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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 31 March

Materials Science · Cross-listed from gr-qc

Mexican Burrowing Toads as gravitational wave detectors

Frederic V. Hessman and Christian Jooss

It is generally assumed that gravitational waves are extremely difficult to detect. However, we show that the call of the Mexican Burrowing Toad has an amazing resemblance to cosmic gravitational wave signals due to the merging of neutron stars and/or black holes. It is known that toads exhibit magnetoreception - the ability to detect magnetic fields - and that magnetic fields thus subtly affect ion channel activities in toad neurons. We speculate that gravitational strains produce phonons and magnons in a ferromagnetic substance embedded in the nervous system of the toads and that these coherent signals are exponentially amplified by a Raman laser mechanism to the point where they can be detected. The fine tuning necessary for this mechanism to work would help to explain why this species of toad show this remarkable ability and others do not. We analyze the sound of a pond full of Mexican Burrowing Toads in the hopes of detecting slight phase shifts in their calls due to a gravitational wave event. No effect was found and the the LIGO/VIRGO consortia have not reported an event during the recording, illustrating the power of this approach. We suggest the massive use of these toads would be an inexpensive way to support the operation of optical interferometric gravitational wave detector facilities.
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Materials Science

Machine Learning Assisted Reconstruction of Local Electronic Structure of Non-Uniformly Strained MoS2

Soumyadip Hazra, Sraboni Dey, Arijit Kayal et al. (+3 more)

Wrinkles and nanobubbles are an integral and often unavoidable part of integrating 2D van der Waals semiconductors into actual device architectures. Despite their ubiquitous nature, quantitative correlation between such spatially non-uniform strain and modifications to the local electronic structure remains challenging. Here, density functional theory is combined with a recurrent neural network to reconstruct the local electronic structure of monolayer MoS2 from strain maps derived from atomic force microscopy (AFM) topography and Raman spectral maps. The analysis reveals that biaxial bending induced strain is significantly more effective than both uniaxial bending or in-plane strain in modifying electronic and dielectric properties. A ~ 0.35% strain induced by biaxial bending results in ~ 22% reduction in band gap and ~ 7% increase in dielectric constant, compared to a ~ 5% reduction in band gap and ~ 1% increase in dielectric constant under comparable uniaxial bending. The modified band structure reveals band edge states that concentrate charge in regions of high curvature or strain. While conductive AFM measurements indicate increased local conductance (carrier density) at wrinkles and nanobubbles, the spatial band gap maps predicted by the model are validated against experimental photoluminescence peak energy maps. The results indicate that strained features like wrinkles and nanobubbles commonly present in real devices influence the band gap, carrier distribution, and dielectric response, which favourably affects electrical transport in such systems. The framework developed here can be readily extended to other 2D materials and heterostructures, offering a computationally efficient route for studying and exploiting strain effects.
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All authors Soumyadip Hazra, Sraboni Dey, Arijit Kayal, Narendra Shah, Renjith Nadarajan, Joy Mitra

Strongly Correlated Electrons · Cross-listed from hep-ph

Entanglement in the $\theta$-vacuum

Sebastian Grieninger, Dmitri E. Kharzeev and Eliana Marroquin

We compute the entanglement entropy and the entanglement spectrum of the vacuum state in the massive Schwinger model at a finite $\theta$ angle. By computing two-point correlation functions we show that the correlation length diverges in the critical region. We clarify the physical origin of entanglement entropy enhancement at $\theta=\pi$ by relating it to the competition between distinct electric-flux vacuum branches. We show that the peak near $\theta=\pi$ persists across the range of masses studied and corresponds to the point of maximal competition between distinct vacuum branches with opposite electric-field orientation, where quantum fluctuations due to fermion pair creation are maximized. While this entropy enhancement is generic, a pronounced compression of the low-lying entanglement spectrum at $\theta=\pi$ distinguishes the near-critical case ($m/g\simeq0.33$). Using the Bisognano–Wichmann (BW) theorem, we construct a lattice BW entanglement Hamiltonian and compare it with the exact modular Hamiltonian obtained from the reduced density matrix. We observe agreement in the infrared sector, indicating that the entanglement Hamiltonian is well approximated by a spatially weighted Hamiltonian. Finally, we discuss possible applications to entanglement in topological insulators and quantum wires. In this work, we used the chirally rotated formulation of the Schwinger model Hamiltonian. We identify an additive vacuum-energy artifact induced by the discretization of the chirally rotated lattice and derive its exact free-lattice form to subtract it in the continuum limit.
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Materials Science

Atomically Reconfigurable Single-Molecule Optoelectronics

Atif Ghafoor, Santeri Neuvonen, Thinh Tran et al. (+6 more)

Deterministic control of excitonic properties is key to advancing nanoscale optoelectronic and quantum technologies and to understanding diverse physical, optical, chemical, and biological phenomena. At the molecular scale, these properties can be tuned through chemical modification, local-environment influence or charge-state manipulation. Yet, direct control of a molecule's transition dipole moment and its resulting light emission via atomic-scale structural modification has remained elusive. Here, using scanning tunnelling microscopy-induced luminescence, we show that a single structural parameter-the vertical displacement of the central metal atom in a planar phthalocyanine molecule on a decoupling layer-enables active tuning of the transition dipole, allowing either suppression or enhancement of emission. Exploiting this control, we realized a tunable homodimer switchable among three optical states: non-emissive, single-molecule-like emissive, and coupled states exhibiting subradiant and superradiant modes, directly revealing intermolecular dipole-dipole coupling. We further demonstrate a heterodimer in which resonant energy transfer can be turned on or off simply by controlling the acceptor's transition dipole moment. These findings not only establish atomic-scale displacement as a general strategy for optical molecular switching, but also demonstrate the reconfigurable engineering of excitonic interactions within molecular assemblies.
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All authors Atif Ghafoor, Santeri Neuvonen, Thinh Tran, Oscar Moreno Segura, Yitao Sun, Yaroslav Pavlyukh, Riku Tuovinen, Jose L. Lado, Shawulienu Kezilebieke

Mesoscale and Nanoscale Physics

Thermodynamic Multipoles and Dissipative Conductivities in Metallic Systems

Takumi Sato and Satoru Hayami

Multipoles provide a systematic framework for describing the electronic structures of quantum materials from a symmetry perspective. Thermodynamic multipole moments in crystalline solids exhibit direct microscopic connections to certain allowed physical responses beyond symmetry; however, such relations have thus far been limited to dissipationless responses in equilibrium insulating systems. Here, this framework is extended at a heuristic level by focusing on the Fermi-surface contributions to thermodynamic multipole moments. These contributions establish direct relations to dissipative transport responses characteristic of metals, including charge and spin conductivities. A key consequence is that the conductivities exhibit extrema, typically maxima, at chemical potentials where the corresponding Fermi-surface contributions to the multipoles vanish, specifically, the electric quadrupole for charge conductivity and the magnetic octupole for spin conductivity. These findings uncover a previously overlooked aspect of thermodynamic multipole moments, opening a new perspective on dissipative transport in metallic systems.
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Statistical Mechanics

Mean first passage times of higher-dimensional velocity jump processes

Maria R. D'Orsogna, Alan E. Lindsay and Thomas Hillen

First passage phenomena arise across physics, biology, and finance when stochastic processes first reach a threshold, triggering downstream events. Examples include the irreversible exit from a domain, a biochemical reaction, a financial selloff. While typical formulations involve diffusive motion, many stochastic processes are better described as velocity jump processes, characterized by persistent motion interrupted by stochastic velocity changes. Despite their ubiquity, first-passage properties of velocity jump processes remain underdeveloped in higher dimensions, especially under directional bias. We present a general framework to estimate the mean first passage time (MFPT) and higher moments of the survival probability for fixed-speed velocity jump processes where possible reorientations range from strong alignment to full angular anisotropy. For low Knudsen numbers, when the mean free path is small compared to the distance to the target, we derive a universal form for the MFPT in which two bias functions encode broad classes of angular distributions, including von Mises-Fisher, wrapped Cauchy, and elliptical families. In the narrow capture limit of a vanishingly small target, directional persistence induces anomalous scaling, including regimes where the MFPT remains finite whereas standard diffusion would predict divergence. Finally, we obtain a Langevin representation that accurately reproduces first-passage statistics. Analytical predictions are confirmed by numerical simulations.
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Mesoscale and Nanoscale Physics

Spatiotemporal imaging of gate-controlled multipath dynamics of fractional quantum Hall edge excitations

Yunhyeon Jeong, Akinori Kamiyama, John N. Moore et al. (+6 more)

Quantum Hall edge excitations, whose low-energy behavior admits a chiral conformal-field-theory description, are a promising platform for engineered dynamical experiments, including analog-spacetime proposals. However, establishing their edge dynamics in realistic electrostatic landscapes is essential for controlled dynamical experiments and has remained experimentally challenging. Here we report spatiotemporal imaging of gate-controlled multipath dynamics of edge excitations in a $\nu = 1/3$ fractional quantum Hall device using stroboscopic time-resolved photoluminescence microscopy and spectroscopy with $\sim$100-ps resolution. By tuning a control-gate-defined potential landscape, we observe switching between mesa-defined and gate-defined trajectories and identify an intermediate regime in which a single launched excitation accesses multiple pathways. Time-resolved measurements at downstream locations reveal gate-dependent arrival times and pronounced temporal broadening, showing that the propagation dynamics are strongly modified by the local confinement and become increasingly dispersive in a multipath landscape. We further observe a long-range transverse optical response extending tens of micrometers into the bulk and persisting over distances exceeding 200 $\mu$m downstream, consistent with the near-field component of an edge magnetoplasmon. These results establish direct experimental access to controllable multipath edge dynamics in the fractional quantum Hall regime and suggest a platform for engineered nonequilibrium and interference-based experiments, as well as future analog-spacetime studies in quantum Hall edge systems.
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All authors Yunhyeon Jeong, Akinori Kamiyama, John N. Moore, Takaaki Mano, Ken-ichi Sasaki, Yuuki Sugiyama, Tokiro Numasawa, Masahiro Hotta, Go Yusa

Quantum Gases

Generation of dipolar supersolids through a barrier sweep in droplet lattices

E. L. Brakensiek, G. A. Bougas and S. I. Mistakidis

We propose a dynamical protocol to generate supersolids in dipolar quantum gases by sweeping a repulsive Gaussian barrier through an incoherent quasi-one-dimensional droplet array. Supersolidity is inferred by monitoring the ensuing dynamics of the density, momentum distribution, center-of-mass motion, and superfluid fraction within the framework of the extended Gross-Pitaevskii equation with quantum corrections. A persistent superfluid background arises, atop which the crystals oscillate in unison, indicating the establishment of phase coherence. This process is accompanied by energy redistribution and the gradual transfer of higher-lying momenta toward the zero momentum mode. The dependence of the superfluid fraction on the barrier velocity and height is also elucidated evincing the parametric regions which facilitate the rise of a superfluid background. Our results pave the way for engineering supersolid generation using experimentally accessible protocols.
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Materials Science

Quantum anomalous Hall effect in monolayer transition-metal trihalides

Thi Phuong Thao Nguyen and Kunihiko Yamauchi

We present systematic first-principles results for the electronic and magnetic properties of two-dimensional transition-metal trihalide monolayers MX3 (M = V, Cr, Mn, Fe, Ni, Pd; X = F, Cl, Br, I), focusing on their potential to host the quantum anomalous Hall effect. In particular, MnF3 and PdF3 exhibit a spin-polarized Dirac cone at the K point, spin-orbit coupling opens a sizable gap with a nonzero Chern number. Nanoribbon slab calculations reveal gap-crossing chiral edge states, establishing the nontrivial topological character. Beyond these case studies, our systematic screening clarifies general trends across the MX3 family and provides insight into how electronic configuration and spin-orbit coupling cooperate to produce magnetic and topological phases in two-dimensional magnets.
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Materials Science

Long-range interaction effects on the phase transition, mechanical effect, and electric field response of BaTiO3 by machine learning potentials

Po-Yen Chen and Teruyasu Mizoguchi

Bulk materials are governed by both short-range and long-range interactions, both of which are naturally captured in conventional density functional theory (DFT) calculations through Ewald summation of electrostatic contributions. In contrast, machine learning potentials (MLPs) typically rely on local atomic environment descriptors, and long-range interactions are often neglected. Such approximations may introduce systematic energetic errors and lead to inaccuracies in predicted material properties. To systematically investigate the impact of long-range interactions in ferroelectric BaTiO3 within the framework of MLPs, we developed a long-range MACELES model and compared its performance with the previously reported BaTiO3 MACE model across four key properties (phonon dispersion, phase transition behavior, mechanical response, and ferroelectric properties including dielectric constants). We find that qualitative behaviors, including phase transitions, stress-induced polarization switching, and polarization-electric field hysteresis, are consistently reproduced by both models. In contrast, quantitative properties such as transition temperatures, elastic constants, and dielectric constants exhibit systematic improvements in MACELES model, highlighting the importance of incorporating long-range electrostatics for accurately describing the structural and dielectric responses of BaTiO3. These results suggest that while long-range interactions play a role in improving quantitative accuracy, their omission does not significantly alter the qualitative ferroelectric behavior of BaTiO3.
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Materials Science

Phonon Signatures of Near-Room-Temperature Phase Transition in Quasi-One-Dimensional Bi4I4 Topological van der Waals Material

Nidhish Thiruthukkal Puthenveettil, Topojit Debnath, Clayton Mantz et al. (+7 more)

The quasi-one-dimensional material Bi4I4 hosts two crystallographically similar polymorphs that realize distinct topological insulating phases separated by a first-order structural transition near room temperature. This transition occurs without a change in space group, arising instead from a subtle rearrangement of chain stacking registry. Polarization-resolved Raman spectroscopy directly resolves this structural-topological phase transition through abrupt, hysteretic modifications of the phonon spectrum. Angle-dependent measurements establish the symmetry of the dominant Raman-active modes and require a complex Raman tensor formalism to account for absorption-induced phase effects. Across the transition, selected phonon modes exhibit discontinuous, reversible shifts in frequency, linewidth, and relative intensity despite the absence of a space-group change. Density functional theory calculations reproduce the direction of the observed phonon renormalizations and confirm their sensitivity to stacking-dependent force constants. These results demonstrate that polarization-resolved Raman spectroscopy can detect subtle stacking-driven structural rearrangements that underlie topological band character, even when global crystallographic symmetry remains unchanged. The obtained results provide valuable insights into the interplay among lattice dynamics, structural distortions, and topological properties in this class of low-dimensional materials, with strong potential for unique functionalities.
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All authors Nidhish Thiruthukkal Puthenveettil, Topojit Debnath, Clayton Mantz, Zahra Ebrahim Nataj, Jordan Teeter, Md. Shafayat Hossain, Fariborz Kargar, Tina T. Salguero, Roger K. Lake, Alexander A. Balandin

Mesoscale and Nanoscale Physics

Quantum Fisher information in many-photon states from shift current shot noise

Evgenii Barts, Takahiro Morimoto and Naoto Nagaosa

Quantum Fisher information (QFI) sets the ultimate precision of optical phase measurements and reveals multiphoton entanglement, but it is not accessible with conventional photodetection. We theoretically predict that a photodetector utilizing the shot noise of the quantum-geometric shift current of exciton polaritons can directly measure the QFI of nonclassical light. By solving the Lindblad equation, we obtain the time-dependent nonlinear photocurrent for an arbitrary initial photon state. It turns out that, regardless of the quantum state of the incident light, the integrated current depends only on the mean photon number. In stark contrast, the shot noise retains the quantum information: its Fano factor is proportional to the photon number variance and therefore encodes the QFI. Numerical calculations confirm these relations for illumination with optical Schrödinger cat and squeezed vacuum states. Quantum correlations in nonclassical light, usually hidden from direct detection, become observable in the form of shift current shot noise
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Mesoscale and Nanoscale Physics

Interplay of Quasiperiodicity, Hubbard Interactions, and Staggered Magnetism in a 1D Ring: Localization and Re-entrant Characteristics

Souvik Roy and Ranjini Bhattacharya

We study interaction-induced localization in a spinful quasiperiodic Hubbard ring with quasiperiodically modulated hopping and a staggered spin-dependent Zeeman field using a self-consistent Hartree-Fock approach. We characterize localization through the inverse participation ratio, normalized participation ratio, and multifractal analysis, and further examine its signatures in self-consistent real-space observables, including double occupancy, density fluctuations, local entropy, spin-density-wave order, and related correlation measures. As the Hubbard interaction is increased, we find a nonmonotonic evolution of the eigenstates: an initially extended regime gives way to an intermediate localized phase, followed by reentrant delocalization at stronger interactions. The width of this intermediate regime grows systematically with both the quasiperiodic hopping amplitude and the staggered Zeeman-field strength, indicating a cooperative enhancement of localization by these two ingredients. In the localized regime, the self-consistent interaction produces pronounced spin dependence in both the spectra and localization properties, resulting in distinct responses of the spin-up and spin-down sectors. The interaction-driven crossover is consistently captured by the real-space observables and further corroborated by real-time wave-packet dynamics, which reveal successive ballistic, confined, and reentrant-transport regimes consistent with the underlying eigenstate character. These results provide a unified framework for understanding the interplay of quasiperiodicity, electronic interactions, and spin-dependent fields in controlling localization, criticality, and quantum transport in correlated quasiperiodic systems.
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Materials Science

Role of surface states and band modulations in ultrathin ruthenium interconnects

Gyungho Maeng, Subeen Lim, Mi Gyoung Lee et al. (+3 more)

Mitigating the RC delay from transistor miniaturization is essential for next-generation devices, driving a focus on interconnect electrical performance. Current copper-based interconnects face a critical challenge, that their resistivity sharply increases at the nanometer-scale due to surface and grain boundary scattering. Therefore, there is a pressing need for techniques that reduce resistance in ultrathin metal films. In this study, we employ the density functional theory to investigate how the intrinsic electronic structure of thin films impacts conductivity as a function of thickness. Notably, our analysis of ruthenium slab structures shows that surface states significantly influence thickness-dependent resistivity. It reveals that vacuum-terminated Ru slab exhibits decreasing resistivity with the decrease in thickness, whereas oxygen-terminated Ru slab shows the opposite trend. This difference is fundamentally attributed to the presence or absence of surface states, highlighting the importance of surface engineering in optimizing interconnect performance.
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All authors Gyungho Maeng, Subeen Lim, Mi Gyoung Lee, Bonggeun Shong, Kyeongjae Cho, Yeonghun Lee

Mesoscale and Nanoscale Physics

Quasiperiodicity-Engineered Re-entrant Localization-Delocalization aspects in a Diamond Lattice

Ranjini Bhattacharya and Souvik Roy

We investigate localization in a quasiperiodically engineered diamond lattice with strand-dependent Aubry-André-Harper onsite modulations, highlighting the decisive roles of the modulation ratio $s$ and the averaged potential on the middle strand. The upper strand hosts the primary potential $\lambda$, the lower strand carries a weaker modulation $\lambda/s$, and the middle strand follows their average, generating a correlated quasiperiodic landscape across each plaquette. By tuning $\lambda$ for selected values of $s$, we probe spectral and eigenstate properties via the inverse participation ratio (IPR), normalized participation ratio (NPR), and fractal dimension $D_2$. We uncover a pronounced re-entrant localization behavior, where eigenstates repeatedly switch between extended and localized regimes, which persists only within a finite range of $s$ and crucially relies on the averaged potential construction. This unconventional sequence arises from the interplay of $s$, the correlated potential, and the intrinsic diamond geometry, producing a highly nontrivial interference landscape. Our results reveal localization physics beyond the standard Aubry-André paradigm, further supported by the evolution of extended states, system-size scaling of $\langle \mathrm{NPR} \rangle$ and $\langle D_2 \rangle$, and dynamical signatures from the time-dependent root-mean-square displacement, confirming the robustness of the re-entrant transitions.
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Strongly Correlated Electrons

Three-Band Anderson Lattice Model Reveals Co-Evolution of Topological and Magnetic Phases Driven by Electron Correlation

Zhong-Yi Wang, Ya-Min Quan, Yu-Xuan Sun et al. (+2 more)

Understanding the interplay of band topology, strong electron correlation, and magnetic order is the fundamental core bottleneck for realizing robust high-temperature quantum anomalous Hall effect (QAHE). Conventional two-band Anderson models are limited to paramagnetic Kondo topological insulators, failing to capture coupled topological-magnetic phase evolution relevant to the QAHE benchmark MnBi2Te4 family. We develop a minimal three-band Anderson lattice model incorporating Hubbard interaction, s-d exchange coupling, and a BHZ-like topological mechanism. Using the Kotliar-Ruckenstein slave-boson approach, we map correlation-driven phase transitions at filling v=2: increasing U drives a trivial-to-Kondo topological insulator transition, then activates the third band to mediate a paramagnetic topological insulator-to-ferromagnetic metal transition. The accompanying band reconstruction–fully spin-polarized d-orbitals sinking below the Fermi level, leaving itinerant p-orbitals to dominate low-energy physics–qualitatively matches published first-principles results for MnBi2Te4. In the strong-correlation regime, exchange coupling J stabilizes a Chern-Kondo insulator (C=1) and Weyl nodal-line semimetal. Critically, we reveal full d-orbital spin polarization renders the topological gap immune to correlation-induced narrowing, resolving the long-standing strong correlation-large gap incompatibility. Our results show excellent qualitative alignment with recent state-of-the-art QAHE experiments, providing a unified framework for correlated magnetic topological materials and new pathways to high-temperature QAHE.
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All authors Zhong-Yi Wang, Ya-Min Quan, Yu-Xuan Sun, Liang-Jian Zou, Xiang-Long Yu

Mesoscale and Nanoscale Physics

Interplay of Electric Dipole Spin Resonance and Multilevel Landau-Zener Interference in p-Type Silicon Quantum Dots

Sayyid Irsyadul Ibad, Yusaku Suzuki, Masahiro Tadokoro et al. (+8 more)

In this work, we examine microwave responses of the Pauli spin blockade (PSB) leakage current through a p-type silicon double quantum dot. We observe more than the expected two resonance lines with the main resonance line exhibits both positive and negative peaks as a function of the magnetic field, corresponding to enhancement and suppression of the PSB leakage current, respectively. We attribute the observed spectra to the interplay between two spin rotation mechanisms: spin-orbit-mediated electric dipole spin resonance (EDSR) and multilevel Landau-Zener (MLLZ) interference, both of which are present in electrically driven devices with strong spin-orbit coupling (and enhanced in the vicinity of orbital level crossings). A numerical simulation taking into account both mechanisms show agreement with the experimental results. While these unconventional spectral behaviours can be readily suppressed away from the orbital level crossing or in devices with weak spin-orbit coupling, our study showcases the potential complexity of spin-rotating mechanisms for electrically driven spin qubits.
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All authors Sayyid Irsyadul Ibad, Yusaku Suzuki, Masahiro Tadokoro, Tokio Futaya, Shimpei Nishiyama, Kimihiko Kato, Shigenori Murakami, Takahiro Mori, Raisei Mizokuchi, Jun Yoneda, Tetsuo Kodera

Quantum Gases

Dissipation-induced Nonlinear Topological Gear Switching

Xuzhen Cao, Xiaolin Li, Liang Bai et al. (+3 more)

Nonlinear interaction enables topological phenomena impossible in linear systems. A paradigm is nonlinear Thouless pump, where the transport of solitons can be topologically quantized even when band occupation is nonuniform. Such nonlinear quantization traditionally requires a time-periodic Hamiltonian with static nonlinearity and, much as in the linear case, is inherently independent of pumping speed. Instead, we demonstrate a dissipation-induced topological gear switching, where quantized soliton transport can be switched on and off via the adiabatic pumping speed itself. This phenomenon has no counterpart in prior conservative nonlinear pumps, nor in linear non-Hermitian pumps. Crucially, quantization here no longer requires a time-periodic nonlinear Hamiltonian; it stems from a genuinely non-equilibrium mechanism captured by an effective conservative model whose nonlinearity varies aperiodically in time. Remarkably, a quantized nonlinear transport can be induced even when this nonlinear aperiodic driving is such that the system is pumped from the linear to nonlinear regimes. Our results open a route toward nonequilibrium nonlinear topological matter, where topological effect is dynamically reconfigurable via time-varying nonlinearities, with experimental implications for photonic, atomic, or superconducting platforms and beyond.
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All authors Xuzhen Cao, Xiaolin Li, Liang Bai, Zhaoxin Liang, Li-Chen Zhao, Ying Hu

Materials Science

Robust Flat Magnetoresistivity in D0$_3$-Fe$_3$Ga Driven by Chiral Anomaly

Ruoqi Wang, Xinyang Li, Bo Zhao et al. (+11 more)

Topologically non-trivial nodes emerging from flat-band crossings not only enhance unconventional topological responses but also play a fundamental role in exploring correlation-driven topological physics. Here, we report the exceptionally robust chiral-anomaly-dominated transport in D0_3-Fe_3Ga. First, we observe a combination of positive and negative magnetoresistance, ideal planar longitudinal magnetoresistance (PLMR), and the planar Hall effect (PHE). Second, ultra-low-temperature resistivity exhibits pronounced non-Fermi-liquid (NFL) behavior, accompanied by the emergence of giant intrinsic anomalous Hall conductivity (AHC), in excellent agreement with our DFT calculations, which confirm the existence of tilted Weyl points arising from crossings of nearly three-dimensional (3D) flat bands. Most remarkably, we detect an exceptionally robust flat magnetoresistance (flat-MR) that persists without decay up to 33 T. This set of phenomena provides strong evidence that the Fermi level intersects the flattened Weyl crossings, offering confirmation of a topological flat-band semimetal. D0_3-Fe_3Ga presents a promising magnetic platform for quantum device innovations.
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All authors Ruoqi Wang, Xinyang Li, Bo Zhao, Haofu Wen, Xin Gu, Shijun Yuan, Langsheng Ling, Chuanying Xi, Ze Wang, Kunquan Hong, Liang Ma, Ke Xia, Taishi Chen, Jinlan Wang

Other Condensed Matter

A Unified Theory of Deterministic Magnetic Switching

Xizhi Fu, Lei Han, Xi Liu et al. (+2 more)

The deterministic switching of magnetic order parameters is critically important, as it forms the fundamental basis for manipulating information states in magnetic memory devices. This work presents a general theoretical framework that unifies the mechanisms of magnetic switching by introducing the concept of switching symmetry and establishing that the necessary condition for deterministic switching is the breaking of all switching symmetries, which can be achieved through asymmetric states, asymmetric barriers, and asymmetric torques. Our theory can successfully and universally explain all reported experimental cases of deterministic magnetic switching and provides unified and simple design principles for new switching devices of all magnetic materials without the need of complicated simulations.
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All authors Xizhi Fu, Lei Han, Xi Liu, Cheng Song, Junwei Liu

Mesoscale and Nanoscale Physics

Exploring non-trivial band structure and spin polarizations in $d$-wave altermagnets tailored by anisotropic optical fields

Andrii Iurov, Liubov Zhemchuzhna and Tiyhearah Danner-Jackson

The subject of the present paper is a detailed theoretical investigation of the energy spectrum and bandgaps, as well as topological and collective properties and linear response, in $d$-wave altermagnets in the presence of an off-resonance optical dressing field. We consider the altermagnets with both $d_{x^2-y^2}$ and $d_{xy}$ pairing symmetries and focus on anisotropic dressing fields applied to an anisotropic and non-linear electron Hamiltonian. We have uncovered several crucial properties of the resulting electron-dressed states; specifically, we found that a finite bandgap is opened by linearly polarized irradiation, a phenomenon not observed in Dirac materials. Some of the crucial properties of the electron dressed states in the presence of the linearly polarized light can be uncovered only in the second-order perturbation expansion, which is often omitted. We found that introducing an anisotropic driving field leads to several subtle yet important changes in the Edelstein susceptibilities of altermagents, enabling the fine-tuning of their spin polarizations. We calculate the Berry curvature for various types of altermagnets and obtain closed-form analytical expressions for circularly polarized irradiation. We demonstrate that the optical driving field can generate finite Berry curvature in the absence of altermagnetic order. All these results are expected to become a crucial contribution to the rapidly developing fields of spintronics and device physics.
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Monday 30 March

Materials Science · Cross-listed from physics.chem-ph

Generative Chemical Language Models for Energetic Materials Discovery

Andrew Salij, R. Seaton Ullberg, Megan C. Davis et al. (+5 more)

The discovery of new energetic materials remains a pressing challenge hindered by limited availability of high-quality data. To address this, we have developed generative molecular language models that have been pretrained on extensive chemical data and then fine-tuned with curated energetic materials datasets. This transfer-learning strategy extends the chemical language model capabilities beyond the pharmacological space in which they have been predominantly developed, offering a framework applicable to other data-spare discovery problems. Furthermore, we discuss the benefits of fragment-based molecular encodings for chemical language models, in particular in constructing synthetically accessible structures. Together, these advances provide a foundation for accelerating the design of next-generation energetic materials with demanding performance requirements.
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All authors Andrew Salij, R. Seaton Ullberg, Megan C. Davis, Marc J. Cawkwell, Christopher J. Snyder, Cristina Garcia Cardona, Ivana Matanovic, Wilton J. M. Kort-Kamp

Statistical Mechanics · Cross-listed from quant-ph

Zeno-Constrained Formation of Relativistic Mass Shells

Ansgar Pernice

We study an extension of the quantum linear Boltzmann equation describing irreversible momentum-space dynamics of an open quantum system under strong continuous monitoring. The monitored observable is taken to be a quadratic form in an extended, purely Euclidean four-dimensional momentum space, without assuming any fixed signature at the microscopic level. In the resulting quantum Zeno regime, rapid suppression of off-constraint excursions allows for an adiabatic elimination of fast degrees of freedom. Using a Schur-complement construction, the induced second-order corrections give rise to an effective flow of the monitored quadratic form under temporal coarse graining. Under mild isotropy assumptions on the underlying momentum-mixing dynamics and an appropriate calibration condition, this flow approaches an infrared fixed point characterized by a quadratic form of Lorentzian signature. The corresponding null set defines a mass-shell-like constraint surface that governs the long-time Zeno-projected dynamics and whose isometry group matches the kinematic structure of Lorentz transformations at the effective level. Familiar relativistic features, including Maxwell-Juettner-type stationary distributions, arise at the level of the effective infrared description as consequences of this fixed point within the extended quantum Boltzmann framework.
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Statistical Mechanics

The geometric origin of criticality: a universal mechanism in mean-field rotor Hamiltonians

Loris Di Cairano

We introduce a universal criterion for criticality in mean-field rotor Hamiltonians based on the geometric structure of the constant-energy shell. Rather than characterizing the onset of a phase transition through the conventional thermodynamic singularities alone, we show that the relevant information is already encoded in the way the geometry of the shell reorganizes along distinguished collective directions. For a broad class of finite-dimensional trigonometric mean-field interactions, the trace of the Weingarten operator (representing the principal curvatures) admits a universal collective expansion in terms of the order-parameter amplitudes. This expansion defines an energy-dependent quadratic form whose eigenmodes identify the geometrically unstable channels of the system. Criticality is then associated with the vanishing of the corresponding curvature coefficients, yielding a direct geometric selection principle for the modes that become unstable at the transition. In this way, the phase transition in mean-field systems (usually of first- or second-order) is reformulated as a geometric instability phenomenon intrinsic to the microcanonical energy shell. The resulting framework is geometrically universal within the class considered, independent of model-specific details except for a finite set of collective couplings. Moreover, our approach recovers the known critical channels in standard mean-field rotor models while extending naturally to multimode and spectrally coupled cases. These results support a view in which critical behavior can be understood as reorganizations of energy-shell geometry triggered by a collective restructuring of the underlying energy-shell geometry.
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Statistical Mechanics

How much of persistent homology is topology? A quantitative decomposition for spin model phase transitions

Matthew Loftus

Point-cloud persistent homology (PH) – computing alpha or Rips complexes on spin-position point clouds – has been widely applied to detect phase transitions in classical spin models since Donato et al. (2016), with subsequent studies attributing the detection to the topological content of the persistence diagram. We ask a simple question that has not been posed: what fraction of the PH signal is genuinely topological? We introduce f_topo, a quantitative decomposition that separates the density-driven and topological contributions to any PH statistic by comparing real spin configurations against density-matched shuffled null models. Across the 2D Ising model (system sizes L = 16-128, ten temperatures) and Potts models (q = 3, 5), we find that H_0 statistics – total persistence, persistence entropy, feature count – are 94-100% density-driven (f_topo < 0.07). The density-matched shuffled null detects T_c at the identical location and with comparable peak height as real configurations, showing that density alone is sufficient for phase transition detection. However, H_1 statistics are partially topological: the topological fraction grows with system size as delta(TP_{H_1}) ~ L^{0.53} and follows a finite-size scaling collapse delta(T, L) = L^{0.53} g(tL^{1/nu}) with collapse quality CV = 0.27. The longest persistence bar is strongly topological (f_topo > 1) and scales with the correlation length. A scale-resolved analysis reveals that the topological excess shifts from large-scale to small-scale features as L increases. We propose that the TDA-for-phase-transitions community adopt shuffled null models as standard practice, and that H_1 rather than H_0 statistics be used when genuine topological information is sought.
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Materials Science

Energy level alignment of vacancy-ordered halide double perovskites

Ibrahim Buba Garba and George Volonakis

Vacancy-ordered double perovskites have emerged as lead-free alternatives, offering remarkable stability and compositional tunability for optoelectronic applications. In this study, we provide first-principles insights into their electronic properties, surface stability, and energy level alignment using a non-empirical, dielectric-dependent hybrid functional. For a representative family of Cs$_2$MX$_6$ compounds, with M = Zr, Sn, Te, and X= Cl, Br, I, our calculations reveal that the predicted bulk electronic band gaps are in excellent agreement with those obtained using the state-of-the-art GW method, validating the accuracy of our approach. We investigate the stability of these materials under simulated experimental conditions, considering both the rich and poor chemical potentials of their precursor salts. Our results indicate distinct regions of surface energy stability that favor CsX terminations. In contrast, MX$_4$ terminations show in-gap surface states, which can act as trap states and reduce carrier lifetime. Finally, based solely on the intrinsic absolute energy levels, we identify promising candidates as charge transport and injection layers for typical photovoltaic and light-emitting applications. This study provides a detailed map of energy level alignment at Cs$_2$MX$_6$ surfaces, offering valuable design principles for the development of next-generation Cs$_2$MX$_6$-based optoelectronic devices.
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Materials Science · Cross-listed from quant-ph

Oxide-Nitride Heteroepitaxy for Low-Loss Dielectrics in Superconducting Quantum Circuits

David A. Garcia-Wetten, Mitchell J. Walker, Peter G. Lim et al. (+9 more)

Superconducting qubits show great promise for the realization of fault-tolerant quantum computing, but lossy, amorphous dielectrics limit current technology. Identifying highly crystalline and stoichiometric dielectrics with intrinsically low microwave loss is therefore a central materials challenge, yet experimentally validated platforms remain scarce. This work integrates a crystalline dielectric into a heteroepitaxial TiN/$\gamma$-Al$_2$O$_3$/TiN trilayer grown via pulsed laser deposition. Correlative high-resolution imaging, diffraction, and spectroscopy measurements confirm the single-crystal quality and chemical integrity of all layers, with minimal defects and limited anion interdiffusion across the oxide-nitride interfaces. Using microwave lumped-element resonators with parallel-plate capacitors, this work establishes an experimentally-measured upper bound for the dielectric loss of $\gamma$-Al$_2$O$_3$, which has a low intrinsic two-level system loss of $\delta_{\text{TLS}}^0 = (2.8 \pm 0.1) \times 10^{-5}$. These results establish heteroepitaxial oxides on transition metal nitrides as an attractive materials platform for superconducting quantum circuits, particularly for integration into compact device architectures such as merged-element transmons and microwave kinetic inductance detectors.
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All authors David A. Garcia-Wetten, Mitchell J. Walker, Peter G. Lim, André Vallières, Maria G. Jimenez-Guillermo, Miguel A. Alvarado, Dominic P. Goronzy, Anna Grassellino, Jens Koch, Vinayak P. Dravid, Mark C. Hersam, Michael J. Bedzyk

Statistical Mechanics

Longest weakly increasing subsequences of discrete random walks on the integers with heavy tailed distribution of increments

José Ricardo G. Mendonça and Marcelo V. Freire

We investigate the behavior of the length of the longest weakly increasing subsequences (weak LIS) of $n$-step random walks with nonzero integer increments $k = \pm 1, \pm 2, \dots$ given by a symmetric heavy tailed mass distribution proportional to $|k|^{-1-\alpha}$ for several values of the real parameter $\alpha > 0$ together with that of the simple random walk ($k=\pm 1$), to which the $n$-step heavy tailed walks reduce when $\alpha$ grows large enough that step jumps beyond $\pm 1$ become essentially absent on the scale of $n$. By means of exploratory fits, weighted nonlinear least squares, and nested-model comparisons, we found that the sample average length $\langle{L_{n}}\rangle$ scales like $\langle{L_{n}}\rangle \sim \sqrt{n}\log{n}$ when the distribution of increments has finite variance ($\alpha > 2$) and $\langle{L_{n}}\rangle \sim n^{\theta}$ with a varying exponent $\theta > 0.5$ when the variance is infinite ($\alpha \leq 2$). Distributional diagnostics indicate that the bulk of the $L_{n}$ distribution is very well-approximated by a lognormal model, though systematic deviations are observed in the tails. Our results corroborate and expand upon previous results for the LIS of other types of heavy-tailed random walks and raise a conjecture as to whether the distribution of $L_{n}$ is given, or can be effectively described, by a lognormal distribution.
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Materials Science

Singing Materials: Initial experiments in applying sonification to phonon spectra

Lucy Whalley, Rose Shepherd, Jorge Boehringer et al. (+8 more)

Solid materials may appear static, but at the atomic scale they are in constant vibrational motion. These vibrations, described by phonons, govern many key material properties, including structural stability, mechanical strength, optical behaviour, and thermal transport. Understanding phonon physics is therefore central to the rational design of materials with targeted functionalities. Singing Materials is a research project that explores how sonification can be applied to this domain. In this work, we introduce `SingingMaterials`, a modular Python package for sonifying materials simulation data. The software interfaces with the Materials Project database and is designed to be extensible, enabling the incorporation of additional sonification strategies and data sources. Built using the Sonification Toolkit `STRAUSS`, the current implementation supports three core approaches: spectral, synthesised, and sample-based. We demonstrate these approaches using phonon density-of-states data and evaluate their effectiveness through a user study, investigating whether listeners can distinguish differences in material properties from their auditory representations. The results show that sonification can provide an interpretable and complementary approach for exploring vibrational materials data.
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All authors Lucy Whalley, Rose Shepherd, Jorge Boehringer, Shelly Knotts, Paul Vickers, George Caselton, Carol Davenport, Christopher Harrison, Bennett Hogg, Antonio Portas, Daniel Ratliff

Statistical Mechanics

Non-Hermitian Causal Memory Generates Observable Temporal Correlations Invisible to Spectral Analysis

Mario J. Pinheiro

We identify a new class of non-Hermitian causal processes that produce statistically significant temporal correlations invisible to conventional spectral methods. Using a generative model with a strictly causal memory kernel, we demonstrate that time-asymmetric stochastic processes naturally yield sharp transitions at characteristic scales that appear as localized structures in similarity space but leave no trace in power spectra. The model predicts an asymmetric transition profile with orientation-dependent asymmetry parameter $A(\theta)=A_0\cos(\theta+\delta)$ and achieves quantitative agreement ($\chi^2/\mathrm{dof}=0.50$, $p=0.86$) with high-precision counting experiments exhibiting $p<10^{-15}$ significance. These results establish a fundamental limitation of spectral analysis for non-Hermitian, non-stationary processes and provide experimentally testable signatures of causal memory in open quantum systems.
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