Materials Science
Spin-polarized Energy Density Method from Spin-Density Functional Theory
Yang Dan and Dallas R. Trinkle
The energy density method is generalized to include
spin polarization with the full formalism derived based on
spin-density functional theory, which aims at decomposing the total energy into well-defined atomic energies. The method involves two steps: (1) decomposing the total energy into
spin-polarized energy density functions in real space, and (2) integrating these energy densities over chosen gauge-invariant volumes for uniquely defined atomic energies, whose summation over all the atoms restores the DFT total energy up to a constant difference. This method is numerically implemented into the Vienna ab initio simulation package for the projector augmented-wave method, and is showcased with two applications. In the first application, we model the paramagnetic face-centered cubic Fe using
spin special quasirandom structures; the
spin energies are fit to
spin cluster expansions and a deep neural network. In the second application, we calculate the atomic energy distributions of dilute
magnetic semiconductor Ni-doped GaN with different dopant distances and
spin configurations. This method extracts additional useful information for the study of
magnetic systems with density functional theory.
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Materials Science
Carrier scattering considerations and thermoelectric power factors of half-Heuslers
Rajeev Dutt, Bhawna Sahni, Yao Zhao et al. (+7 more)
The electronic and thermoelectric (TE) transport properties of 13 n-type and p-type half-Heusler
alloys are computationally examined using Boltzmann transport. The electronic scattering times resulting from all relevant
phonon interactions and ionized
impurity scattering (IIS) are fully accounted for using ab initio extracted parameters. We find that at room temperature the average peak TE power factors (PF) of all materials we examine reside between 5 and 10 mW/mK$^2$. We also find that IIS in combination with the long range polar optical
phonon (POP) scattering are more influential in determining the electronic transport and PF over all other non-polar
phonon interactions (acoustic and optical
phonon transport). In fact, the combination of POP and IIS determines the thermoelectric power factor of the half-Heuslers examined on average by about 65%. The results highlight the crucial impact of Coulombic scattering process (POP and IIS) on the TE properties of half-Heusler
alloys and provide profound insight for understanding transport, which can be applied widely in other complex bandstructure materials. In terms of computation expense, the computationally cheaper POP and IIS provide an acceptable first-order estimate of the power factor of these materials, while the non-polar contributions, which require more expensive ab initio calculations, could be of secondary importance.
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All authors Rajeev Dutt, Bhawna Sahni, Yao Zhao, Yuji Go, Saff E Awal Akhtar, Ankit Kumar, Sumit Kukreti, Patrizio Graziosi, Zhen Li, Neophytos Neophytou
Strongly Correlated Electrons
Apparent Planckian scattering from local polaron formation
Brian Yong-Ho Lee and Chaitanya Murthy
We propose a simple mechanism for apparent Planckian scattering based on local polaron formation, in which $\Gamma_\text{tr} = \Gamma_0 + \alpha k_BT / \hbar$ with $\alpha \sim O(1)$ emerges from quasielastic scattering without fine tuning. We provide evidence for our proposal in Monte Carlo simulations of the Holstein model with disordered electron-
phonon coupling in the adiabatic limit. Our mechanism generates a finite interval of couplings in which the slope $\alpha$ is approximately constant, coinciding with the onset of local polaron formation. In this regime, Matthiessen's rule is dramatically violated (or obeyed, depending on one's point of view) in that changes to the couplings, which in perturbation theory would alter the slope $\alpha$, instead change the intercept $\Gamma_0$. We
conjecture that a version of our mechanism applies to any system with a dominant disordered interaction that can drive polaron formation. This potentially includes regimes of several recently introduced strange metal models based on spatially random interactions.
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Statistical Mechanics · Cross-listed from quant-ph
Entanglement and information scrambling in long-range measurement-only circuits
Abigail McClain Gomez, Fiona Abney-McPeek, Hong-Ye Hu et al. (+2 more)
Measurement-only
circuits provide a minimal setting in which repeated local projections can either generate or suppress many-body
entanglement, giving rise to measurement-induced phase transitions and dynamical regimes, that might have no
unitary counterpart. Here we investigate
entanglement and information transitions in one-dimensional measurement-only Clifford
circuits with long-range two-
qubit parity checks. By tuning both the measurement range and density per layer, we uncover a broad set of phases whose classification requires probes beyond
entanglement entropy, such as mutual information, tripartite mutual information, purification from an ancilla, and Bell-cluster statistics. We map phase diagrams using large-scale Clifford simulations for two protocols: a random-basis design in which each measurement is randomly chosen from $\lbrace XX,YY,ZZ \rbrace$, and a single-basis design in which the basis is fixed within each layer but varies between layers, hence introducing more structure to the
circuit. We map the trajectory-averaged
entanglement entropy to a two-dimensional statistical mechanics model by extending a replica-based method to random-basis measurement-only
circuits, and show that a continuous-time limit yields an effective long-range XX
hamiltonian in the steady state. This connection links the observed volume-law to sub-volume-law
entanglement transition to the boundary between a continuous
symmetry broken phase and a critical XY phase. Strikingly, in structured (single-basis)
circuits we find a phase in which volume-law and long-range
entanglement coexists with rapid, size-independent purification of an ancilla
qubit, and the absence of scrambling, highlighting measurement-only
circuits as a promising route to efficiently preparing highly entangled and technologically useful
quantum states.
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All authors Abigail McClain Gomez, Fiona Abney-McPeek, Hong-Ye Hu, Susanne F. Yelin, Ceren B. Dağ
Materials Science
How Electrons Become Mobile in a Colossal Dielectric – Fe$_2$TiO$_5$
M. L. McLanahan and A. P. Ramirez
We measure the colossal permittivity in single
crystal Fe$_2$TiO$_5$ using broadband spectroscopy in the frequency range 20 Hz - 1 MHz. The relaxation response is analyzed using a Debye-like model with Arrhenius activation in two different ways and yields an energy barrier of 286.1 $\pm$ 2.8 meV. DC transport yields an activation energy of 288.8 $\pm$ 2.8 meV. These results strongly imply that the energy barrier for localized dipole motion and itinerant charge transport originate from the same atom-level forces. A further implication is that colossal dielectric behavior is a microscopic bulk phenomenon arising from a system on brink of
metallicity.
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Disordered Systems and Neural Networks
Floquet mobility edges and transport in a periodically driven generalized Aubry-André model
Jayashis Das, Vatsana Tiwari, Manish Kumar et al. (+1 more)
We investigate the effect of a periodic electric field drive on the generalized Aubry-André model, also known as the Ganeshan-Pixley-Das Sarma (GPD) model, which is well known as a host of mobility edges. Our study of the Floquet spectrum of the driven GPD model uncovers the emergence of two distinct Floquet mobility edges, a delocalized–localized (DL) edge in the bounded regime, and a multifractal–localized (ML) edge in the unbounded regime. Using analytical results derived from Avila's global theory applied to the high frequency effective
Hamiltonian, together with numerical diagnostics such as the fractal dimension and inverse participation ratio, we demonstrate that these mobility edges can be effectively controlled by the amplitude and frequency of the electric field drive. We also identify drive-induced localization at specific values of the driving parameters, corresponding to dynamical localization points in the absence of quasiperiodic potential. Furthermore, the dynamical study of the periodically driven GPD model demonstrates superdiffusive to almost ballistic transport in the bounded regime corresponding to the DL edges, whereas subdiffusive transport is observed in the unbounded regime associated with the ML edges. We also analyze deviations from the high-frequency effective description by explicitly examining the low-frequency driving regime, where significant and counterintuitive deviations in both spectral properties and transport behavior are observed. Our study highlights the interplay of a quasiperiodic potential and a periodically varying electric field drive as a powerful mechanism to engineer mobility edges and control transport in systems with rich spectral features.
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All authors Jayashis Das, Vatsana Tiwari, Manish Kumar, Auditya Sharma
Strongly Correlated Electrons
Anisotropy of spin waves in the field-polarized phase of Fe-doped MnSi
I. N. Khoroshiy, A. Podlesnyak, D. Menzel et al. (+4 more)
Chiral magnetic textures, such as skyrmions, are of great interest to the condensed matter community due to their novel transport properties. The stabilization of topologically non-trivial
magnetic phases, like the skyrmion
lattice in cubic MnSi, is governed by underlying
magnetic interactions which can be probed via measurements of
spin-wave excitations. Here, we report high-resolution inelastic
neutron scattering (INS) measurements of the
spin waves in Fe-doped Mn$_{0.9}$Fe$_{0.1}$Si deep within its field-polarized
ferromagnetic state. We observe non-reciprocal
spin waves with a
parabolic dispersion that shifts linearly with
magnetic field. Crucially, the
spin-wave stiffness is highly anisotropic, with values of 17.2(5) meV~$\rm{\mathring{A}}$$^2$ parallel to the applied field and 9.3(3) meV~$\rm{\mathring{A}}$$^2$ perpendicular to it. While the applied field fundamentally lowers the systems
symmetry from cubic to uniaxial, we demonstrate that the induced
spin-wave anisotropy is significantly large, which is not captured within the simple theoretical approximations widely applied up to date.
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All authors I. N. Khoroshiy, A. Podlesnyak, D. Menzel, M. C. Rahn, D. S. Inosov, A. S. Sukhanov, S. E. Nikitin
Strongly Correlated Electrons
Beyond Variational Bias: Resolving Intertwined Orders in the Hubbard Model
Luciano Loris Viteritti, Riccardo Rende, Christopher Roth et al. (+3 more)
The two-dimensional Hubbard model at finite doping hosts competing or intertwined orders, resulting in conflicting conclusions from different computational approaches regarding its ground state. We show that a key source of such discrepancies is the bias encoded in the variational ansatz. We consider three different
Transformer backflow fermionic wave functions based on a Slater determinant, its particle-hole counterpart, and a Pfaffian, initialized without any mean-field pretraining. We show that, despite achieving nearly degenerate, state-of-the-art variational energies, each ansatz converges to a state with qualitatively different
spin, charge, and pairing correlations. Upon improving accuracy via
symmetry restoration and variance reduction, however, all three converge to the same physical picture: coexisting superconducting and stripe orders. These results demonstrate that variational energy alone is insufficient to identify the ground state in the presence of competing phases, and highlight the importance of tracking how correlation functions evolve as the wave function is systematically improved before drawing physical conclusions.
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All authors Luciano Loris Viteritti, Riccardo Rende, Christopher Roth, Anirvan Sengupta, Giuseppe Carleo, Antoine Georges
Strongly Correlated Electrons
Field-driven phases in a three-dimensional twisted Kitaev model for CoNb$_2$O$_6$: Interplay of frustration and spin-orbit coupling
Tom Drechsler and Matthias Vojta
The Ising chain in a transverse field stands out as a paradigmatic example for a
quantum phase transition. CoNb$_2$O$_6$ has been discussed as a material realization of this physics, but it was later realized that its
magnetic exchange couplings are more complicated, taking the form of twisted Kitaev chains. Here we study a three-dimensional model for CoNb$_2$O$_6$, taking into account both Kitaev physics and frustrated interchain coupling, in applied
magnetic field. Using semiclassical techniques at zero temperature, we map out the sequence of field-driven phases for arbitrary field direction; these include phases with commensurate and incommensurate interchain order. As a result of
spin-orbit coupling, the phase diagram is extremely sensitive to small changes in the field angle. We compute static observables as well as
magnetic excitation spectra in the various phases and connect our results to existing experimental data.
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Mesoscale and Nanoscale Physics · Cross-listed from hep-ph
Dive deeper with SUBMARINE: SUB-Mev dArk matter diRect detectIon using bilayer grapheNE
Rinchen Sherpa, Anuvab Sarkar, Tarak Nath Maity et al. (+3 more)
Novel target materials with anisotropic response will play a key role in detecting low-mass dark matter in upcoming experiments.
Bilayer graphene is one such material that has been proposed for the detection of sub-MeV mass dark matter particles via electronic excitations. In this work, we calculate scattering rate via a massive mediator in
bilayer graphene. With an exposure as small as $\sim$ 0.5 mg-year,
bilayer graphene can probe new regions of the parameter space. The anisotropic response function of
bilayer graphene leads to a sidereal-day modulation in the scattering rate, depending on its orientation with respect to the
Galactic dark matter wind. We find significant modulation in the scattering rate for sub-MeV mass dark matter, demonstrating
bilayer graphene's promise for a future experiment. We hope that our work will motivate the community to investigate
bilayer graphene as a novel target material, and that it may lead us to discover the particle nature of dark matter.
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All authors Rinchen Sherpa, Anuvab Sarkar, Tarak Nath Maity, Paramita Dutta, Ranjan Laha, Anirban Das
Statistical Mechanics · Cross-listed from quant-ph
Algorithmic Locality of Quantum Tensor Network Belief Propagation
Siddhant Midha, Yifan F. Zhang, Daniel Malz et al. (+2 more)
Belief propagation has recently emerged as a powerful framework for evaluating tensor networks in higher dimensions, combining computational efficiency with provable analytical guarantees. In this work, we develop the first end-to-end theory of tensor network belief propagation for a class of projected entangled pair states satisfying strong injectivity. We show that when the injectivity parameter exceeds a constant threshold, BP fixed points can be found efficiently, and a cluster-corrected BP
algorithm computes physical quantities to $1/\mathrm{poly}(N)$ error in $\mathrm{poly}(N)$ time for an $N$
qubit system. We further identify a striking phenomenon we term algorithmic locality: local perturbations of the tensor network affect the BP fixed point with an influence decaying rapidly with distance. Moreover, through the cluster expansion, this locality extends to observables, implying that local expectation values can be approximated from local data with controlled accuracy. We exhibit three regimes admitting strong injectivity: random Gaussian PEPS with large physical dimension, high-temperature Gibbs states of commuting two-body
Hamiltonians, and fixed-depth
quantum circuits subject to sufficiently strong depolarizing noise. Our bounds are worst-case sufficient conditions and do not identify sharp algorithmic transitions.
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All authors Siddhant Midha, Yifan F. Zhang, Daniel Malz, Dmitry A. Abanin, Sarang Gopalakrishnan
Quantum Gases · Cross-listed from quant-ph
Dual-use quantum hardware for quantum resource generation and energy storage
Vaibhav Sharma, Yiming Wang and Shouvik Sur
Efficient generation of
quantum resources is a central objective of modern
quantum technological platforms. Independently,
quantum batteries have emerged as nanoscale devices that utilize collective
quantum effects to store energy with a charging advantage over classical strategies. Here, we show a direct connection between these two pursuits: protocols for fast generation of resourceful
quantum states can simultaneously charge a
quantum battery with a collective advantage, and conversely, a
quantum battery protocol with a charging advantage rapidly produces resource-rich states. Using this connection, we propose an integrated hardware protocol on superconducting
circuits in which each experimental run can interchangeably accomplish either
quantum battery charging, or
quantum sensing through generation of metrologically useful states. Our results establish that
quantum resources and stored energy are distinct yet simultaneously-producible quantities within the same dynamics. This opens the door to polymorphic
quantum architectures that dynamically switch between sensing and energy-storage functions, thereby producing additional functionalities without extra hardware cost.
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Mesoscale and Nanoscale Physics
Cryogenic shock exfoliation for ultrahigh mobility rhombohedral graphite nanoelectronics
Ludwig Holleis, Youngjoon Choi, Canxun Zhang et al. (+16 more)
Rhombohedral multilayer
graphene (RMG) offers a highly tunable platform for correlated electron physics, featuring field-effect control of
magnetic, superconducting, and topological phases[1-24]. The promise of these materials has been held back by the limited abundance of rhombohedral stacking in natural graphite, which constrains both sample yield and useful area. Here we introduce 'cryogenic shock exfoliation' to produce large area rhombohedral
graphene flakes which, combined with a low-pressure van der Waals assembly technique that preserves stacking order, enable highly uniform devices exceeding 1300 $\mu m^2$ with fabrication yields of 90%. Using scanning nanoSQUID-on-tip imaging, we demonstrate uniform
spin magnetism over the full central 10 times 10 $\mu m^2$ area of our devices. Transverse
magnetic focusing reveals a disorder mean free path exceeding 200 $\mu m$ at low temperatures. Within the flat surface bands of RMG[20], we observe a size-driven crossover from Poiseuille to porous electron flow in the intermediate-temperature regime of strong electron-electron hydrodynamics[16, 25], providing a further signature of ultrahigh device quality. Our approach overcomes a key materials bottleneck in the fabrication of mesoscopic rhombohedral
graphene devices, paving the way for incorporating strongly correlated phases into two-dimensional nanoelectronics.
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All authors Ludwig Holleis, Youngjoon Choi, Canxun Zhang, Jack H. Farrell, Gabriel Bargas, Audrey Hsu, Zexing Chen, Ian Sackin, Wenjie Zhou, Yi Guo, Thibault Charpentier, Yifan Jiang, Benjamin A. Foutty, Aidan Keough, Martin E. Huber, Takashi Taniguchi, Kenji Watanabe, Andrew Lucas, Andrea F. Young
Superconductivity
$3d_{z^2}$ orbital delocalization and magnetic collapse in superconducting (La,Pr)$_3$Ni$_2$O$_{7-\delta}$ films
Xiaoyang Chen, Wenliang Zhang, Fei Peng et al. (+20 more)
The recent discovery of Ruddlesden–Popper (RP) nickelate thin-film
superconductors has opened a new frontier in unconventional superconductivity. Its realization requires both compressive epitaxial strain and highly oxidative growth conditions, yet the microscopic pathway from the parent phase to the superconducting phase remains elusive. Here, X-ray absorption spectra and resonant inelastic X-ray scattering are employed to track this
evolution by independently tuning strain and oxygen content in (La,Pr)$_3$Ni$_2$O$_{7-\delta}$ thin films. We uncover a remarkable two-step narrative. First, signatures of delocalization emerge in the same way upon two independent tunings: Spectral weight transfers from a ”Upper Hubbard”-like peak to the hole-like peak associated with O $2p_z$ state, and in parallel, the initially localized Ni $3d_{z^2}$ orbital becomes more itinerant followed by the broadening and weakening of $dd$ orbital excitations. Second, as itinerancy increases, long-range
spin-density-wave (SDW) order is suppressed in both intensity and correlation length, indicating direct competition with superconductivity. Yet, short-range
magnons persist: they become damped but their bandwidth stays unchanged. Our results paint a coherent picture that both strain and oxygenation drive the RP
bilayer nickelates towards the superconducting instability, where the O $2p_z$ and Ni $3d_{z^2}$ orbitals become delocalized. Concomitantly, the long-range
magnetic order loses coherence and gets suppressed. These findings establish an orbital-selective route to RP nickelate superconductivity, in which the delocalization of the $2p_z$ and $3d_{z^2}$ orbitals and the robust short-range
magnons upon the melting of SDW order are prerequisites, providing strong constraints for theory and the roadmap for designing nickelate
superconductors.
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All authors Xiaoyang Chen, Wenliang Zhang, Fei Peng, Ting Cui, Guangdi Zhou, Zezhong Li, Jaewon Choi, Lizhi Xu, Yiu-Fung Chiu, Stefano Agrestini, Sahil Tippireddy, Haoliang Huang, Heng Wang, Xianfeng Wu, Peng Li, Jin-Feng Jia, Mirian Garcia-Fernandez, Yi Lu, Er-Jia Guo, Qi-Kun Xue, Zhuoyu Chen, Donglai Feng, Ke-Jin Zhou
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Enhancing Coherence of Spin Centers in p-n Diodes via Optimization Algorithms
Jonatan A. Posligua, David E. Stewart and Denis R. Candido
Solid-state
spin defects hold great promise as building blocks for various
quantum technologies.
Embedding spin centers in $p$-$n$ diodes under reverse bias has proved to be a powerful strategy to narrow the optical linewidth and increase
spin coherence, while also enabling control of the photoluminescence wavelength via Stark shift. Given the multitude of parameters influencing
spin centers in diodes (e.g., doping densities and profiles, temperature, bias voltage,
spin center position), a question that has not yet been answered is: which set of these design parameters maximizes
spin center coherence? In this work, we address this question by developing a scaled gradient descent optimization
algorithm that minimizes the optical linewidth of
spin centers by combining the numerical solution of a diode's Poisson equation with calculated charge noise from the non-depleted regions. Our optimization is performed for both single- and multiple-parameter cases for divacancies in SiC $p$-$i$-$n$ diodes, including reverse-bias voltage, doping density and profile, and diode total length. Importantly, the optimization is subject to realistic physical constraints, such as small operating bias voltages, avoidance of the dielectric breakdown regime and physical thresholds for doping density. Additionally, due to the leakage current at reverse bias voltages, we develop a new formalism to investigate its influence on coherence. We show that the corresponding noise can be mitigated by implanting
spin defects away from the diode's surfaces. Our work provides guidance on experimentally relevant diodes for hosting
spin centers with the narrowest optical linewidths and longest coherence times.
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Materials Science
Extending Hamiltonian-Adaptive Resolution Simulation to Interfaces: An Updated LAMMPS Implementation and Application to Porous Solids
Hari Haran Sudhakar, Alessandra Serva and Rocio Semino
Many natural phenomena involve processes that happen simultaneously at different characteristic length- and timescales. Typically, the region where the process of interest happens is affected by fluctuations in its surroundings. Modeling these systems requires an effective combination of simulation resolutions. The
Hamiltonian-Adaptive Resolution Simulation (H-AdResS) method allows to model dual-resolution systems in length- and time-scales compatible with molecular
diffusion, by combining atomistic and particle-based coarse graining models in the same simulation box. In this work, a new implementation of H-AdResS is provided in LAMMPS 2023. New features extend the usage to more diverse interaction potentials and simplify the preparation of input files via dedicated lammps input commands, while keeping the efficiency gain of the basis method. The implementation is benchmarked by reproducing water properties from a reference atomistic simulation. Importantly, the new implementation includes changes in compensation routines allowing to simulate systems with fluctuating density. As an example, the method in its new implementation is applied to modeling a porous metal-organic framework and its gas adsorption structure and transport properties. We demonstrate that structural and dynamic properties in the atomistic region of the dual-resolution scheme are unaffected and remain those of the fully atomistic system, while increasing simulation efficiency. This paves the way for using H-AdResS to simulate complex interfaces across applications in energy storage, electrocatalysis, and membrane technologies.
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Mesoscale and Nanoscale Physics
Bismuth Films on EuO(111) as a Platform for Proximity-Induced Topological States
Subham Naskar and Sujit Manna
Interfacing two-dimensional bismuth with a
magnetic layer provides a promising route towards realizing higher-order topological phases. In particular, bismuthene on a
ferromagnetic insulator substrate has been theoretically proposed by \citet{Chen2020} as a universal platform for
magnetic second-order topological
insulators. Here, we report the experimental realization of epitaxial bismuth films grown on the
ferromagnetic insulator EuO(111). Using high-resolution scanning tunneling microscopy, we observe atomically ordered bi-layer bismuth with a (012)-oriented quasi-square
lattice, corresponding to a stabilized $\alpha$-phase bismuthene. The resulting film is exceptionally flat compared to conventional metallic films, reflecting the intrinsic two-dimensional nature of the Bi(012) phase. Tunneling spectroscopy(STS) reveals a robust energy gap of about 400 meV in the local density of states, consistent with a
quantum spin Hall insulating phase persisting up to room temperature. Spatially resolved STS further identifies enhanced edge-localised states at the island boundaries. Complementary low-temperature magnetotransport measurements on proximity-coupled ultrathin Bi films exhibit linear magnetoresistance and a
Hall sign reversal, indicative of
quantum-confinement-driven surface-dominated transport. Our results establish bismuthene-
magnetic-
insulator heterostructures as a viable experimental platform for realizing magnetically tunable topological phases, providing a critical step toward the observation of higher-order
topology in two dimensions.
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Materials Science
OptiMat Alloys: a FAIR, living database of multi-principal element alloys enabled by a conversational agent
Yang Hu and Vladyslav Turlo
The FAIR principles have transformed how computational data and workflows are shared in materials research, yet existing repositories can only serve pre-computed entries – broad coverage is perpetually incomplete and cannot adapt to new questions on demand. To address these challenges, we present OptiMat
Alloys, a large
language model-powered conversational
agent for multi-principal element
alloy exploration built on three pillars: a living database that stores every calculation with provenance, low-barrier accessibility through a web interface requiring zero programming expertise, and built-in uncertainty quantification via cross-potential and cross-configuration validation. Coupling foundational machine learning interatomic potentials covering near-all periodic table of elements with natural-
language interaction, OptiMat
Alloys enables targeted, on-demand computation guided by the user's domain knowledge-extending FAIR from pre-computed repositories to on-demand knowledge generation and making computational
alloy screening accessible to any materials scientist.
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Materials Science
Critical role of phase-dependent properties in modeling photothermal sintering of LiCoO2 cathodes
Yang Hu, Benoit Sklénard, Wouter Vels et al. (+2 more)
Photothermal (photonic) sintering crystallizes as-deposited amorphous LiCoO2 (LCO) cathodes for solid-state thin-film batteries using millisecond, surface-localized heating. However, process design often relies on 1D models with phase-averaged, temperature-independent properties, which can mispredict peak temperatures and thermal damage margins. Here we develop a multiscale, data-driven framework that provides phase- and grain size-resolved thermophysical inputs for stoichiometric LCO. We train an Allegro neural network potential with near-ab initio accuracy, enabling Green-Kubo calculations of thermal conductivity for crystalline and amorphous phases. The low, weakly density-dependent conductivity of amorphous LCO motivates its use as an effective intergranular phase in a thin-interface model that reproduces observed grain-size-dependent thermal transport. Combined with measured wavelength-resolved optical properties in 1D multiphysics simulations, we show amorphous LCO absorbs more strongly and reaches higher peak temperatures than crystalline LCO; thus crystalline, constant-property models systematically overestimate safe operating windows.
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All authors Yang Hu, Benoit Sklénard, Wouter Vels, Yaroslav E. Romanyuk, Vladyslav Turlo
Quantum Gases · Cross-listed from quant-ph
Robust continuous symmetry breaking and multiversality in the chiral Dicke model
Nikolay Yegovtsev, Sayan Choudhury and W. Vincent Liu
The Dicke model (DM) serves as a paradigm for understanding collective light-matter interactions. We introduce the
chiral Dicke model, a generalization where an atomic ensemble couples to a two-mode cavity via
chiral interactions. Unlike the standard DM, the
chiral DM is endowed with an inherent continuous $U(1)$
symmetry associated with angular momentum conservation. The ground-state phase diagram and the associated
quantum phase transitions are charted out, revealing a $U(1)$-broken superradiant phase that spans a broad parameter space. We demonstrate that the spectrum of
quantum fluctuations is highly tunable in both the symmetric and broken phases. Strikingly, our calculations reveal that the system exhibits `multiversality', where distinct universality classes govern the transition between the same two phases. In particular, along a special line in parameter space, the dynamical critical exponent for the normal-superradiant phase transition changes from $z\nu=1$ to $z\nu=1/2$. Our work establishes the
chiral Dicke model as a powerful platform to realize novel
quantum phases and multiversal critical phenomena in light-matter coupled systems.
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Materials Science
Modeling High Entropy Alloys' Mechanical Property through Natural Language-Derived Descriptors
Li-Cheng Hsiao, Zi-Kui Liu and Wesley Reinhart
Processing treatments of
alloys, despite being influential to
alloy properties, are often neglected in machine-learning aided
alloy designs due to the difficulties in expressing this information. We investigated the expressiveness of
transformer embeddings through synthesized annealing processing treatment text and verified that
embeddings could be utilized to reconstruct the processing parameters of
alloys effectively with an R2>0.99. We then utilized the vector representations of
alloys' processing treatment descriptions as descriptors to model high-
entropy alloys' hardness and achieved a 20% improvement in prediction, verifying that natural
language-derived descriptors of processing treatment information could be utilized to improve prediction of
alloy properties.
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Materials Science
Sign-resolved nanoscale readout and control of hidden antiferromagnetic spin order
A. Schmid, D. Siebenkotten, D. Dai et al. (+16 more)
Antiferromagnetic memories promise ultrafast, stray-field-free information storage. Yet perfect
magnetic compensation conceals the information carrier itself: the sign of the Néel vector distinguishing two time-reversed states. Moreover, in future dense
memories, the local polarity of Néel domains would need to be read out on the nanoscale. We make this hidden polarity visible in a fully-compensated, high-Néel-temperature, PT-symmetric antiferromagnet by driving interband electric-dipole transitions by mid-infrared near-fields confined at a scanning probe. The excitation generates a Néel-order-dependent
quantum-metric photocurrent, a
Hall-like signal reversing with Néel order, which we term the optical nonlinear anomalous
Hall effect. This optically induced electrical readout maps opposite Néel polarities with sub-100-nm resolution at room temperature and, combined with
spin-orbit-torque writing, reveals Néel-texture polarization and reversible domain-wall motion, establishing electrical-write/optoelectronic-read
antiferromagnetic functionality.
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All authors A. Schmid, D. Siebenkotten, D. Dai, J. Godinho, T. Ostatnický, N. Zou, Y. Zhang, J. Železný, Z. Šobáň, F. Křížek, V. Novák, S. Fairman, A. Hoehl, A. Hertwig, T. Janda, M. A. Huber, R. Huber, B. Kästner, J. Wunderlich
Materials Science
Electronic and Vibrational Properties of On-Surface Synthesized Gulf-Edged Chiral Graphene Nanoribbons
Xuanchen Li, Amogh Kinikar, Vikas Sharma et al. (+8 more)
On-surface synthesis enables
graphene nanoribbons (GNRs) with atomic precision, but the structural diversity of
chiral GNRs remains constrained by the limited range of precursor architectures. Here, we design a trisnaphthalene-based diiodo precursor and use it to synthesize a gulf-edged (4,2,7)-chGNR on Au(111). Scanning tunneling microscopy and bond-resolved non-contact atomic force microscopy establish the atomically precise ribbon structure, while scanning tunneling spectroscopy and periodic density functional theory calculations identify a closed-shell semiconducting state with an experimental band gap of 1.8 eV. Raman spectroscopy, supported by vibrational calculations, resolves a mode localized predominantly at the gulf-edge C-H groups and reveals rapid spectral degradation following air exposure. These results demonstrate a precursor-design concept for a distinct chGNR architecture and correlate its atomic structure with its electronic, vibrational, and environmental-response properties.
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All authors Xuanchen Li, Amogh Kinikar, Vikas Sharma, Andres Ortega Guerrero, Riya Sebait, George F. S. Whitehead, Mickael Lucien Perrin, Carlo A. Pignedoli, Roman Fasel, Ashok Keerthi, Gabriela Borin Barin
Materials Science
Direct observation of surface bandgap shrinkage and negative electronic compressibility in SrTiO3
Warakorn Jindata, Trung-Phuc Vo, Chutchawan Jaisuk et al. (+4 more)
In this work, we investigate and compare the electronic structures of SrTiO3 and KTaO3 under ultraviolet (UV) light induced electron doping. Using angle-resolved photoemission spectroscopy (ARPES), the
evolution of the surface electronic structures of SrTiO3 and KTaO3 is systematically examined as a function of electron density. In contrast to KTaO3, SrTiO3 exhibits a pronounced shrinking of its surface bandgap by approximately 390 meV, accompanied by a counterintuitive shift of the valence band peak toward lower binding energies of up to 200 meV with increasing electron density. This anomalous behavior constitutes a spectroscopic signature of negative electronic compressibility (NEC). Density-functional-theory calculations provide qualitative support for the experimental observations. The calculations show that surface formation already reduces the apparent near-gap separation in SrTiO3, while additional electron accumulation further drives the slab toward a more metallic state; oxygen-vacancy models likewise produce strong bandgap reduction, identifying plausible mechanisms contributing to the observed surface bandgap shrinkage. These findings establish a direct spectroscopic link between bandgap engineering and the NEC effect at the SrTiO3 surface, highlighting the potential of SrTiO3 for next-generation
oxide electronic, optoelectronic, and high-performance capacitive energy storage devices applications.
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All authors Warakorn Jindata, Trung-Phuc Vo, Chutchawan Jaisuk, Sung-Kwan Mo, Thanh-Tien Nguyen, Ján Minár, Worawat Meevasana
Materials Science
Nearly Complete Charge–Spin Conversion via Strain-Eliminated Fermi Pockets in $d$-Wave Altermagnets
Wancheng Zhang, Fangqi Liu, Yong Liu et al. (+4 more)
Ideal $d$-wave altermagnets with nearly orthogonal flat
Fermi surfaces enable complete
spin-channel separation and 100% theoretical charge–
spin conversion efficiency (CSE). The metallic altermagnet $\mathrm{KV_2Se_2O}$ exemplifies this, but realistic samples host residual elliptical
Fermi pockets that enhance charge conductivity while suppressing
spin conductivity, drastically reducing CSE. Here we show that in-plane equibiaxial tensile strain systematically eliminates these parasitic pockets, restoring the flat-band geometry. Our first-principles calculations reveal that CSE increases monotonically with strain, reaching a record $\sim$96% at 4% strain. An effective tight-binding model confirms that pocket suppression, governed by reduced next-nearest-neighbor hoppings, is the dominant mechanism. We further identify an unconventional out-of-plane
spin current component with CSE $\sim$55% at optimal orientations, enabling field-free perpendicular magnetization switching. Moreover, the same strain-driven removal of parasitic pockets yields
giant TMR enhancement in $\mathrm{KV_2Se_2O}$-based
magnetic tunnel junctions, from $10^{5}%$ to $10^{9}%$, and the
giant TMR persists over a wide energy window near the
Fermi level. These findings establish strain engineering as a clean, widely applicable strategy to maximize CSE and magnetoresistance in $d$-wave altermagnets, and provide predictive descriptors for screening high-efficiency spintronic materials.
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All authors Wancheng Zhang, Fangqi Liu, Yong Liu, Jingguo Hu, Zhihong Lu, Rui Xiong, Zhenhua Zhang
Materials Science
Amorphous Nanoconfinement Enables Self-sustaining Sabatier Reaction at Ambient Conditions
Zhiyong Qiu, Cheng Li, Jinzhen Yang et al. (+9 more)
The Sabatier reaction, the catalytic hydrogenation of CO2 into CH4, offers a cornerstone for carbon capture and utilization, and in-situ resource utilization during space exploration; however, it faces a fundamental thermodynamic-kinetic paradox: although highly exothermic, conventional catalysts still require continuous external heating to activate CO2 and maintain stable operation. Here we report an amorphous silica-embedded ruthenium catalyst that enables a long-term self-sustaining autothermal Sabatier reaction dispensing with external energy supply. Operating under ambient conditions, this system achieves a record-high CH4 yield of 0.50 mol gcat-1 h-1 with 100% selectivity, stable operation for over 2,000 hours, and a record-low catalyst bed temperature down to 100 oC. This exceptional self-sustaining behavior stems from the synergistic effect of the catalyst's ultralow effective thermal conductivity (0.27 W m-1 K-1), induced by amorphous nanoconfinement, and its superior intrinsic activity. This synergy generates localized hot spots at Ru sites while suppressing macroscopic heat loss. In situ measurements further reveal CH4 formation even at 54 oC and identify a *CO-mediated pathway for CO2 methanation. The reaction ignites readily with a lighter or focused sunlight and persists even under forced convection from an electric fan, demonstrating strong environmental tolerance. By removing the need for constant energy input, this "ignite-and-forget" system paves the way for decentralized Power-to-Gas systems and autonomous fuel production in resource-constrained environments like Mars.
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All authors Zhiyong Qiu, Cheng Li, Jinzhen Yang, Fangkun Sun, Zheng Zhang, Canwen Yu, Weizheng Cai, Liang Guo, Yutong Gong, Junjie Wang, Meng Danny Gu, Jiazhen Wu
Other Condensed Matter
Physics of Computation and Behavior in Plants
Yasmine Meroz
Plants solve complex problems without centralized control, relying instead on growth-driven dynamics to sense, navigate, and optimize resource acquisition. This review presents a unified physical framework for understanding plant behavior through three complementary principles: distributed physical computation,
embodied mechanical intelligence, and functional stochasticity. Tropic responses and circumnutations are interpreted as spatio-temporal dynamical systems in which information is encoded in biochemical and mechanical fields, integrated over space and time, and translated into differential growth. Mechanical interactions couple morphology to environmental constraints, enabling computation through material properties.
Stochastic fluctuations, from molecular to organismal scales, act as functional resources that enhance sensing, exploration, and collective organization. Together, these processes position plants as a model system for decentralized computation in active matter, where behavior and structure emerge from the interplay of growth, transport, mechanics, and noise.
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Statistical Mechanics
Novel dynamics for an inertial polar tracer in an active bath
Jing-Bo Zeng and Ji-Hui Pei
A polar tracer immersed in an active bath is known to be propelled forward and therefore activated. Here we report that the induced dynamics of an inertial tracer can be much richer than expected. We investigate a heavy polar tracer immersed in a bath of independent active Brownian particles. Using the projection-operator formalism to integrate out the bath, we show that the tracer's reduced dynamics can be precisely mapped onto a
stochastic Lorenz equation. According to the attractors in the Lorenz equation, the tracer motion is classified into several different dynamical regimes, including active Brownian motion,
chiral active Brownian motion, complex chaotic motion, and zigzag active Brownian motion. For certain regimes, we derive analytical expressions for the propulsion speed, the velocity covariance, and the effective
diffusion coefficient. Numerical simulations corroborate these theoretical predictions.
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Materials Science
Neural surrogates for crystal growth dynamics with variable supersaturation: explicit vs. implicit conditioning
Matteo Rigoni, Daniele Lanzoni, Francesco Montalenti et al. (+1 more)
Simulations of
crystal growth are performed by using Convolutional Recurrent Neural Network surrogate models, trained on a
dataset of time sequences computed by numerical integration of Allen-Cahn dynamics including faceting via kinetic anisotropy. Two network architectures are developed to take into account the effects of a variable supersaturation value. The first infers it implicitly by processing an input mini-sequence of a few
evolution frames and then returns a consistent continuation of the
evolution. The second takes the supersaturation parameter as an explicit input along with a single initial frame and predicts the entire sequence. The two models are systematically tested to establish strengths and weaknesses, comparing the prediction performance for models trained on
datasets of different size and, in the first architecture, different lengths of input mini-sequence. The analysis of point-wise and mean absolute errors shows how the explicit parameter conditioning guarantees the best results, reproducing with high-fidelity the ground-truth profiles. Comparable results are achievable by the mini-sequence approach only when using larger training
datasets. The trained models show strong conditioning by the supersaturation parameter, consistently reproducing its overall impact on growth rates as well as its local effect on the faceted morphology. Moreover, they are perfectly scalable even on 256 times larger domains and can be successfully extended to more than 10 times longer sequences with limited error accumulation. The analysis highlights the potential and limits of these approaches in view of their general exploitation for
crystal growth simulations.
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All authors Matteo Rigoni, Daniele Lanzoni, Francesco Montalenti, Roberto Bergamaschini
Materials Science
Nickel intercalation in epitaxial graphene on SiC(0001): a novel platform for engineering two-dimensional heterostructures
Ylea Vlamidis, Stiven Forti, Antonio Rossi et al. (+5 more)
Two-dimensional (2D)
magnetic materials integrated with
graphene offer a compelling platform for next-generation spintronic devices, yet nickel in its 2D form remains largely unexplored, due to fundamental synthesis limitations. Here, we report the controlled intercalation of Ni beneath epitaxial
graphene on the Si-face of SiC(0001), achieved through a scalable colloidal nanoparticle deposition route. Chemically synthesized Ni nanoparticles (~10 nm diameter) are uniformly deposited onto
graphene via immersion in colloidal solution at room temperature; subsequent thermal annealing at 650 {\deg}C drives intercalation, yielding well-ordered Ni islands at the
graphene/buffer-layer interface with morphology dictated by annealing conditions. Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), supported by density functional theory (DFT) calculations, elucidate the atomic and electronic structure of the intercalated layers. DFT simulations further confirm the thermodynamic stability of the 2D nanostructures as a function of shape and lateral size, predicting a robust average
magnetic moment of 0.9 $\mu_B$ per atom. The resulting Ni-intercalated
graphene on SiC constitutes a well-defined 2D
heterostructure combining preserved
graphene band structure with robust interfacial magnetism, stable under ambient conditions. These findings establish a reproducible, scalable pathway to engineer
magnetic graphene-based
heterostructures and open new avenues for their integration into spintronic architectures.
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All authors Ylea Vlamidis, Stiven Forti, Antonio Rossi, Arrigo Calzolari, Carmela Marinelli, Camilla Coletti, Stefan Heun, Stefano Veronesi