Statistical Mechanics
Optimal-work feedback on particles with activity — gliding on active fluctuations using positional information
Lars Torbjørn Stutzer and Sarah A. M. Loos
We study the minimum-work feedback control of particles subject to active fluctuations. Considering an active Ornstein-Uhlenbeck particle confined by a moving harmonic trap, we derive exact optimal protocols following an initial position measurement. Our results show that nonequilibrium correlations between position and active fluctuations allow work extraction from the activity based on positional information only, i.e., without directly measuring the active degree of freedom, which was the focus of earlier literature. We find that depending on the persistence time, activity can either facilitate or impede transport relative to passive systems. Surprisingly, unlike feedback schemes based on direct measurements of the active fluctuations, positional feedback remains energetically advantageous even in the limit of infinitely persistent activity. Our results provide design principles for information engines and optimal control strategies operating in active environments.
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Materials Science
From Goldene to Noblene: exhaustive enumeration of the ordered Au-Ag-Cu monolayer alloys
Marcelo Lopes Pereira Junior
Two-dimensional metals became a laboratory reality with the isolation of Goldene, a gold sheet one atom thick released by chemical exfoliation, which raises the question of what alloying can achieve on the same close-packed
lattice. Here we combine an exhaustive enumeration of derivative superstructures with density functional theory to map the ordered Au-Ag-Cu monolayer
alloys, relaxing every
symmetry-inequivalent arrangement up to four atoms per
cell and extending the set with larger
cells selected by a fitted model. We find that the arrangement of the atoms, and not their proportion, controls the mixing energy, since the spread among the orderings of a single composition is several times the step between neighboring compositions, one composition spans more than 50~meV/atom between two arrangements of the same three atoms, and at two compositions the arrangement decides the sign. The energetics is carried by a competition between Au-Cu contacts, which bind, and Ag-Cu contacts, which do not, and bulk enthalpies computed under the same protocol show that this chemistry is not uniformly rescaled in two dimensions, since Au-Cu orders more strongly in the monolayer than in the
crystal while the other two weaken. A pair model completed by an elastic size-mismatch term reproduces the computed energies to a few meV/atom and returns a composition landscape whose convex hull no balanced ternary composition reaches. One equimolar ordering, which we name Noblene, is the only structure in which every atom is surrounded exclusively by unlike species, and it is dynamically stable and metallic, and carries a Poisson's ratio above one half, higher than that of any of the three pure monolayers. Since Noblene sits on the
lattice that Goldene already realizes, the route that produced Goldene is a plausible starting point for its synthesis.
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Soft Condensed Matter · Cross-listed from physics.bio-ph
A viscoelastic theory for ultrasound-induced intracellular streaming
Niels Gieseler, Falko Ziebert and Ulrich S. Schwarz
Ultrasound is increasingly used to control biological
cells, but its multiple physical effects, including radiation force, streaming, heating, and cavitation, require theoretical frameworks that can quantify their relative strengths. Here we develop a semi-analytical model to predict flow patterns and energy distributions of ultrasound-induced intracellular streaming.
Cells are modeled as viscoelastic droplets immersed in a fluid with different viscoelastic properties. For this geometry, the momentum equation with an Oldroyd-B constitutive law is solved using a perturbation expansion commonly applied in acoustofluidics. The resulting equations for the different orders of the expansion are solved using partial wave expansion and explicit integration. We investigate our model for a range of parameters which is relevant both for synthetic
polymer and for
protein solutions. We find a series of flow reversals that we can connect to the distribution of energy into the different modes. We also consider density and compressibility contrasts, which shift these transitions and introduce new ones. Finally, we discuss the potential biological relevance of our mathematical results for cellular sensing and signaling.
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Soft Condensed Matter
Response of a Model Glass to Athermal Quasistatic Pinching
Takumi Nagasawa, Kirsten Martens, Jean-Louis Barrat et al. (+1 more)
We numerically investigate the mechanical response of amorphous solids to localized force dipoles, referred to as pinching, using athermal quasistatic simulations of model glasses with varying degrees of stability. We employ a control parameter, the imposed extension, corresponding to the increase in rest length between the two pinched particles relative to their initial separation. Increasing this extension allows us to continuously tune the system from the elastic to the plastic regime. For small extensions, the response remains elastic. In this regime, the displacement field induced by pinching is well described by linear elasticity and exhibits a long-range power-law decay consistent with dipolar forcing. Averaged responses display anisotropic, quadrupolar-like patterns, with quantitative agreement between simulations and analytical predictions. This continuum description remains valid down to particle-scale distances. As the imposed extension increases, the response becomes plastic. Pinching can then trigger either localized or system-spanning rearrangements, depending on glass stability. Well-annealed glasses exhibit localized plastic events, whereas poorly annealed systems display delocalized cascades. We introduce a method to extract the principal axis of plastic deformation and analyze the associated displacement fields and plastic activity. Overall, our results demonstrate that pinching provides a minimal local probe of amorphous solids. The resulting response, governed by both glass stability and imposed extension, offers insight into the interplay between elasticity, elementary rearrangements, and the emergence of collective plasticity.
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All authors Takumi Nagasawa, Kirsten Martens, Jean-Louis Barrat, Misaki Ozawa
Other Condensed Matter
Topological Lithography via External Field: Creating Topological States Anywhere Beyond the Edge
Haoran Nie, Chaoran Jiang, Xiangying Shen et al. (+1 more)
Topological
insulators (TIs), recognized for their robust boundary states and unconventional phase transitions, have emerged as one of the most impactful discoveries in recent decades, attracting considerable interest across diverse fields. However, conventional TIs require topological contrasts between adjacent bulk regions, typically achieved by distinct
symmetries, which limits their flexibility and broader applicability. In this work, we introduce a "lithography" approach to inducing topological states by applying external fields in time-reversal-symmetric systems. These states transcend the conventional bulk
topology design paradigm and offer exceptional tunability: they can exist at
geometric edges, within the bulk, or even be induced remotely. Because the external field is highly controllable, the induced states are programmable, reconfigurable, and can be easily tailored into desirable patterns. Theoretically, we demonstrate that the external field modifies the Jackiw-Rebbi mechanism, inducing a real-space topological transition characterized by a local topological marker (LTM). We further establish an extended valley bulk-edge correspondence, which explains both the conventional scenario and our findings. Our results, validated across mechanical, electronic, and acoustic platforms, highlight the broad applicability of this approach to various systems. This work not only advances the theory of
topology but also enhances the diversity, tunability, and practical implementation of topological states and materials.
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All authors Haoran Nie, Chaoran Jiang, Xiangying Shen, Lei Xu
Superconductivity
Electronic Structure and Superconductivity in La$_{1.55}$Sr$_{0.45}$CuO$_4$/La$_2$CuO$_4$ Artificial High-$T_c$ Superlattices Probed by Hard and Soft X-ray Spectroscopy
U. M. Jayathilake, S. Sheikh, T.-L. Lee et al. (+5 more)
In La$_{1.55}$Sr$_{0.45}$CuO$_4$/La$_2$CuO$_4$ (LSCO/LCO) artificial high-$T_c$ superlattices (AHTS), grown by
quantum material design, the superconducting dome can be tuned by varying the
geometric ratio $L/d$, where $L$ is the LCO layer thickness and $d$ is the superlattice nanoscale period. Here, we combine hard X-ray photoelectron spectroscopy (HAXPES) and polarization-dependent soft X-ray absorption spectroscopy (XAS) to probe how the electronic structure evolves across the $L/d$-tuned superconducting dome. We observe systematic chemical-potential
evolution across the series, together with enhanced spectral weight near the Fermi level, enhanced local and non-local screening signatures, and increased in-plane orbital polarization near the top of the dome. Together, these spectroscopic signatures provide insight into the emergence of Fano-Feshbach resonant superconductivity in the LSCO/LCO AHTS series.
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All authors U. M. Jayathilake, S. Sheikh, T.-L. Lee, C. Klewe, G. Logvenov, G. Campi, A. Bianconi, A. X. Gray
Soft Condensed Matter
Liquid-liquid phase transitions in dipolar liquids. Insights into Supercooled Water
Maria Grazia Izzo
Dipolar
liquids combine two coupled degrees of freedom, translational and dipolar. Intriguingly, these two sectors can reside in distinct thermodynamic states, with the state of one sector possibly favoring a specific state of the other. The onset of ferroelectric order in dipolar
liquids is an example of this mutual stabilization. Since this coupling is often encoded in interaction potentials, projecting out one sector to derive an effective interaction for the other can uncover the microscopic mechanism underlying this phenomenon. A coarse-grained theory in which the distance between nearest-neighbor particles depends on their dipolar interaction through a density-dependent mechanical compliance shows that a ferroelectric transition can trigger a
liquid-
liquid transition. It also predicts a first-order
liquid-
liquid transition in the paraelectric phase that can in turn induce ferroelectric ordering. The anisotropic dipolar-dependent soft-core interaction is shown to lead to an effective Jagla-like isotropic two-length-scale interaction, known to support
liquid-
liquid phase transitions. Here, however, the two-length-scale pattern depends on density and dipolar configuration, becoming sensitive to dipolar order. Analysis of supercooled TIP4P/Ice water numerical simulations shows that first-coordination-shell features of pair correlation functions are sensitive to dipolar interaction, supporting the coarse-grained theory foundations. Comparison of low- and high-density
liquid water reveals enhanced spatial anisotropy of the first coordination shell in the low-density
liquid, with increased effective excluded volume, showing that the
liquid-
liquid transition involves structural changes within the first shell, beyond reorganization of the interstitial region and tetrahedral order. These findings point to a role for dipolar interactions in supercooled water
liquid-
liquid phase transition.
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Statistical Mechanics
Survival in a partially reactive wedge
Denis S. Grebenkov
We investigate the power-law decay of the survival probability of a Brownian particle diffusing in an infinite planar wedge whose two sides are partially reactive and described by Robin boundary conditions. We employ matched asymptotic analysis to relate the long-time asymptotics to a stationary harmonic Robin problem near the apex. This approach determines the persistence exponent for arbitrary opening angles and yields the prefactor explicitly for the family of wedges with $\alpha=\pi/n$ ($n=1,2,\ldots$). A simple extension of the apex prefactor to arbitrary angles is conjectured and supported numerically. This asymptotic behavior describes the crossover to the well-known result for perfectly absorbing wedges. As immediate applications, we also deduce the long-time behavior of the probability density function of the boundary local time on wedge sides, as well as the probability density function of the associated first-crossing time.
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Soft Condensed Matter
XPCS-Echo and broad relaxation measurements using a bunch-mode data acquisition scheme
William Chèvremont, Thomas Gibaud, Yuriy Chushkin et al. (+1 more)
Echoes observed in the intensity-intensity autocorrelation functions [$g_2(q, \tau)$] is a powerful method for probing nonaffine deformations and yielding behavior of soft viscoelastic materials subjected to an oscillatory shear. Multispeckle X-ray
photon correlation spectroscopy (XPCS) measurements of large number of echoes with high time resolution impose severe constraints in terms of the computational hardware and potential degradation of the sample. These issues are alleviated by implementing a bunch-mode data acquisition scheme in which the highest resolution frames or bunches centered at the echo peaks. In addition, by placing the bunches in an aperiodic Fibonacci sequence, $g_2(q, \tau)$ over a long time span can be measured with orders of magnitude lesser number of frames. The performance of these XPCS acquisition schemes is demonstrated using slowly relaxing model colloidal suspensions. Furthermore, an analytical expression is provided for the quantitative description of full $g_2(q, \tau)$.
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All authors William Chèvremont, Thomas Gibaud, Yuriy Chushkin, Theyencheri Narayanan
Quantum Gases
Dynamical stabilisation of a quantum fluid using a single topological defect
Deborah Capecchi, Paolo Comaron, Antonio Gianfrate et al. (+5 more)
The size and shape of a
quantum fluid in
equilibrium is strongly influenced by the inter-particle interactions. In the attractive interaction regime, atomic
quantum fluids ultimately collapse in a violent process that expels most of the particles from the macroscopically occupied state. Here, we use a
quantum fluid of light in propagating geometry as an analogue to a two-dimensional Bose-Einstein condensate (BEC) with large attractive interactions to show that non-trivial
topology significantly alters the dynamical behaviour of the collapse, enhancing the BEC stability and delaying the collapse time by an order of magnitude. We measure direct experimental signatures of
topology affecting
quantum hydrodynamics, unveiling the inherent competition between attractive nonlinearities, that lead to the collapse, and the preservation of topological charge from a multi-charged
vortex. We fully characterise the collapse process in coordinate space and the eventual `solitonification' of the system and connect it to the mode structure of the excitation spectrum.
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All authors Deborah Capecchi, Paolo Comaron, Antonio Gianfrate, Milena De Giorgi, Dario Ballarini, Daniele Sanvitto, Franco Dalfovo, Dimitrios Trypogeorgos
Materials Science
Spin Hall Magnetoresistance in Antiferromagnetic Insulators
Stephan Geprägs, Matthias Opel, Johanna Fischer et al. (+4 more)
Antiferromagnetic materials promise improved performance for spintronic applications, as they are robust against external
magnetic field perturbations and allow for faster magnetization dynamics compared to ferromagnets. The direct observation of the antiferromagnetic state, however, is challenging due to the absence of a macroscopic magnetization. We show that the
spin Hall magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic
spin structure via simple electrical transport experiments by investigating the easy-plane antiferromagnetic
insulators alpha-Fe2O3 (hematite) and NiO in bilayer
heterostructures with a Pt heavy-metal top electrode. While rotating an external
magnetic field in three orthogonal planes, we record the longitudinal and the transverse resistivities of Pt and observe characteristic resistivity modulations consistent with the SMR effect. We analyze both their amplitude and phase and compare the data to the results from a prototypical collinear ferrimagnetic Y3Fe5O12/Pt bilayer. The observed
magnetic field dependence is explained in a comprehensive model, based on two
magnetic sublattices and taking into account
magnetic field-induced modifications of the domain structure. Our results show that the SMR effect allows to readout the
spin configuration and to investigate magnetoelastic effects in antiferromagnetic multi-domain materials. We demonstrate that the SMR amplitude scales with the sum of the absolute sublattice magnetizations in ferrimagnetic and antiferromagnetic materials. In alpha-Fe2O3/Pt bilayers, we find an unexpectedly large SMR amplitude of 2.5E-3, twice as high as for prototype Y3Fe5O12/Pt bilayers, making the system particularly interesting for room-temperature antiferromagnetic spintronic applications.
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All authors Stephan Geprägs, Matthias Opel, Johanna Fischer, Philipp Schwenke, Matthias Althammer, Hans Huebl, Rudolf Gross
Mesoscale and Nanoscale Physics
Nonreciprocal Magnon Hanle Effect in Antiferromagnetic $\alpha$-Fe$_2$O$_3$
Janine Gückelhorn, Sebastián de-la-Peña, Monika Scheufele et al. (+8 more)
The precession of the
magnon pseudospin about the
equilibrium pseudofield, the latter capturing the nature of magnonic eigenexcitations in an antiferromagnet, gives rise to the
magnon Hanle effect. Its realization via electrically injected and detected
spin transport in an antiferromagnetic
insulator demonstrates its high potential for devices and as a convenient probe for
magnon eigenmodes and the underlying
spin interactions in the antiferromagnet. Here, we observe a non-reciprocity in the Hanle signal measured in alpha-Fe2O3 using two spatially separated Pt electrodes as
spin injector and detector. Interchanging their roles alters the detected
magnon spin signal. The recorded difference depends on the applied
magnetic field and reverses sign when the signal passes its nominal maximum at the so-called compensation field. Our findings unlock the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena.
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All authors Janine Gückelhorn, Sebastián de-la-Peña, Monika Scheufele, Matthias Grammer, Matthias Opel, Stephan Geprägs, Juan Carlos Cuevas, Rudolf Gross, Hans Huebl, Akashdeep Kamra, Matthias Althammer
Materials Science
Colossal reversible conductivity switching by room-temperature oxygen-vacancy ordering in Aurivillius oxide films
Song Zhou, Songge Zhang, Lanting Shi et al. (+11 more)
Oxygen vacancies are central to the functionality of oxides, yet they typically exist as randomly distributed point defects, limiting the ability to precisely manipulate their collective behavior. Here, we report the room-temperature formation of a long-range-ordered oxygen-vacancy superstructure in single-crystalline Aurivillius-phase Bi2WO6 thin films via a mild nitrogen-
plasma treatment. This structural transformation unlocks a colossal, reversible modulation of electrical conductivity by more than nine orders of magnitude, accompanied by a striking optical transition from transparent to black. Atomic-resolution imaging and spectroscopy reveal that the vacancies selectively order within the perovskite-like tungsten oxide layers, forming a coherent defect
lattice that is absent in the pristine film. Oxygen-
plasma treatment removes the vacancy superstructure and restores the initial state, whereas subsequent nitrogen-
plasma treatment reconstructs it, enabling repeatable room-temperature switching between distinct structural, electronic and optical states. The phenomenon is also observed in another Aurivillius member, Bi2MoO6, suggesting its generality across the Aurivillius family. These findings establish a new paradigm for atomic-scale defect engineering - using gentle
plasma chemistry to construct ordered defect
lattices, opening avenues for reversible property modulation in complex oxides.
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All authors Song Zhou, Songge Zhang, Lanting Shi, Ping Zhang, Na Li, Jiawei Huang, Bolin Meng, Chuangye Song, Shaoxiang Sheng, Yang Chai, Lede Xian, Jinxing Zheng, Guangyu Zhang, Kehui Wu
Soft Condensed Matter
Pure FENE Bond Potential for Soft Matter and Biological Simulations: Theory, HOOMD-blue Implementation, and Applications to Polymer, Colloidal, and Membrane Systems
Anirban Polley
The finitely extensible nonlinear elastic (FENE) potential is widely used as a bonded interaction in coarse-grained simulations of
polymers, soft matter, colloids, and biological systems. In the classical Kremer–Grest framework, FENE bonding is combined with a short-range Weeks–Chandler–Andersen (WCA) interaction to provide finite bond extensibility together with excluded-volume repulsion. Although this combination is highly successful, it intrinsically couples bonded elasticity to the nonbonded interaction, limiting the ability to independently control these two contributions. Here, we introduce a standalone FENE bond potential in HOOMD-blue in which finite bond extensibility is implemented independently of the choice of nonbonded interaction. This formulation allows the same FENE bond potential to be combined with WCA, Lennard–Jones, or other pair interactions without modifying the bonded interaction itself. We demonstrate the utility of the standalone formulation in coarse-grained
polymer chains, colloidal networks, and mesh-based biological membrane models. Across these systems, Pure FENE bonding without short-range excluded-volume stabilization produces pronounced structural contraction, whereas the addition of WCA repulsion suppresses this collapse and preserves finite, spatially extended structures. These results demonstrate that separating finite bond extensibility from steric interactions provides independent control over local bond mechanics and collective structural organization. The standalone FENE formulation therefore provides a modular framework for coarse-grained simulations in which molecular connectivity and nonbonded interactions represent distinct physical mechanisms.
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Statistical Mechanics
Thermodynamic optimization of thermal landscapes and energy barriers in a Brownian heat engine
Mesfin Taye
Spatial temperature fields in Brownian heat engines are commonly prescribed a priori, and the resulting transport and thermodynamic properties are then calculated. Here we formulate the complementary inverse-design problem: determining the temperature profile and barrier height that optimize a chosen thermodynamic objective. We consider an overdamped Brownian particle in a symmetric triangular periodic potential under a constant opposing load and derive the exact stationary current and probability density for an arbitrary bounded temperature field, $\Tc\le T(x)\le\Th$. In the quasistatic limit, the efficiency becomes an exact functional of two inverse-temperature integrals over the uphill and downhill branches. Its rigorous global maximum under the pointwise temperature bounds is $\eta_{\max}=1-\Tc/\Th$, attained uniquely, up to sets of measure zero, by the hot-uphill/cold-downhill piecewise-constant profile. At finite current, however, the optimization changes qualitatively because the current is determined jointly by the cycle affinity and a nonlocal transport resistance. We derive the exact functional gradient and the corresponding box-constrained optimality conditions, showing that the current- or power-maximizing profile generally differs from the quasistatic efficiency optimum. For any prescribed temperature field, the current-maximizing barrier satisfies an exact balance between the marginal gain in thermal rectification and the marginal increase in transport resistance, with the characteristic estimate $U_0^*\simeq T_{\rm act}$, where $T_{\rm act}^{-1}=(2/L)\int_0^{L/2}\dd x/T(x)$.
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Soft Condensed Matter
The Universal Role of Fragility on the Yielding Transition of Active Glass under Oscillatory Shear
Arnab Mandal, Roni Chatterjee and Smarajit Karmakar
The yielding transition marks the onset of irreversible plastic deformation in amorphous solids and plays a central role in determining the mechanical stability and failure of metallic glasses, colloidal suspensions, and biological assemblies. Despite extensive research, the microscopic factors governing the nature of yielding, particularly the transition between brittle and ductile mechanical responses, remain poorly understood. Recent studies have identified kinetic fragility as a key parameter governing yielding in passive glasses; whether this connection persists in active glasses remains open. Here, using molecular dynamics simulations of a Kob-Andersen glass former doped with Run-and-Tumble (RTP) active particles under oscillatory shear, we show that activity systematically reduces kinetic fragility and consequently alters the mechanical response. The common yield point $\gamma_c$ decreases monotonically with activity and exhibits a power-law dependence on the Arrhenius activation barrier. Increasing activity suppresses the dependence of the yield strain on thermal history and transforms the response from brittle-like to increasingly ductile, with smoother stress relaxation and reduced stress discontinuities. The timescale to reach steady state near yielding retains a critical power-law divergence, indicating that activity does not alter the underlying critical character of the transition. Active glasses also develop broader, more diffuse shear bands. Our results establish kinetic fragility as a unifying parameter governing yielding in both passive and active glasses and demonstrate that activity offers a powerful route to tune the mechanical response of amorphous materials.
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Soft Condensed Matter
Multivariate hyperdensity functional theory for inhomogeneous equilibrium fluids: From first principles to simulation-based machine learning
Florian Sammüller and Matthias Schmidt
Hyperdensity functional theory facilitates the investigation of the
equilibrium behavior of a general order parameter or statistical mechanical observable in spatially inhomogeneous classical many-body systems. The approach is based on applying the exact Mermin-Evans classical density functional mapping to an extended ensemble. Here we present the multivariate generalization for investigating simultaneously the properties and interrelations of several different hyperobservables of choice. The resulting framework gives rise to a systematic characterization and prediction scheme for general many-body phenomena. All pertinent
equilibrium averages, variances, and covariances constitute universal density functionals, as we demonstrate explicitly. Associated one-body hyperfluctuation profiles quantify the degree of correlation of the local density with first- and second-order combinations of hyperobservables. These multivariate hyperfluctuation profiles are accessible in many-body simulations and they satisfy exact hyper-Ornstein-Zernike equations, which we derive from the minimization principle in the extended multivariate ensemble. The formal structure of the theory integrates naturally with supervised machine learning, which renders all hyperdensity functionals accessible in practice via training of neural networks on simulation data. We demonstrate all salient techniques using the illustrative case of clustering in confined hard rod fluids, thereby choosing the total number of particles and the largest cluster size as the representative hyperobservables of interest. Our numerical methodology enables the efficient and successful prediction of all statistical quantities induced by the chosen hyperobservables, which we verify via comparison to test data and which we attribute to the tight interplay of first-principles and machine-learning concepts that our general approach combines.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Exceptional Topological Signatures of Non-Hermitian Photonic Hopf-Link Braids
Samit Kumar Gupta
Non-Hermitian physics endows the non-Abelian systems with exceptional
topology characterized by non-commutative braid patterns. Interplay of distinct competing sources of non-Hermiticity may induce novel topological effects. Here, we provide a generalized Hatano-Nelson model with higher-order nonreciprocal hoppings, non-Abelian gauge fields, and staggered gain-loss processes showing the exceptional topological structure of the Hopf-link braids that undergoes a EP-mediated topological phase transition. We demonstrate that mixing multiple nonreciprocal channels drives the system into highly intricate, nested complex energy Hopf-link braids and expands the topological landscape up to higher-order braiding sectors. Furthermore, utilizing biorthogonal eigenvector tracking, we map the structural
evolution of the exceptional phase boundaries via the maximum Petermann factor in the phase angle parameter planes. We show that the gain-loss non-Hermiticity drives a topological crossover where the extended exceptional contours constrict into isolated regimes. The demonstration of EP-mediated topological phase transition of Hopf-link braids and the associated rich exceptional phase portraits may offer new physical insights with promising applications in robust, fault-tolerant communication channels and
quantum computing platforms.
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Statistical Mechanics
Memory-driven Topological Defects and Unconventional Long-Range Order
Ziyang Ding and Zi Cai
We investigate many-body systems with time-delayed self-interactions mediated by a
memory-feedback mechanism. We show that such temporal interactions generate non-
equilibrium orders and unique topological defects absent in
equilibrium-specifically, helical
vortices wherein opposite vorticities propagate in reverse directions along domain walls. In one dimension,
memory feedback stabilizes true long-range order against weak noise, thereby circumventing the Mermin-Wagner
theorem and resulting in an unconventional finite-temperature phase transition with a dynamical exponent $z = 4$. Physical realizations of these
memory-driven non-
equilibrium systems using active mechatronic metamaterials has also been proposed. These results demonstrate engineered temporal interactions as a powerful paradigm for non-
equilibrium many-body physics.
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Quantum Gases
Magnetic-Field-Calibration-Free Determination of the Hyperfine Constant $A$ in Ultracold Fermi gases of $^{40}$K
Yajing Yang, Biao Shan, Yuhang Zhao et al. (+8 more)
Hyperfine constant $A$ is a key parameter of the hyperfine structure and underpins precision spectroscopy and metrology. In this Letter, we develop a
magnetic-field-calibration-free method for determining the ground-state hyperfine constant $A$ in an ultracold $^{40}$K Fermi gas by utilizing a pair of magnetically insensitive ("clock") transitions. This overcomes the stringent
magnetic-field calibration requirements of conventional methods. We measure the transition frequency between these two magnetically insensitive transitions with Hz-level resolution over a range of
magnetic fields, and obtain the ground-state hyperfine constant $A = -h\times 285.730536(2)\,\mathrm{MHz}$, corresponding to an absolute uncertainty of about $2\,\mathrm{Hz}$. Our value reduces the uncertainty by nearly three orders of magnitude compared with previous determinations, providing a substantially improved reference for high-precision spectroscopy and metrology with $^{40}$K.
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All authors Yajing Yang, Biao Shan, Yuhang Zhao, Jiahui Shen, Zhuxiong Ye, Liangchao Chen, Zengming Meng, Pengjun Wang, Wei Han, Jing Zhang, Lianghui Huang
Mesoscale and Nanoscale Physics
Direct Observation of the Zigzag Edge States of a Supramolecular Diatomic Kagome Lattice
Ryohei Nemoto, Xiangzhi Meng, Behzad Mortezapour et al. (+11 more)
Lattice geometry plays a fundamental role in the behavior of Bloch electrons in a
crystal. The diatomic Kagome
lattice, an extension of the honeycomb and Kagome
lattices, is predicted to give rise to emergent and topological phenomena, but its experimental investigation has been limited thus far. Here, we fabricate a diatomic Kagome
lattice through self-assembly of a triptycene derivative with phenazine moieties (Trip-Phz)—a $\mathrm{C_3}$-symmetric, non-planar $\pi$-conjugated molecule. Our scanning tunneling microscopy (STM) observations show that Trip-Phz forms a highly ordered diatomic Kagome
lattice terminated by zigzag-type edges on the Pb(111) surface. Combined STM measurements and tight-binding calculations provide direct evidence for the existence of the edge states that correspond to those of
graphene. These states are topological edge states dictated by the quantization of the Zak phase and the bulk-edge correspondence.This work reveals an ideal platform for exploring
quantum materials with unique
lattice geometries using supramolecular technology.
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All authors Ryohei Nemoto, Xiangzhi Meng, Behzad Mortezapour, Alexander Weismann, Saya Nakano, Masahisa Tsuchiizu, Ryuichi Arafune, Noriaki Takagi, Sho Nakamura, Katsunori Wakabayashi, Rie Suizu, Richard Berndt, Takashi Uchihashi, Kunio Awaga
Materials Science
All-dry processing of 3C-SiC nanomechanical string resonators for extreme aspect ratios and high intrinsic quality factor
Felix David, Philipp Bredol, Yannick S. Klaß et al. (+1 more)
Conventional fabrication of suspended nanomechanical resonators typically relies on wet-chemical process steps and critical point drying, which can compromise sample yield and cleanliness. Here, we present an all-dry fabrication process for strongly stressed 3C-SiC nanomechanical string resonators that entirely avoids wet-chemical etching and cleaning. Using a negative-tone electron-beam resist as an etch mask and a three-step reactive-ion etching process for both structuring and release, we achieve high fabrication yield, clean suspended structures, and extreme aspect ratios of 8.500. We perform full mechanical characterization of the resulting doubly-clamped nanostring resonators, and establish a
benchmark intrinsic quality factor for dissipation-diluted 3C-SiC of Qintr = 4.200.
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All authors Felix David, Philipp Bredol, Yannick S. Klaß, Eva M. Weig
Materials Science
A Wannier-first approach for extended chiral systems
Yashpal Singh, Juan E. Peralta, Koblar A. Jackson et al. (+1 more)
We present a real-space formulation of DFT for extended systems in which localized Wannier-like functions are constructed directly from localized Gaussian basis functions without explicitly computing canonical Bloch-like states during the self-consistent cycle. Building on the formalism of Pederson and Lin [Phys. Rev. B 35, 2273 (1987)], a variational set of Wannier-like functions is generated self-consistently within a finite Wannier domain and used to construct the charge density, electrostatic potential, and per
cell total energy of the extended system. The occupied space can be determined entirely from the Wannier-like functions. Electronic band structures can be recovered in a post-processing step by solving the full
Hamiltonian in a Bloch-like basis constructed from Gaussian orbitals. A key feature of the method is that it can incorporate combined translation–rotation, or screw,
symmetries, enabling efficient simulations of chiral and helical systems with finite twist angles at essentially the same computational cost as systems described by pure translational
symmetry. The approach is validated through calculations on linear and twisted $\mathrm{{-}C{\equiv}C{-}}$ and $\mathrm{{-}Li{-}F{-}}$ chains, as well as
graphene, where total energies and band structures show excellent agreement with reference periodic calculations. To illustrate the ability of the method to treat three-dimensional systems, it is further applied to AA graphite, in which carbon atoms in adjacent
graphene layers are aligned directly above one another, as well as helically stacked AA graphite structures. The Wannier-first framework provides a practical route for treating extended systems with nontrivial translational, rotational, and screw
symmetries, and provides a natural foundation for the implementation of orbital-dependent functionals such as the Perdew–Zunger self-interaction correction.
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All authors Yashpal Singh, Juan E. Peralta, Koblar A. Jackson, Mark R. Pederson
Statistical Mechanics · Cross-listed from hep-th
Universal fingerprint of topological defect cores
Zi-Qiang Zhao, Nayun Jia, Zhang-Yu Nie et al. (+3 more)
Topological defects are ubiquitous in physics, arising from condensed matter physics to the early universe. Although there exist many universal scaling laws for correlations between topological defects, such as Porod scaling, the fingerprint of topological defect cores has remained largely unexplored. Here, we discover a universal scaling law in the region $k>1/\xi$, where $\xi$ is the healing length of the topological defects, taking the scaling of the form factor $S_f \propto k^{-(d+p+2)}$, where $d$ is the spatial dimension and $p$ is the defect codimension. We analytically prove that this exponent originates from a universal V-shaped cusp at the defect core and is independent of the underlying system and dynamics. Numerical simulations verify this scaling law in four typical frameworks: the time-dependent Ginzburg-Landau and Gross-Pitaevskii equations in the weak-coupling regime, the gauge/
gravity duality model in the strong-coupling regime, and the Klein-Gordon equation in the Friedmann-Robertson-Walker background in cosmology. Our work provides a new probe for studying topological defects in systems ranging from
superconductors to cosmological phase transitions.
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All authors Zi-Qiang Zhao, Nayun Jia, Zhang-Yu Nie, Hua-Bi Zeng, Jing-Fei Zhang, Xin Zhang
Statistical Mechanics
Branching stochastic mechanics: Relative localization and collective poles from Bohm/Fisher feedback
Benoit Bischoff and Eric Dumonteil
Branching
stochastic mechanics (BSM) provides a reciprocal branching representation of the Schrödinger–Nagasawa pair. Its centered forward–backward kernel $C_{\rm FB}=\mathbb E_\omega[\psi_F\psi_B]$ resolves an organized connected sector, with weight $\rho_{\rm BSM}=-C_{\rm FB}(x,x)$ on the anticorrelated branch. Here we investigate how this sector forms, localizes, and propagates under Bohm/Fisher feedback. We retain the branching covariance on the prescribed background as the bare noise kernel and truncate the nonlinear interaction to Bohm/Fisher drift vertices. A Martin–Siggia–Rose–Janssen–de Dominicis formulation and a causal two-loop two-particle-irreducible (2PI) closure determine response and correlation functions self-consistently. While the free connected theory exhibits secular growth and ultraviolet accumulation, the dressed theory develops a finite relative screening length. A reduced numerical
evolution shows bounded formation of the localized sector, and a self-similar Fisher construction defines a saturated information velocity $c_\star$. A Born–Oppenheimer separation connects this internal organization to collective propagation. The instantaneous adiabatic kernel has two pole families at fixed internal momentum: a gapless difference branch and a gapped sum branch. Projecting both inverse response kernels onto the same localized internal profile defines their collective coefficients. If both propagation speeds match $c_\star$ and the projected gap matches $mc_\star^2/\hbar$, the gapped branch takes the infrared Klein–Gordon form. These matching conditions define a candidate relativistic fixed point whose dynamical realization remains to be tested.
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Strongly Correlated Electrons
Disorder-driven competing magnetic interactions and glassy magnetic behavior in quaternary Heusler alloy FeRuMnGe
Manikantha Panda, Prabuddha Kant Mishra, Sonali S. Pradhan et al. (+6 more)
In this combined experimental and theoretical study, we investigate the role of disorder in governing the
magnetic ground state of the quaternary Heusler
alloy FeRuMnGe. In the FeRuMnZ (Z = Ga, Si) series, chemical substitution modifies atomic ordering and electronic structure, resulting in distinct
magnetic ground states. Motivated by this, we extend the series to FeRuMnGe. X-ray diffraction reveals B2-type antisite disorder, where Fe–Ru and Mn–Ge intermix. Theoretical calculations show that such disorder modifies exchange interactions, leading to competing ferromagnetic and antiferromagnetic couplings, and drives the system from half-metallic to metallic.
Magnetic measurements reveal competing interactions, giving rise to a cluster-glass state coexisting with long-range
magnetic order. The absence of a thermodynamic signature at $T_f$, together with ac susceptibility and relaxation measurements, supports the presence of short-range
magnetic interactions and a glassy
magnetic state. The compound exhibits an enhanced
magnetic response below $\sim 161$ K and a maximum magnetization of $\sim 1.64~\mu_B$/f.u. at 5 T. Overall, this work establishes a direct correlation between antisite disorder, competing exchange interactions, and glassy magnetism in quaternary Heusler
alloys. Combined experimental results and theoretical calculations reveal that disorder drives the system from an AFM-dominated state in FeRuMnSi to an FM-dominated state in FeRuMnGe, providing deeper insight into the role of the extent of disorder in governing the
magnetic properties of QHAs.
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All authors Manikantha Panda, Prabuddha Kant Mishra, Sonali S. Pradhan, Aarti Gautam, Bhagyashree Pol, P D Babu, Ashok Kumar Ganguli, V. Kanchana, Tapas Paramanik
Materials Science
'pySNOW': a Python Suite for the NanO-World
Sofia Zinzani, Gilberto Nardi, Giacomo Becatti et al. (+4 more)
In computational materials science, numerical simulations are indispensable tools for revealing atomic-scale processes. For building blocks of the nanoworld, such as nanoparticles and nanoalloys, atomistic simulations provide detailed insight into their behaviour under diverse conditions. These simulations enable the study of formation and growth mechanisms, transport phenomena, chemophysical stability, and chemical reactions, including catalytic processes. To unravel the complex structure–property relationships that characterise nanoobjects, it is crucial to develop robust and insightful representations of their atomistic structure at global and local scales. Such descriptions enhance our understanding of nanoparticle behaviour and play a key role in guiding their rational design in silico for targeted applications.
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All authors Sofia Zinzani, Gilberto Nardi, Giacomo Becatti, Davide Alimonti, Letícia F. Basso, Kevin Rossi, Francesca Baletto
Statistical Mechanics · Cross-listed from math.PR
Generalised Random Parking for Trapeziums on a Strip
David Kramer-Bang and Stjepan Šebek
In this article, we study a generalisation of Rényi's car-parking problem in which isosceles trapeziums are sequentially deposited on a strip. We derive an explicit formula for the parking constant in terms of the lengths of the two bases, recovering the classical rectangular and triangular models as special cases. We further obtain quantitative finite-size asymptotics for both the expected number and the variance of deposited trapeziums, with convergence rates that depend explicitly on the geometry of the deposited particle. In particular, although the recursive construction involves two different substrate geometries, their variances have the same leading asymptotic density. Finally, we show that the parking constant depends non-monotonically on the ratio of the two base lengths and possesses a unique minimiser, so that the least efficient shape is a genuine trapezium rather than a triangle.
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Quantum Gases · Cross-listed from math-ph
Precise spectral asymptotics, exponential localization, and spectral gap estimates for the three-boson lattice Schrödinger operator
Janikul Abdullaev, Abdumalik Eshniyozov, Abdikhurayra Toshturdiev et al. (+1 more)
We study three identical
bosons with contact attraction of strength mu on the square
lattice at total quasimomentum K = 0 and K = pi. First, at K = 0, for all sufficiently large mu there are exactly two
eigenvalues below the essential spectrum. The trimer branch follows from Kato perturbation theory at the simple isolated
eigenvalue 3 of the pair-contact operator, uniformly in K; the atom-dimer branch follows from a Feshbach-Schur reduction whose limiting equation coincides with the second Birman-Schwinger (Faddeev)
eigenvalue of the finite-rank principal part. The spectral gap between the two branches grows linearly in mu. Second, at K = pi the trimer branch is unchanged up to O(mu^-2), the two-particle threshold equals -mu + 4 exactly, and the gap to it is 2mu - 2 plus lower order corrections. The second bound state disappears because the exchange operator changes sign, S_pi = -S_0: the s-channel
eigenvalue that exceeds 1 at K = 0 becomes negative, while the only positive atom-dimer channel at K = pi is the odd p-channel, bounded by 2 - 4/pi < 1. Consequently the operator has exactly one
eigenvalue below the threshold minus 36/(mu - 10). Third, the ground state is exponentially localized in the relative coordinates. The decay exponent is positive unconditionally; under a non-cancellation hypothesis it is bounded above by log(3mu) plus lower order terms, while finite-volume computations indicate the slowest tail is the atom-dimer dissociation channel with decay rate one half log(2mu). A dictionary between the principal-part method, Kato theory, and the atom-dimer threshold
matrix is given, together with the three-dimensional constants for comparison.
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All authors Janikul Abdullaev, Abdumalik Eshniyozov, Abdikhurayra Toshturdiev, Mikhail Dolgopolov
Materials Science
Spin wave freezing in Re/Co/Pt multilayers
Jan Kisielewski, Kilian Lenz, Pawel Gruszecki et al. (+7 more)
The phenomenon of
spin wave (SW) freezing occurs in the Damon-Eshbach mode in thin film
magnetic systems, when SW phase and group velocities both go to zero, and the wave ceases to oscillate and move, preserving its shape as a domain structure pattern. This effect is related to the
spin reorientation transition, where the magnetization configuration changes between the homogeneous in-plane state and domain structure with the out-of-plane magnetization component state. Here, we study the SW freezing effect in [Re/Co/Pt]$_{20}$
magnetic multilayers, induced by varying the in-plane external
magnetic field. The studies were performed on nanostructures with the quality factor $Q$ (ratio of uniaxial anisotropy to demagnetization energies) greater and smaller than one. Domain structures with an out-of-plane magnetization component were observed in these multilayers. The critical field, visible as the saturation field $H_s^{||}$ in the parallel static magnetization curve measured by superconducting
quantum interference device (SQUID), is also manifested in the field-dependent vector-network-analyzer ferromagnetic resonance (VNA-FMR) experiment, which measures the homogeneous magnetization oscillations. Brillouin Light Scattering (BLS) spectra, recorded for several values of wave vectors and several field values, probed the field-
evolution of the dispersion relation. Micromagnetic simulations allow one to obtain a full dispersion, in good agreement with VNA-FMR and BLS results. Around $H_s^{||}$ the simulated dispersion relations approach the conditions for SW freezing. Below $H_s^{||}$ low and high frequency VNA-FMR modes are related to magnetization oscillations inside domain walls and within domains, respectively. The experimental results of static and dynamic behavior, together with micromagnetic simulations, create an overall consistent picture of the investigated multilayers.
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All authors Jan Kisielewski, Kilian Lenz, Pawel Gruszecki, Ryszard Gieniusz, Urszula Guzowska, Marek Kisielewski, Artem Lynnyk, Aleksiej Pietruczik, Andrzej Wawro, Andrzej Maziewski