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Physics Condensed Matter

cond-mat Watch Condensed Matter

Monday 25 May

Quantum Gases

Response of a dipolar BEC to Laguerre-Gaussian beam driven STIRAP

Deepu Singh, Hari Sadhan Ghosh, Arpana Saboo et al. (+2 more)

Coherent light-matter coupling via STIRAP can offer a versatile route to nucleate quantized vortices in Bose-Einstein condensates through the orbital angular momentum transfer from a vortex beam, yet its efficacy in dipolar condensates remains an open question. Can the orbital angular momentum of a Laguerre-Gaussian beam be coherently transferred to a dipolar BEC via STIRAP? We investigate this for a quasi-two-dimensional trapped dipolar condensate using co-propagating Gaussian and Laguerre-Gaussian laser beams. The interplay between long-range dipole-dipole interactions and short-range contact interactions enables access to three interaction-driven phases: superfluid, droplet, and supersolid. We find that the amount of angular momentum transferred from the optical field to the dipolar condensate, along with the nucleation and persistence of vortices, depends strongly on the underlying phases of the dipolar BEC. In the superfluid, STIRAP achieves a near-complete population transfer and nucleates a long-lived quantized vortex, reflecting efficient transfer of angular momentum to the condensate. In the droplet phase, although the vortex remains pinned within the density profile, the angular momentum is partially retained and oscillatory, accompanied by droplet fragmentation and recombination. In the supersolid phase, when the external magnetic field is oriented perpendicular to the LG beam's propagation direction, the emergence of a modulated density distribution along with a slight reduction in inter-droplet coherence leads to vortex delocalization and eventually exits from the condensate along the field direction, yielding a vanishing average angular momentum. However, reorienting the magnetic polarization along the beam propagation direction restores efficient angular momentum transfer and stabilizes the vortex within the supersolid phase.
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All authors Deepu Singh, Hari Sadhan Ghosh, Arpana Saboo, Soumyadeep Halder, Sonjoy Majumder

Soft Condensed Matter

Characterizing emergent multiscale dynamics in colloidal nanoparticle gels

William D. Brackett, Zachary M. Sherman, Felix Lehmkühler et al. (+2 more)

Colloidal gels assembled from nanoparticles (NPs) are a versatile class of soft network-based materials capable of rich dynamic, mechanical, and even optical or magnetic responses to stimuli. Understanding how their hierarchically organized processes relate to macroscopic network properties remains a broad and unresolved problem in soft matter physics. The mechanisms of gel formation can depend sensitively on the pathway and the nature of NP interactions, thus far preventing a unified theoretical bridge between nanoscopic interactions and structural evolution and network dynamics. Indirect measurement of dynamics using light-scattering techniques provides an experimental means to quantify underlying particle and network motion. X-ray photon correlation spectroscopy (XPCS) has emerged as a powerful tool for probing nanoscopic motion in nanoparticle gels, but alone cannot resolve the full spatiotemporal spectrum of dynamics that drive gelation, aging, and network mechanical properties. While in situ rheo-XPCS enables simultaneous probing of nanoscale and bulk mechanical responses, complementary light scattering, microscopy, or simulations can extend spatiotemporal characterization and, consequently, understanding of NP gel network physics. Implementing a modular model platform with tunable primary nanoparticle features allows systematic variation of nanoscopic characteristics that drive emergent gel responses and inform the development of theoretical models for a wide range of soft, dynamic, nanostructured materials. The rapid expansion of XPCS capabilities at fourth-generation light sources, combined with complementary tools and robust model systems, positions the field to move beyond descriptive fundamental studies toward the design of nanoparticle gels with adaptive and programmable behaviors.
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All authors William D. Brackett, Zachary M. Sherman, Felix Lehmkühler, Thomas M. Truskett, Delia J. Milliron

Mesoscale and Nanoscale Physics

Observation of the Optical Phonons in {\alpha}-MnTe films

Himanshu Sheokand, Arun K Kumay, Mazharul Islam Mondal et al. (+6 more)

The altermagnetic materials have emerged as model systems for studying spin split electronic structures, yet controlled epitaxial growth on technologically relevant substrates remains challenging. Among the known candidates, MnTe stands out as a prominent altermagnetic material owing to its layered structure and high Neel temperature. Here, we report the molecular beam epitaxy (MBE) growth of high quality alpha MnTe thin films on GaAs(111)B substrates and provide a comprehensive analysis of the growth evolution and structural properties. Raman spectroscopy reveals multiple vibrational features of alpha MnTe including modes near 121, and 140 1/cm. Combined with first principles phonon calculations, these features are identified as the Raman-active phonons of the hexagonal NiAs type lattice. Our results show that the high crystalline quality of MBE grown alpha MnTe enables the complete experimental resolution of all symmetry allowed Raman active phonon modes, highlighting epitaxial alpha MnTe as a robust thin film platform for investigating altermagnetism and its lattice coupled excitations.
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All authors Himanshu Sheokand, Arun K Kumay, Mazharul Islam Mondal, Milo Sprague, Ravinder Sharma, Jayan Thomas, Dariusz Kaczorowski, Andrzej Ptok, Madhab Neupane

Materials Science

Magneto-optic phonon resonances in magnetic topological EuCd2As2 via helical Raman spectroscopy

Jin Ho Kang, Liangbo Liang, Ioannis Petrides et al. (+6 more)

EuCd2As2 materials have two magnetic ordering states: antiferromagnetic (AFM) and ferromagnetic (FM) when their chemical tunability is utilized. While AFM-EuCd2As2 has a nonzero magnetoelectric response due to its symmetry breaking with spin configuration, FM-EuCd2As2 is an ideal candidate for studies of Weyl physics because of its minimum number of Weyl points with opposite chirality. In this article, we examine cryogenic low-frequency Raman spectroscopy of phonon modes in FM-EuCd2As2 crystals using circular polarization configurations, with support from density functional theory calculations, and investigate in-plane magneto-anisotropy by linear polarization configuration below the Curie temperature (Tc = 26 K). We attribute the anomalous enhancements in Raman intensities below the Curie temperature are due to spin-phonon coupling. Furthermore, we see that A-mode peaks can be distinguished by magneto-helical Raman spectroscopy through the magneto-optic effect and that the degree of circular polarization (DCP) of 12.5 meV peak reaches 60% at 4.2 K and becomes saturated. We also examine AFM-EuCd2As2 below Néel temperature (TN = 9 K) to compare with FM-EuCd2As2, but we hardly observe spin-phonon coupling and find negligible DCP values due to almost zero net magnetization. Our results contribute to the understanding of the phonon dynamics and the interplay between topology and magnetism in FM-EuCd2As2, through helical light and external magnetic fields. This lays the foundation for utilizing state-of-the-art Weyl systems for applications in thermoelectrics, phononic devices, and topological quantum computing.
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All authors Jin Ho Kang, Liangbo Liang, Ioannis Petrides, Subhajit Roychowdhury, Kai-Chi Chang, Chandra Shekhar, Claudia Felser, Prineha Narang, Chee Wei Wong

Materials Science

Theory of Electrically Detected Magnetic Resonance of Silicon Vacancy-Related Spin Pairs in Silicon Carbide

David A. Fehr, Corey J. Cochrane, Stephen R. McMillan et al. (+3 more)

We present a quantitative theory for simulating the electrically detected magnetic resonance (EDMR) of silicon vacancy-related spin pairs in silicon carbide using steady-state Lindblad master equations. In our theory, we consider V1a and V2a deep level silicon vacancies near the (0/-) charge state transition level in proximity to a previously identified nitrogen-related complex, the incomplete K-center, due to the hyperfine, spin structure, and Landé g factor of the shallow state. Our theory describes recent room temperature measurements attributed to V1a silicon vacancies, with reasonable extracted parameters for defect spin coherence times and electrical transport rates. At lower temperatures we predict that the shallow level hyperfine structure may be spectrally resolvable. Finally, we predict the EDMR spectrum of V2a silicon vacancy-related spin pairs and predict that two-photon, double quantum transitions of the silicon vacancy's negative charge state can be electrically read-out for enhanced magnetic field sensing.
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All authors David A. Fehr, Corey J. Cochrane, Stephen R. McMillan, Nicholas J. Harmon, Patrick M. Lenahan, Michael E. Flatté

Statistical Mechanics

Effect of slow bonds on current fluctuations in the symmetric simple exclusion process

Soumyabrata Saha, Sandeep Jangid, Kapil Sharma et al. (+1 more)

The symmetric simple exclusion process (SSEP) is a paradigmatic model of classical non-equilibrium dynamics. Exact results for large deviations of particle current in the SSEP have been obtained in various settings using integrability-based methods. In this Article, we discuss how these results are modified in the presence of localized slow bonds. We consider three conventional geometries: (a) a finite one-dimensional lattice weakly coupled to unequal reservoirs at its boundaries, (b) a semi-infinite one-dimensional lattice weakly coupled to a boundary reservoir, and (c) an infinite one-dimensional lattice with localized slow bonds near the origin. For each case, we present exact expressions for the large deviation function of current and validate them through rare-event simulations based on the cloning algorithm. In connection with our results, we present an elementary derivation of the exact large deviation function for the current in the semi-infinite SSEP, complementing recent results obtained through more elaborate techniques.
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All authors Soumyabrata Saha, Sandeep Jangid, Kapil Sharma, Tridib Sadhu

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Absolute measurement of the intrinsic helicity in nanophotonics

Malo Bézard, Simon Garrigou, Jérémie Béal et al. (+5 more)

Helicity is a universal quantity describing the internal rotation of an object or a field. Whether it characterizes fundamental properties such as the spin of elementary particles or leads to practical consequences such as the toxicity or harmlessness of chiral molecules, defining and measuring it is essential. However, this remains ambiguous in the case of chiral photonic systems such as plasmonic nanoparticles or photonic metasurfaces, where contrary to common knowledge, the observation of circularly polarized dependent optical properties is not a relevant measure for the helicity. We demonstrate experimentally and theoretically that the helicity can be rigorously defined and measured in a nanophotonic system emitting circularly polarized light after excitation in the near-field by a focused electron beam. In the case of a model system composed of two plasmonic dipoles (Born-Kuhn systems), we show that the helicity of photonic modes takes on a very intuitive form and can be simply measured by symmetrizing the geometry of excitation and detection. The method could be extended to a variety of chiral photonic systems, whose locally enhanced properties make them promising for the engineering of local chirality.
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All authors Malo Bézard, Simon Garrigou, Jérémie Béal, Andreas Horrer, Yves Auad, Hugo Lourenço-Martins, Davy Gérard, Mathieu Kociak

Materials Science

Nuclear-Electron Hyperfine Coupling of the Shallow States Associated with Vacancies in Gallium Nitride

Joseph Sink and Michael E. Flatté

We use multiband real space Green's functions computed using open-boundary conditions for clean GaN to exactly solve the potential-scattering Dyson equation to obtain the electronic structure of single nitrogen and gallium vacancies. From these vacancy solutions, we compute the local density of states as well as the Fermi contact and anisotropic contributions to the hyperfine field in the vicinity of the defect. These quantities directly affect electrically-detected magnetic resonance signals, which can be used to identify these defects when present in GaN devices.
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Strongly Correlated Electrons

Magnetic ground state of a prototype quasicrystal approximant: a candidate for octahedral spin ice physics

Leonie Woodland, Farid Labib, Dmitry Khalyavin et al. (+4 more)

Magnetic ordering in quasicrystals has recently emerged as a fertile ground for discovering unconventional magnetic states beyond the framework of periodic crystals. However, elucidating the microscopic origin of such states remains challenging due to the intrinsic aperiodicity of quasicrystals. Here, we address this issue by investigating the prototypical Tsai-type quasicrystal approximant Cd6Tb, which preserves the essential local geometry and connectivity of icosahedral quasicrystals while allowing detailed structural and magnetic characterization due to its translational periodicity. Using neutron diffraction measurements, we find a noncoplanar multi-k magnetic ground state composed of Ising-like Tb moments arranged on a network of corner-sharing octahedra, the ingredients required to host octahedral spin-ice physics. Remarkably, only one third of the Tb moments develop long-range magnetic order, whereas the remaining moments display strongly reduced static order accompanied by persistent spin dynamics on microsecond timescales, as evidenced by muon spin rotation. This coexistence of ordered and fluctuating moments constitutes a potential realization of magnetic fragmentation - a key prediction of octahedral spin-ice physics - in a quasicrystal-related material.
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All authors Leonie Woodland, Farid Labib, Dmitry Khalyavin, Pascal Manuel, Fabio Orlandi, Hubertus Luetkens, Ryuji Tamura

Statistical Mechanics · Cross-listed from cs.CV

Everything at Every Scale: Scale-Invariant Diffusion with Continuous Super-Resolution

Zixin Jessie Chen, Zhuo Chen, Archer Wang et al. (+4 more)

Creating images from noise is image generation; reconstructing fine details from coarse inputs is super-resolution. Despite their practical differences, both can be understood as reversing information loss across scales. We introduce $\textbf{SKILD}$, a $\textbf{S}$cale-invariant $\textbf{K}$-Space $\textbf{I}$mage $\textbf{L}$earning $\textbf{D}$iffusion model that unifies generation and continuous super-resolution within a single unconditional framework. Both natural images and critical physical systems exhibit scale invariance, and we leverage it to design a forward process that attenuates image content from fine to coarse scales while injecting spectrum-matched Gaussian noise, making scale an explicit coordinate of the diffusion dynamics. The same trained reverse process performs generation and continuous super-resolution by varying only the starting timestep: $\textit{no task-specific architecture, no conditioning branch, no classifier-free guidance, no retraining per scale factor}$. Empirically, SKILD reaches FID $2.65$ and Inception Score $9.63$ on unconditional CIFAR-10, performs $2\times$–$8\times$ super-resolution on ImageNet from a single unconditional checkpoint while outperforming conditional models across perceptual metrics, and reconstructs critical Ising models whose connected four-point correlations closely track the ground truth.
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All authors Zixin Jessie Chen, Zhuo Chen, Archer Wang, Jeff Gore, William T. Freeman, Congyue Deng, Marin Soljačić

Soft Condensed Matter

Liquid-Liquid Phase Separation in a Minimal Explicit-Solvent Lattice Model Mimicking Protein Solutions

Siddhartha Roy and Rakesh S. Singh

Biomolecular condensates play essential roles in cellular processes, and recent efforts have focused on understanding their assembly and rational design principles. In this study, we have employed an explicit-solvent minimal statistical mechanical model based on the lattice-gas Hamiltonian with quenched disorder – which mimics crowders – to investigate how protein-solvent and protein-crowder interactions influence condensate phase behavior and morphology. The computed phase diagrams reveal rich behavior, including upper critical solution temperature (UCST), closed-loop, and reentrant type transitions under varying protein-solvent interactions at both equilibrium and out-of-equilibrium conditions. We elucidated the origin of these phase behavior changes and examined the role of protein-crowder interactions in modulating condensed phase morphology and stability. We further extended this model to binary protein mixtures where we studied the phase behavior in the presence and absence of quenched disorder. Without disorder, the system exhibits diverse phase-separated morphologies – partially wetted, fully wetted, segregative, and associative – with phase boundaries delicately sensitive protein-solvent interactions. The introduction of quenched disorder (or crowder) leads to a broader spectrum of complex morphologies, dictated by the interplay among protein-protein, protein-solvent, and protein-crowder interaction parameters. In general, this work underscores that protein-solvent and protein-crowder interactions, together with protein-protein interactions, can act as key regulatory parameters for modulating condensate morphology. These insights may guide future computational and experimental studies of liquid-liquid phase separation in biomolecular systems aimed at designing stimuli-responsive condensates.
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Materials Science · Cross-listed from physics.comp-ph

Uncovering multi-channel magnetic hopfion annihilation via a single-node, billion-spin-scale atomistic framework

Qichen Xu and Anna Delin

Modern atomistic spin simulations combine long stochastic trajectories, thermodynamic sampling, static optimization and multi-image transition-path workflows, all of which rely on repeated evaluation of spin Hamiltonians and become computationally prohibitive on the large lattices required for three-dimensional magnetic textures. We introduce SpinX, a GPU-native atomistic spin simulation framework built around a unified Hamiltonian interface and multiple user-selectable computational backends. Its core is a crystallographic sublattice decomposition that reformulates translationally invariant spin interactions as multi-channel tensor convolutions, enabling dense, sparse and FFT-based convolution backends, while irregular systems are handled by pair-list evaluation and long-range dipolar fields by reciprocal-space FFT. Implemented in JAX, SpinX supports deterministic and stochastic Landau-Lifshitz-Gilbert dynamics, Monte Carlo sampling, static optimization, dynamical spectroscopy and string and geodesic nudged elastic band transition-path calculations on heterogeneous accelerator platforms. A validated mixed-precision mode combines fp32 field evaluation with fp64 spin-state propagation. We validate SpinX against analytical single-spin dynamics, finite-size thermodynamics of bcc Fe and transverse dynamic structure factors. Performance benchmarks show peak throughput exceeding 10 billion spin-site operations per second on a single accelerator and aggregate single-node workloads of over 1 billion atomic spins. Applying this framework to an exchange-stabilized magnetic hopfion, we uncover two competing annihilation channels on a million-spin atomistic lattice: a previously reported axial-collapse pathway and a distinct lateral-rupture pathway with a different transition morphology and activation barrier.(Due to arXiv's limit, the abstract shown here is a shortened version)
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Soft Condensed Matter

Topology of pulsating active matter: Defect asymmetry controls emergent motility

Luca Casagrande, Alessandro Manacorda and Étienne Fodor

In pulsating active matter, topological defects are motile despite the absence of any macroscopic flows and microscopic self-propulsion. We reveal that this motility arises from a ratchet effect: the mechanochemical coupling between local oscillations and repulsive interactions breaks both spatial and time-reversal symmetries, thus leading asymmetric rotating defects to drift under fluctuations. This mechanism regulates a crossover between spiral waves connecting slow defects and fiber-like waves connecting fast defects, in analogy with the onset of heart rhythm disorder in cardiac tissues. We rationalize this crossover in terms of a fluctuating hydrodynamics that captures how motile defects spontaneously nucleate and move within an ordered background.
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Strongly Correlated Electrons

Demagnetization effect on magnetic noise measurements in spin ice materials

F. Morineau, C. Paulsen, G. Balakrishnan et al. (+4 more)

Magnetic noise spectroscopy provides direct access to spontaneous time-dependent magnetization fluctuations in correlated magnetic systems, including spin liquids, spin ices, and spin glasses. Here we investigate how demagnetizing fields shape the magnetic noise spectra measured in spin ice. By combining magnetic noise and ac susceptibility measurements on single-crystal spin ice samples with different sizes and shapes, we show that magnetic noise, like linear response, is strongly renormalized by sample geometry. As a consequence, measured noise spectra do not directly yield the intrinsic fluctuation spectrum, and demagnetization corrections cannot in general be determined from noise data alone. Instead, sample geometry must be treated as a central experimental control parameter for accessing intrinsic dynamics. These results establish the role of boundary conditions in fluctuation spectroscopy and provide a framework for quantitatively comparing noise measurements with microscopic theories of spin dynamics.
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All authors F. Morineau, C. Paulsen, G. Balakrishnan, D. Prabhakaran, K. Matsuhira, S. R. Giblin, E. Lhotel

Soft Condensed Matter

Beyond Gaussian Statistics in Polymer Melts: Statistical Masking of Persistent Local Constraints

José A. Martins

Short polymer chains exhibit clear deviations from Gaussian end-to-end distance statistics, yet the molecular mechanism by which Gaussian behavior is recovered in long chains remains unestablished. Atomistic molecular dynamics simulations of polyethylene melts reveal that conformational heterogeneity persists at the Kuhn scale across all chain lengths, consisting of a mosaic of slow-relaxing, extended aligned chain segments (ACS) and coiled segments – random conformational sequences (RCS) and chain ends (CE). We show that the end-to-end distance distributions for both unentangled and entangled chains are accurately described by a $q$-Gaussian function, with the entropic index $q$ increasing systematically from $0.67$ (C50) to $0.99$ (C500). This evolution tracks the emergence and accumulation of RCS segments, which are absent in short chains, establishing $q$ as a quantitative “heterogeneity index”. The $q < 1$ values are a signature of non-extensive statistics, with the ratio of Tsallis to Boltzmann-Gibbs entropy ($S_q/S_1$), computed directly from simulation data without fitting, decreasing from $1.80$ (C50) to $1.03$ (C500). Crucially, we demonstrate that Gaussian recovery does not result from the erasure of Kuhn-scale heterogeneities, as ACS domains persist in all chain lengths above the critical mass ($\approx 35\%$). Instead, the transition to Gaussian statistics is a statistical masking effect, where the accumulation of independent RCS segments progressively obscures the non-Gaussian signatures of the persistent ACS domains.
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Statistical Mechanics

Boltzmann Distribution from Invariance of Coarse-Graining-Scale and Energy-Shift

Weicheng Fu, Yisen Wang, Yong Zhang et al. (+1 more)

We present a concise derivation of the Boltzmann form for single-particle energy distributions in classical many-body Hamiltonian systems. The derivation relies on two physical facts: coarse-graining-scale invariance of the empirical distribution and invariance under a uniform shift of the energy zero. These conditions uniquely yield the Boltzmann factor, whose parameter is fixed by the mean energy per particle. For separable Hamiltonians, the equilibrium weight factorizes into kinetic and configurational contributions sharing the same parameter, identified from the kinetic part as the inverse kinetic temperature. The principle extends to any physical quantity with a stationary distribution and translational invariance. It is illustrated in a one-dimensional diatomic hard-core gas and a nonlinear lattice chain, where it predicts velocity, energy, spacing, collision-time, and pressure-dependent displacement distributions in agreement with simulations. The lattice model further shows how harmonic elasticity, anharmonic corrections, internal pressure, and thermal expansion emerge from the same exponential equilibrium weights. Finally, the relationships among different ensembles are briefly discussed.
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All authors Weicheng Fu, Yisen Wang, Yong Zhang, Hong Zhao

Materials Science

Light-Induced Transient Polarization Reversal in Rhombohedrally Stacked Bilayer Transition Metal Dichalcogenides via an Electronic Mechanism

Xiangzhou Zhu, Stefano Mocatti and Matteo Calandra

Light-induced sliding ferroelectricity in two-dimensional van der Waals materials enables polarization control via relative layer motion. However, polarization switching occurs on the time scale of shear modes (tens of ps) and requires very large fluences, potentially damaging the samples. Here, using constrained density functional theory and many-body real-time simulations, we demonstrate an ultrafast electronic reversal of the total out-of-plane polarization sign in the photoexcited state, without requiring interlayer sliding, in rhombohedrally stacked transition-metal dichalcogenide bilayers. The polarization changes sign relative to its initial ground-state value at moderate fluences and within $\sim$ 200 fs, about 50 times faster than the typical shear-mode period. The ultrafast switching is driven by a rearrangement of localized dipoles around the tungsten sites. We establish a novel general mechanism for electronic control of low-dimensional ferroelectrics common to all polar multilayers having type II band alignment. Our work has direct implications for ultrahigh-speed volatile optical memory operating on sub-ps time scales.
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Soft Condensed Matter

Excess entropy scaling of the transverse sound speed in simple fluids

Sergey Khrapak

A calculation of the transverse sound velocity as a function of excess entropy is presented for several simple fluids, including the Lennard-Jones, Yukawa, one-component plasma, inverse-power law (soft sphere) and hard sphere models. A quasi-universal character of this dependence is established, extending Rosenfeld's excess-entropy scaling of transport coefficients to the transverse sound velocity. The results are discussed in terms of the soft- to hard-sphere crossover and the Frenkel crossover between gas-like and liquid-like dynamics.
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Strongly Correlated Electrons

Trimerized Spin-$1/2$ Chain: Emergent Low-Energy Hamiltonian, Higher-Energy Excitations, and Magnetic and Thermodynamic Responses

Snehasish Sen and Sudhansu S. Mandal

We investigate a spin-1/2 antiferromagnetic chain with trimerized exchange couplings relevant to Na$_2$Cu$_3$Ge$_4$O$_{12}$. We show that the low-energy Hilbert space maps onto an effective Heisenberg chain of composite spin-1/2 trimer degrees of freedom with positive coupling, enabling an exact spinon excitations via the Bethe ansatz. To access higher-energy dynamics, we develop a self-consistent Jordan-Wigner mean-field theory that yields three fermionic bands reflecting the underlying trimer structure. Remarkably, this approach reproduces the exact low-energy spinon continuum while predicting two additional higher-energy excitation bands consistent with the experimental observations and previous numerical simulations. The theory further captures the 1/3 magnetization plateau under an applied magnetic field, and provides testable predictions in magnetic susceptibility and specific heat. Our results establish a unified framework connecting low- and high-energy excitations in trimerized quantum spin chains.
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Materials Science

Berry Curvature Driven Transport in Silicon-Compatible Altermagnetic $\alpha$-MnTe Thin Films

Rajib Sarkar, Subhransu Kumar Negi, Arindom Das et al. (+10 more)

Integrating spin-dependent functionality with mainstream semiconductor technology is a central goal of modern spintronics, yet most candidate materials remain incompatible with silicon-based platforms. Here, we report the direct epitaxial integration of $\alpha$-MnTe thin films on Si(111) via molecular beam epitaxy and demonstrate a robust anomalous Hall effect (AHE) in this silicon-compatible altermagnetic system. Despite the absence of net bulk magnetization, the films exhibit a pronounced hysteretic Hall response, providing transport evidence consistent with finite Berry curvature generated by symmetry breaking in the thin-film geometry. High-resolution structural and spectroscopic characterization confirms phase-pure, epitaxial growth with hexagonal NiAs-type symmetry, while magnetotransport measurements reveal correlated hysteresis in both transverse and longitudinal channels with systematic temperature evolution. First-principles calculations reveal substantial uncompensated Berry curvature arising from the spin-split band structure, consistent with altermagnetic symmetry and the origin of the observed Hall response. These results establish MnTe/Si(111) as a silicon-compatible altermagnetic platform and chart a concrete pathway for embedding Berry-phase-driven functionalities into scalable semiconductor device architectures.
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All authors Rajib Sarkar, Subhransu Kumar Negi, Arindom Das, Arijit Mandal, Pankaj Bhardwaj, Sohini Guin, Aryaman Das, Naresh Shyaga, Kartick Biswas, Pavan Nukala, Laxmipriya Nanda, B. R. K. Nanda, Dhavala Suri

Statistical Mechanics

Relevant–marginal field mixing resolves the four-state Potts endpoint in the square-lattice $J_1$–$J_2$ Ising model

Yihua Sun and Yuchen Fan

Identifying endpoint criticality is challenging because pseudo-first-order signatures can persist over accessible system sizes and obscure the underlying scaling behavior. This difficulty is especially acute in the frustrated square-lattice \(J_1\)–\(J_2\) Ising model, where the location and even the nature of the stripe-ordering endpoint have remained controversial for decades. Here we treat this endpoint as a relevant–marginal two-field scaling problem and develop a generalized field-mixing construction to resolve the endpoint ambiguity. Mixed-histogram symmetry defines a finite-size pseudotransition manifold, transforming pseudo-first-order finite-size structure into a scaling trajectory on which the normal relevant detuning is removed and the residual marginal drift is exposed. Along this manifold, Binder analysis locates the endpoint as a distinct singular point, while mixed-histogram scaling, comparison with the Ashkin–Teller Potts point, and complementary Binder scaling establish four-state Potts endpoint criticality with logarithmic corrections.
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Superconductivity

Exact Single-Scale Outer Solution of the Abrikosov Vortex in the Extreme Type-II Limit

Eugene B. Kolomeisky

We determine the exact outer structure of the Abrikosov vortex in the extreme type-II limit, which occurs when the Ginzburg-Landau parameter $\kappa$ diverges. In this limit, Ginzburg-Landau theory simplifies, outside a shrinking core, to a closed nonlinear theory for the superfluid velocity subject to an algebraic density constraint. The resulting solution is asymptotically exact everywhere outside the vanishing vortex core, demonstrating that both magnetic field and superconducting density vary on the length scale of the London penetration depth. This establishes that the conventional two-length-scale picture of the vortex does not hold in the $\kappa\gg 1$ limit.
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Statistical Mechanics

Freezing of the tetrahedral amorphous network in supercooled water triggers crystallization towards LDA ice

Ashutosh Srivastava and Pankaj A. Apte

In this work, we provide mechanistic insight into the initial stages of formation of ice across the limit of stability of supercooled water. Such an analysis is particularly important since crystal nucleation is not a relevant mechanism under these conditions. Using molecular dynamics simulation with the TIP4P/2005 potential, water is cooled at a constant pressure with cooling rates of 5 to 10 K per nanosecond. As the liquid is cooled across the temperature of maximum density (T_0 = 277 K), we find that there is a continuous increase in the tetrahedrality of the system. As the cooling continues across the limit of stability of water (T_s $\approx$ 235 K), large scale thermal fluctuations dissipate while the thermal equilibration is achieved through small scale fluctuations. This phenomenon, known as the dynamical crossover [Goutam et. al. in J. Stat. Phys., 168: 1302–1318 (2017)], ends the existence of the liquid state. Subsequently, we find that the tetrahedral network drives the decrease of energy and density. This process terminates when the network undergoes `freezing' (i.e., the bonds of the network acquire sufficient rigidity), due to which the network evolution, as a whole, stops. This triggers a qualitative change in the relaxation mechanism: subsequent relaxation occurs through crystallization, i.e., an increase in the structural order. In particular, we find that the cubic and hexagonal crystalline motifs, which possess medium range order, increase rapidly across the freezing point. In the resulting LDA ice states, cubic ice is found to have a significant contribution in the overall extent of crystallization, which is consistent with the experimental findings. Overall, our work provides the specific mechanism by which crystallization (leading to LDA ice) is initiated across the limit of stability of supercooled water.
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Other Condensed Matter

Mutual Friction in Dissipative Gross-Pitaevskii Thermal Counterflow Turbulence

Kyo Yoshida, Hideaki Miura and Yoshiyuki Tsuji

We report numerical simulations of the dissipative Gross-Pitaevskii equation for a bulk region of thermal-counterflow turbulence. Quasistationary states are obtained over a range of forcing, damping, and healing-length parameters. The mutual-friction acceleration exhibits cubic scaling with the mean relative velocity between the superfluid and normal-fluid components, and the coefficient of this scaling is linked to the phenomenological damping parameter. The intervortex spacing follows the expected dimensional scaling in the weak-forcing regime. Comparison with a straight-vortex-line model suggests that the vortex-line orientations are nearly isotropic.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Native topological readout on qubit hardware: a Fibonacci-chain benchmark of measurement-compilation trade-offs

Babatunde Moses Ayeni

Recent demonstrations of non-Abelian braiding of graph vertices on noisy intermediate-scale quantum (NISQ) superconducting processor, and the experimental realization of topological order in general on various quantum hardware platforms necessitate an important question: when does a native (topological) fusion readout genuinely help for topological anyonic Hamiltonians implemented on NISQ hardware? We use the Fibonacci anyons chain as a concrete model for understanding the trade-off between measurement cost and compilation cost in that setting. The comparison is made against a simple grouped-Pauli baseline, and is scored by a covariance-aware mean-squared-error (MSE) of the full energy estimator. We based our benchmark on two different important classes of quantum circuits, namely Floquet time-evolved and variational quantum eigensolver quantum circuits, with the underlying Hamiltonian consisting of both braiding and fusion interaction. Our analysis found that there is not a uniform best method across both problems: the fusion readout method performed better on Floquet-type circuits on both the MSE and covariance-aware sampling variance, while the grouped Pauli method performed better on VQE on the MSE but worse on sampling variance. We derive scaling laws, and compute shot-budget crossover points, where one method is operationally favored above the other. The relevance of this work extends beyond Fibonacci chains to two-dimensional topological models compiled on superconducting and other qubit-native platforms, and can be used as a guide in answering the question of when one should measure in the native operator basis of the target physics, or when it is better to fall back on Pauli-basis reconstruction.
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Superconductivity

Substitution modulated transition from semimetal to superconductor in ZrTe$_{2-x}$Se$_x$ with coexistence of nontrivial electronic topology

V. M. Fim, C. F. Schuch, L. R. de Faria et al. (+5 more)

This study explores the emergence of superconductivity in high-quality ZrTe$_{2-x}$Se$_x$ crystals, grown via the isothermal chemical vapor transport (ICVT) technique. Resistive, structural, and thermal measurements reveal that substituting Te with Se in the ZrTe$_2$ matrix induces a superconducting state at low temperatures. The critical temperature ($T_c$) exhibits a clear dependence on the selenium concentration, peaking at $x=0.15$ with a $T_c$ of $4.8$ K. Calorimetric data indicates that even a low Se substitution range is capable of modifying both the electronic contribution and the vibrational modes of the crystal lattice. Combined with ab initio calculations and Wannier Hamiltonian interpolation between ZrTe$_2$/ZrSe$_2$, we established an extensive phase diagram mapping the transition from charge density wave (CDW) to the state with coexistence between the Dirac semimetal and superconductivity (SC), up to the semiconductor phase. This coexistence suggests that ZrTe$_{1.85}$Se$_{0.15}$ could be a candidate platform for topological superconductivity, as it hosts a nontrivial $\mathbb Z_2$ invariant, with nonvanishing surface states in its $(001)$ planes.
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All authors V. M. Fim, C. F. Schuch, L. R. de Faria, F. A. Santos, M. S. da Luz, S. S. Tsirkin, L. T. F. Eleno, A. J. S. Machado

Materials Science

Benchmarking Transparent Conductors

Amit Cohen and Lior Kornblum

Transparent conducting oxides (TCOs) are central to optoelectronic technologies, yet their design is often guided by popular figures of merit that are disconnected from the electrical requirement of actual devices. As a result, widely used metrics guide material design under conditions that can be impractical for devices. Here, we introduce a benchmarking framework to guide TCO development, in which transparent conductors are evaluated at fixed, application-relevant sheet resistance $(R_S)$. The resulting metric, $T_{app}(R_S)$, anchors comparison to device requirements, asking instead: What optical transparency can be obtained at the sheet resistance required by a given application? This approach provides a directly interpretable measure of performance, enabling materials to be benchmarked in terms of absolute transparency gains at a specified $R_S$. Applied to representative conventional and emerging TCOs, the framework defines the sheet-resistance landscape relevant to each application and maps how different materials perform within it. In doing so, it provides an application-rooted guide to material development and selection. More broadly, this approach establishes a general strategy for evaluating materials under fixed operational constraints, bridging the gap between materials design and device integration.
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Superconductivity

Superconductivity and electronic structure evolution in the enforced semimetal Fe-doped ZrTe$_2$

L. M. Ishikura, C. F. Schuch, A. Faé Rabello et al. (+6 more)

ZrTe$_2$ is an outstanding layered semimetal due to the topologically nontrivial electronic structure. In this work, we present an investigation of the electronic evolution of ZrTe$_2$ in the presence of Fe intercalation, namely Fe$_{x}$ZrTe$_2$ ($x= 0 - 0.25$), scrutinized by both experimental measurements and ab initio calculations. While the first reveals a superconducting state with a maximum critical temperature $T_c = 2.74$ K ($x=$ 0.03), the latter indicates that the topological features of the pristine ZrTe$_2$ is sensitive to the distance between Te atoms and Zr layers. Also, the intercalation of Fe does not modify the non-trivial electronic band structure unlike the band crossings are now shifted slightly below $E_{F}$. In particular, a van Hove singularity near the Fermi level for a Fe content of $x=0.125$ is observed in the density of states, indicating that the superconducting order may be associated with features of the unfolded band structure and the concomitant enhancement of the density of states at $E_F$. Finally, our results reveal that the new compound with inclusion of Fe intercalation preserves the enforced semimetal classification.
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All authors L. M. Ishikura, C. F. Schuch, A. Faé Rabello, F. F. Nogueira, L. E. Corrêa, L. R. de Faria, J. Larrea Jiménez, L. T. F. Eleno, A. J. S. Machado

Statistical Mechanics

Scaling features in the Olami-Feder-Christensen model

Naveen Kumar, Rahul Chhimpa and Avinash Chand Yadav

We consider the Olami-Feder-Christensen (OFC) model on a square lattice with open boundary conditions. The model exhibits self-organized criticality and explains the Gutenberg-Richter law observed for earthquakes. A parameter $\alpha$ controls the level of local dissipation: $\alpha<0.25$ corresponds to locally dissipative and $\alpha = 0.25$ marks locally conservative dynamics. The avalanche size distribution follows a decaying power-law, with a non-universal critical exponent. Here, we examine the local and total stress fluctuations in the OFC model for both locally conservative and dissipative dynamics. The finite-size scaling analysis of the power spectra for the stress fluctuations reveals qualitatively the same but quantitatively significantly different behavior. The dynamic exponent describing the divergence of the correlation time with system size changes from nearly ballistic in the conservative to diffusive in the locally dissipative dynamics with $\alpha = 0.21$. The local stress also exhibits a signature of nearly canonical $1/f$ noise in the intermediate regime, and $1/f^2$-type scaling dominates the high-frequency regime. We further examine the probability distribution of the difference between avalanche size and area. We find a power-law behavior with a scaling exponent close to one in the conservative OFC model. The scaling feature vanishes even for the physically relevant case $\alpha = 0.21$. To examine the robustness of such features, we also examine the same quantity in the Bak-Tang-Wiesenfeld and Manna sandpile models on a square lattice. We find that the power-law behavior survives for these systems due to locally conservative dynamics.
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Disordered Systems and Neural Networks

Cluster moves with an entropic reservoir accelerate low-temperature simulations of three-dimensional spin glasses

Claudio Chilin, Enzo Marinari, Víctor Martín-Mayor et al. (+3 more)

We present an algorithm for the simulation of three-dimensional spin glasses deep in the low-temperature phase: Parallel Tempering enhanced with Houdayer moves and with an entropic reservoir (PTHR). Although differences with the standard Houdayer algorithm are small, PTHR allows us to equilibrate a large number of samples of $L=16$ lattices with Gaussian couplings for temperatures $T\geq 0.2$. We show that the computational complexity displays better size scaling than standard Parallel Tempering. For finite sizes, our method outperforms other cluster algorithms by a speedup factor of around 64. In close analogy with standard Parallel Tempering, PTHR's computational complexity strongly relates to temperature chaos.
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All authors Claudio Chilin, Enzo Marinari, Víctor Martín-Mayor, Giorgio Parisi, Juan J. Ruiz-Lorenzo, David Yllanes