$ ($X =$ Cl, Br) have attracted considerable
attention as promising candidate materials for realizing a Kitaev
spin liquid. In this study, we construct effective pseudospin models from multiorbital Hubbard models derived from first-principles calculations and investigate the
magnetic states of RuCl$_3$ and RuBr$_3$. From the constructed effective models, we find that RuBr$_3$ has more extended Wannier orbitals and stronger interlayer exchange interactions than RuCl$_3$. These interactions enhance three-dimensional correlations, consistent with the stronger
antiferromagnetic tendency experimentally inferred for RuBr$_3$. Orbital-dependent Coulomb anisotropy further reduces the energy difference between
ferromagnetic and zigzag states. Our results clarify how halogen substitution controls
magnetic competition in Ru$X_3$ through interlayer exchange interactions and effects of orbital-dependent Coulomb interactions.
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All authors Ryuta Iwazaki, Shinnosuke Koyama, Takashi Koretsune, Shintaro Hoshino, Joji Nasu
Strongly Correlated Electrons · Cross-listed from hep-lat
Lattice Configuration Generation with a Self-Learning Diffusion Model
Akio Tomiya
We show that a
diffusion sampler for
lattice-field configurations can be self-trained without preparing target-ensemble training configurations using an external Monte Carlo calculation. Starting from exactly sampled configurations at $\beta=0$, we use action-difference weights to train the score at the next coupling. Proposals from a fixed model are Metropolis-Hastings corrected at every noise level, and the resulting chain supplies training configurations for the next stage. This procedure defines the self-learning
diffusion sampler SLDiffusion. In the two-dimensional compact XY model, self-training proceeds from $\beta=0.30$ to $0.50$ at $L=4$ and extends to $L=6,8,12$ at $\beta=0.5$. The energy and
vortex densities agree with independent Hybrid Monte Carlo calculations within $1.6$ combined standard errors. Their integrated autocorrelation times, measured in stored updates, remain below two at all volumes studied. These results demonstrate a
diffusion sampler whose training can be initialized and continued without external target-coupling ensembles.
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