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Physics Condensed Matter

cond-mat Watch Condensed Matter

Thursday 9 October

Mesoscale and Nanoscale Physics

Three-Dimensional Electrostatic and Quantum-Confinement Modeling of Silicon Nanowire Double Quantum Dots

Nilesh Pandey, Dipanjan Basu, Leonard F Register et al. (+1 more)

We present a three-dimensional simulation study of silicon nanowire double quantum dots (DQDs) with leads at T = 2 K, which extends beyond traditional effective mass or quasi-1D and quasi-2D approaches typically applied to bulk or planar geometries. A 3-D Poisson solver is self-consistently coupled to 2-D Schrodinger along slices normal to transport (width * thickness) to obtain spatially varying subbands and wavefunctions at T = 2 K. The slice approximation is justified by the large aspect ratio (Ltot/W > 20) and by the small (< 1.2 percent) wavefunction variation observed along the transport direction. The resulting effective conduction-band profile is imported into a full-wave, open-boundary Schrodinger solver to compute the transmission spectrum T(E), and the tunnel coupling (tc) is evaluated from the bonding and antibonding splitting of the first two resonances in T(E). The simulations show that narrow dots (W = 5 nm) provide strong confinement and robust single-electron localization but require higher plunger-gate voltage, whereas wider dots (W = 20 nm) load electrons at lower bias but form shallower, more delocalized states. The tunnel coupling decreases as the dot width and length are increased, due to the reduced wavefunction overlap between the dots, and saturates once W > 2LPG, when longitudinal confinement is dominated by the plunger gate length. The simulated tunnel coupling trend agrees with experimental data reported for the Si DQD device.
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All authors Nilesh Pandey, Dipanjan Basu, Leonard F Register, Sanjay K Banerjee

Mesoscale and Nanoscale Physics

Phase-controlled quantum transport signatures in a quantum dot-Majorana hybrid ring system

Sirui Yu, Junrong Wang, Huajin Zhao et al. (+2 more)

We investigate the quantum transport in a hybrid ring system consisting of a quantum dot (QD) coupled to two Majorana bound states (MBSs) hosted in a topological superconducting nanowire, threaded by a magnetic flux. Utilizing the dissipaton equation-of-motion approach, we demonstrate that the differential conductance shows periodic behavior and its periodicity depends on both the QD energy level and the MBS overlapping. A zero-bias peak (ZBP) emerges as a result of the balance between normal and anomalous tunneling processes, associated with the presence of a single MBS. Beyond the phase-dependent periodic behavior, the shot noise exhibits voltage-dependent transitions between sub-Poissonian ($F = 0.5$), Poissonian ($F = 1$), and super-Poissonian ($F > 1$) regimes. Strikingly, we find a giant Fano factor ($F\gg1$) emerging at the balance point, accompanied by a peak in the shot noise. This distinctive feature may serve as a supplementary signature for MBS detection. However, both ZBP in the differential conductance and shot noise peak are degraded by thermal effects.
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All authors Sirui Yu, Junrong Wang, Huajin Zhao, Hong Mao, Jinshuang Jin

Statistical Mechanics

Cell State Transitions Beyond the Small-Noise Limit

Jianzhe Wei, Jingwen Zhu, Pan Chu et al. (+2 more)

State transitions are fundamental in biological systems but challenging to observe directly. Here, we present the first single-cell observation of state transitions in a synthetic bacterial genetic circuit. Using a mother machine, we tracked over 1007 cells for 27 hours. First-passage analysis and dynamical reconstruction reveal that transitions occur outside the small-noise regime, challenging the applicability of classical Kramers' theory. The process lacks a single characteristic rate, questioning the paradigm of transitions between discrete cell states. We observe significant multiplicative noise that distorts the effective potential landscape yet increases transition times. These findings necessitate theoretical frameworks for biological state transitions beyond the small-noise assumption.
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All authors Jianzhe Wei, Jingwen Zhu, Pan Chu, Liang Luo, Xiongfei Fu

Strongly Correlated Electrons

Chiral Edge Excitations of $\nu=1/2$ Fractional Chern Insulators in the Bosonic Hofstadter Model

Xiao-Han Yang, Ji-Yao Chen and Xiao-Yu Dong

Edge excitations are the defining signature of chiral topologically ordered systems. In continuum fractional quantum Hall (FQH) states, these excitations are described by the chiral Luttinger liquid ($\chi$LL) theory. Whether these field theory predictions can be precisely identified in discrete lattice systems of finite width, however, remains a longstanding question. Here we numerically demonstrate that the charge-one edge spectral function of a $\nu=1/2$ FCI on an infinitely long strip with width $L_y=10$ quantitatively follows the predictions of $\chi$LL theory. The edge spectrum is gapless, chiral, and linear, with spectral weight increasing linearly with both momentum and energy. We further analyze the influence of lattice size, particle number, trapping potential, and charge sector of excitations on the edge properties. Our results establish a clear correspondence between lattice FCIs and continuum FQH systems and provide guidance for future experimental detection of chiral edge modes.
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Materials Science

Dimension- and Facet-Dependent Altermagnetic Biferroics and Ferromagnetic Biferroics and Triferroics in CrSb

Long Zhang and Guoying Gao

Altermagnets have recently garnered significant interest due to their vanishing net magnetic moment and non-relativistic momentum-dependent spin splitting. However, altermagnetic (AM) multiferroics especially triferroics remain scarce. We investigate the experimentally synthesized non-van der Waals CrSb as a model system to explore the effects of dimensionality and facet orientation on its ferroic properties. NiAs, MnP, wurtzite (WZ), zincblende (ZB), and rocksalt (RS) phases are considered. Using first-principles calculations, we predict the altermagnetism of CrSb in MnP phase which has comparable stability with experimental NiAs phase. Both NiAs- and MnP-phase (110) facets exhibit AM-ferroelastic (FC) biferroics, while the WZ-phase bulk and (001) facets host ferromagnetic (FM) or AM-ferroelectric (FE) biferroics. Notably, the WZ-phase (110) facets are identified as FM/AM-FE-FC triferroics, with moderate energy barriers of 0.129 and 0.363 eV atom-1 for FE and FC switching, respectively. Both FE and FC switching can reverse the AM spin splitting in antiferromagnetic (AFM) configurations while preserving the high spin polarization in FM states. The magnetic anisotropy is highly tunable, exhibiting either uniaxial or in-plane behavior depending on the phase, dimension, and facet. This work establishes a framework for designing AM multiferroics through polymorphic, dimensional, and facet engineering, offering promising avenues for multifunctional spintronic applications.
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Soft Condensed Matter

Elucidation of the Correlation between Molecular Conformation and Shear Viscosity of Polymer Melts under Steady-State Shear Flow

Yuhi Sakamaki, Shota Goto, Kang Kim et al. (+1 more)

The rheological behavior of polymer melts is strongly influenced by parameters such as chain length, chain stiffness, and architecture. In particular, shear thinning, characterized by a power-law decrease in shear viscosity with increasing shear rate, has been widely investigated through molecular dynamics simulations. A central question is the connection between molecular conformation under steady flow and the resulting shear-thinning response. In this study, we employ coarse-grained molecular dynamics simulations of linear and ring polymers with varying chain stiffness to examine this relationship, with chain conformations quantified by the gyration tensor. We identified a strong correlation between the velocity-gradient direction component of the gyration tensor and shear viscosity, which exhibits a clear scaling relationship. This indicates that chain extension along the velocity-gradient direction governs the effective frictional force. Notably, this behavior emerges as a general feature, independent of chain architecture and chain stiffness. In addition, shear viscosity was found to correlate with the component of the gyration tensor corresponding to the direction that is not directly influenced by advective effects of shear flow. Because advection is absent in the direction, polymer chains can be regarded as diffusing freely, and the extent of this diffusion appears to be controlled by the shear viscosity.
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All authors Yuhi Sakamaki, Shota Goto, Kang Kim, Nobuyuki Matubayasi

Materials Science

Probing Phase Diagrams of Ordered Two-Dimensional Ice

Bingzheng Wu, Jianming Wu, Sai Duan et al. (+1 more)

Water, a ubiquitous and fundamental substance, plays a critical role across a wide range of disciplines from physics and chemistry to biology and engineering. Despite theoretical predictions of several phases of two-dimensional (2D) ice confined between idealized hydrophobic walls, experimental validation has been limited to the square phase, whose structural origin remains controversial. Here, we propose a realistic nanoconfinement setup using wide-bandgap hexagonal boron nitride (h-BN) as the capping layer and Cu(111) as the substrate. This protocol enables scanning tunneling microscope (STM) to resolve the atomic-scale arrangement of water molecules beneath the h-BN layer, overcoming the limitations of conventional techniques. Simulated STM images unambiguously identify all ordered flat 2D ice phases, as well as coexisting phases, and effectively distinguish them from potential contaminants. These findings establish a robust framework for experiment to systematically probe the phase structures of 2D ice, opening an avenue for studying nanoconfined water under ambient conditions.
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All authors Bingzheng Wu, Jianming Wu, Sai Duan, Xin Xu

Strongly Correlated Electrons

Surface band-selective moiré effect induces flat band in mixed-dimensional heterostructures

Shuming Yu, Zhentao Fu, Dingkun Qin et al. (+11 more)

In this work, we reveal a curious type of moiré effect that selectively modifies the surface states of bulk crystal. We synthesize mixed-dimensional heterostructures consisting of a noble gas monolayer grow on the surface of bulk Bi(111), and determine the electronic structure of the heterostructures using angle-resolved photoemission spectroscopy. We directly observe moiré replicas of the Bi(111) surface states, while the bulk states remain barely changed. Meanwhile, we achieve control over the moiré period in the range of 25 Å to 80 Å by selecting monolayers of different noble gases and adjusting the annealing temperature. At large moiré periods, we observe hybridization between the surface band replicas, which leads to the formation of a correlated flat band. Our results serve as a bridge for understanding the moiré modulation effect from 2D to 3D systems, and provide a feasible approach for the realization of correlated phenomena through the engineering of surface states via moiré effects.
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All authors Shuming Yu, Zhentao Fu, Dingkun Qin, Enting Li, Hao Zhong, Xingzhe Wang, Keming Zhao, Shangkun Mo, Qiang Wan, Yiwei Li, Jie Li, Jianxin Zhong, Hong Ding, Nan Xu

Materials Science

Chromium-doped uranium dioxide fuels: A review

Mack Wesley Cleveland, Andrew Nelson and Ericmoore Jossou

UO2 doped with parts per million Cr2O3 powder is considered a potential near term accident tolerant fuel candidate. Here, the results of decades of industry and academic research into Cr-doped UO2 are analyzed and their shortcomings are critiqued. Focusing on the incorporation mechanisms of Cr into the fuel matrix, we explore a mechanistic understanding of the characteristic properties of Cr-doped UO2, notably, enhanced fission gas retention attributed to enlarged grain sizes following sintering, along with marginal improvements in the thermophysical properties. The findings of recent X-ray Adsorption Near Edge Spectroscopy studies were compared and put into conversation with historic data regarding the incorporation of Cr in UO2. On the basis of defect mechanisms, the case is made for the substitutional incorporation of Cr governing the lattice solubility but not the enhanced U diffusivity. Instead, Cr/Cr2O3 redox chemistry in a well-defined oxygen potential explains the differences in the U diffusivity and O/M ratio. The primary mechanism of doping-enhanced grain growth is found to be liquid assisted sintering due to a CrO(l) eutectic phase at the grain boundaries. The role of inhomogeneities in Cr concentration in UO2 at various length scales across the materials microstructure is highlighted and connected to promising experimental and modeling work to fill in the gaps in the current understanding of Cr-doped UO2. The review ends with an outline of future works that combine meticulous irradiation studies and high resolution experiments with next generation modeling and simulations techniques empowered by machine learning advances to accelerate the fabrication and adoption of Cr-doped UO2 light water reactors.
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Mesoscale and Nanoscale Physics

Thermoelectric Enhancement of Series-Connected Cross-Conjugated Molecular Junctions

Justin P. Bergfield

We investigate the thermoelectric response of single-molecule junctions composed of acyclic cross-conjugated molecules, including dendralene analogues and related iso-poly(diacetylene) (iso-PDA) motifs, in which node-possessing repeat units are connected in series. Using many-body quantum transport theory, we show that increasing the number of repeat units leaves the fundamental gap essentially unchanged while giving rise to a split-node spectrum whose cumulative broadening dramatically enhances the thermopower. This form of quantum enhancement can exceed other interference-based mechanisms, such as the coalescence of nodes into a supernode, suggesting new opportunities for scalable quantum-interference-based materials. Although illustrated here with cross-conjugated systems, the underlying principles apply broadly to series-connected architectures hosting multiple interference nodes. Finally, we evaluate the scaling of the electronic figure of merit ZT and the maximum thermodynamic efficiency. Together, these results highlight the potential for split-node-based materials to realize quantum-enhanced thermoelectric response.
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Superconductivity · Cross-listed from physics.ins-det

Lithographic integration of TES microcalorimeters with SQUID multiplexer circuits for large format spectrometers

Robinjeet Singh, Avirup Roy, Daniel Becker et al. (+12 more)

Arrays of hundreds or thousands of low temperature detectors have been deployed for many experiments, both bolometers for long wavelength applications and calorimeters for shorter wavelength applications. One challenge that is common to many of these arrays is the efficient use of focal plane area to achieve a large fill fraction of absorbers coupled to detectors. We are developing an integrated fabrication of soft X-ray transition edge sensors (TES) and microwave SQUID multiplexers ($\mu$MUX) with the goal of maximizing the fill fraction of the focal plane area on a scale of many thousand pixel detectors. We will utilize lithographically defined high density interconnects to circumvent limitations in existing solutions that use wirebonds or flip-chip bonds. Here we report the first demonstration of combining TES and $\mu$MUX processes into a single TES-System-on-a-Chip (TES-SoC) fabrication on a silicon wafer. The $\mu$MUX SQUIDs and TES electrothermal feedback circuits are microfabricated first and protected with passivating SiO$_2$, then the TES devices and TES-to-SQUID interconnects are fabricated, and finally the protective layer is removed before the fabrication of the microwave resonators. We show that the microwave SQUIDs are functional and have reasonable yield, and that we are able to read out the transition temperature of the connected TESs using those SQUIDs.
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All authors Robinjeet Singh, Avirup Roy, Daniel Becker, Johnathan D. Gard, Mark W. Keller, John A. B. Mates, Kelsey M. Morgan, Nathan J. Ortiz, Daniel R. Schmidt, Daniel S. Swetz, Joel N. Ullom, Leila R. Vale, Michael Vissers, Galen C. O'Neil, Joel C. Weber

Soft Condensed Matter · Cross-listed from physics.comp-ph

A Virtual Fields Method-Genetic Algorithm (VFM-GA) calibration framework for isotropic hyperelastic constitutive models with application to an elastomeric foam material

Zicheng Yan, Jialiang Tao, Christian Franck et al. (+1 more)

This work introduces a calibration framework for material parameter identification in isotropic hyperelastic constitutive models. The framework synergizes the Virtual Fields Method (VFM) to define an objective function with a Genetic Algorithm (GA) as the optimization method to facilitate automated calibration. The formulation of the objective function uses experimental displacement fields measured from Digital Image Correlation (DIC) synchronized with load cell data and can accommodate data from experiments involving homogeneous or inhomogeneous deformation fields. The framework places no restrictions on the target isotropic hyperelastic constitutive model, accommodating models with coupled dependencies on deformation invariants and specialized functional forms with a number of material parameters, and assesses material stability, eliminating sets of material parameters that potentially lead to non-physical behavior for the target hyperelastic constitutive model. To minimize the objective function, a GA is deployed as the optimization tool due to its ability to navigate the intricate landscape of material parameter space. The VFM-GA framework is evaluated by applying it to a hyperelastic constitutive model for compressible elastomeric foams. The evaluation process entails a number of tests that employ both homogeneous and inhomogeneous displacement fields collected from DIC experiments on open-cell foam specimens. The results outperform manual fitting, demonstrating the framework's robust and efficient capability to handle material parameter identification for complex hyperelastic constitutive models.
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All authors Zicheng Yan, Jialiang Tao, Christian Franck, David L. Henann

Mesoscale and Nanoscale Physics

Superconducting meander-line surface coil for NMR spectroscopy of nanoscale thin films

Louis Beaudoin, Aimé Verrier, Youcef A. Bioud et al. (+3 more)

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique to study local magnetism in a variety of materials. However, the inherently low sensitivity of conventional inductively detected solid state NMR typically requires a large number of spins, reducing its applicability to two-dimensional (2D) materials and nanoscale thin films. To overcome this experimental challenge, we introduce a novel probe based on a superconducting meander-line surface coil that significantly enhances the NMR sensitivity for thin samples. Using a NbN meander with an optimized geometry, we demonstrate the sensitivity of this technique by detecting the NMR signal of a 150-nm-thick boron film containing only $\sim 2\times10^{16}$ $^{11}$B nuclear spins. Spin-echo measurements and theoretical modeling offer insight into the parameters limiting the coil's performance. This work lays the foundation for developing highly sensitive NMR probes, potentially unlocking new opportunities for studying atomically thin materials.
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All authors Louis Beaudoin, Aimé Verrier, Youcef A. Bioud, Mathieu Massicotte, Bertrand Reulet, Jeffrey A. Quilliam

Mesoscale and Nanoscale Physics

Low-Temperature Skyrmions and Spiral Reorientation Processes in Chiral Magnets with Cubic Anisotropy: Guidelines for Bridging Theory and Experiment

A. O. Leonov, G. Gödecke, J. Grefe et al. (+2 more)

We revisit the phenomenological Dzyaloshinskii framework, a central theoretical approach for describing magnetization processes in bulk chiral magnets, and demonstrate how magnetocrystalline cubic anisotropy reshapes the phase diagrams of states and provides the key mechanism stabilizing low-temperature skyrmion phases. We show that, for magnetic field directions along the easy anisotropy axes, the phase diagrams feature stable skyrmion pockets for both signs of the anisotropy constant. We further analyze the nature of the transitions at the critical field $H_{c1}$, associated with the reorientation of stable and metastable spirals along the field. We also examine the transition at $H_{c2}$, where the conical state closes into the homogeneous state accompanied by a deviation of the wave vector from the field direction. By mapping characteristic anisotropy-dependent parameters in the theoretical phase diagrams, we provide guidelines for connecting theory with experiment and for estimating the cubic anisotropy constant in Fe$_{1-x}$Co$_x$Si and MnSi. Our results indicate that samples Fe$_{1-x}$Co$_x$Si with small $x \sim 0.1$ possess sufficiently strong cubic anisotropy to stabilize a low-temperature skyrmion phase. Overall, these theoretical findings establish a quantitative framework for predicting and interpreting skyrmion stability in other cubic helimagnets as well.
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All authors A. O. Leonov, G. Gödecke, J. Grefe, S. Süllow, D. Menzel

Wednesday 8 October

Materials Science · Cross-listed from nlin.CD

A Probability Space at Inception of Stochastic Process

Liteng Yang, Yuliang Liu, Jing Liu et al. (+2 more)

Recently, progress has been made in the theory of turbulence, which provides a framework on how a deterministic process changes to a stochastic one owing to the change in thermodynamic states. It is well known that, in the framework of Newtonian mechanics, motions are dissipative; however, when subjected to periodic motion, a system can produce nondissipative motions intermittently and subject to resonance. It is in resonance that turbulence occurs in fluid flow, solid vibration, thermal transport, etc. In this, the findings from these physical systems are analyzed in the framework of statistics with their own probability space to establish their compliance to the stochastic process. In particular, a systematic alignment of the inception of the stochastic process with the signed measure theory, signed probability space, and stochastic process was investigated. It was found that the oscillatory load from the dissipative state excited the system and resulted in a quasi-periodic probability density function with the negative probability regimes. In addition, the vectorial nature of the random velocity splits the probability density function along both the positive and negative axes with slight asymmetricity. By assuming that a deterministic process has a probability of 1, we can express the inception of a stochastic process, and the subsequent benefit is that a dynamic fractal falls on the probability density function. Moreover, we leave some questions of inconsistency between the physical system and the measurement theory for future investigation. We believe that the establishment of the probability density function of resonance nondissipative dynamics in contemporary statistics should make many mathematical tools available and the analytical formulas for the random velocity and probability density function can provide a convenient platform for the development of statistics.
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All authors Liteng Yang, Yuliang Liu, Jing Liu, Hongxuan Li, Wei Chen

Materials Science · Cross-listed from cs.ET

Multi-objective Bayesian Optimization with Human-in-the-Loop for Flexible Neuromorphic Electronics Fabrication

Benius Dunn, Javier Meza-Arroyo, Armi Tiihonen et al. (+2 more)

Neuromorphic computing hardware enables edge computing and can be implemented in flexible electronics for novel applications. Metal oxide materials are promising candidates for fabricating flexible neuromorphic electronics, but suffer from processing constraints due to the incompatibilities between oxides and polymer substrates. In this work, we use photonic curing to fabricate flexible metal-insulator-metal capacitors with solution-processible aluminum oxide dielectric tailored for neuromorphic applications. Because photonic curing outcomes depend on many input parameters, identifying an optimal processing condition through a traditional grid-search approach is unfeasible. Here, we apply multi-objective Bayesian optimization (MOBO) to determine photonic curing conditions that optimize the trade-off between desired electrical properties of large capacitance-frequency dispersion and low leakage current. Furthermore, we develop a human-in-the-loop (HITL) framework for incorporating failed experiments into the MOBO machine learning workflow, demonstrating that this framework accelerates optimization by reducing the number of experimental rounds required. Once optimization is concluded, we analyze different Pareto-optimal conditions to tune the dielectrics properties and provide insight into the importance of different inputs through Shapley Additive exPlanations analysis. The demonstrated framework of combining MOBO with HITL feedback can be adapted to a wide range of multi-objective experimental problems that have interconnected inputs and high experimental failure rates to generate usable results for machine learning models.
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All authors Benius Dunn, Javier Meza-Arroyo, Armi Tiihonen, Mark Lee, Julia W. P. Hsu

Materials Science · Cross-listed from cs.LG

A physics-aware deep learning model for shear band formation around collapsing pores in shocked reactive materials

Xinlun Cheng, Bingzhe Chen, Joseph Choi et al. (+5 more)

Modeling shock-to-detonation phenomena in energetic materials (EMs) requires capturing complex physical processes such as strong shocks, rapid changes in microstructural morphology, and nonlinear dynamics of chemical reaction fronts. These processes participate in energy localization at hotspots, which initiate chemical energy release leading to detonation. This study addresses the formation of hotspots in crystalline EMs subjected to weak-to-moderate shock loading, which, despite its critical relevance to the safe storage and handling of EMs, remains underexplored compared to the well-studied strong shock conditions. To overcome the computational challenges associated with direct numerical simulations, we advance the Physics-Aware Recurrent Convolutional Neural Network (PARCv2), which has been shown to be capable of predicting strong shock responses in EMs. We improved the architecture of PARCv2 to rapidly predict shear localizations and plastic heating, which play important roles in the weak-to-moderate shock regime. PARCv2 is benchmarked against two widely used physics-informed models, namely, Fourier neural operator and neural ordinary differential equation; we demonstrate its superior performance in capturing the spatiotemporal dynamics of shear band formation. While all models exhibit certain failure modes, our findings underscore the importance of domain-specific considerations in developing robust AI-accelerated simulation tools for reactive materials.
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All authors Xinlun Cheng, Bingzhe Chen, Joseph Choi, Yen T. Nguyen, Pradeep Seshadri, Mayank Verma, H. S. Udaykumar, Stephen Baek

Soft Condensed Matter

Unified microscopic theory of equilibrium thermodynamics and ion association in aqueous and non-aqueous electrolytes with explicit hard-core size

Sahin Buyukdagli

Within the framework of a functional integral formalism incorporating ionic charge and hard-core (HC) interactions on an equal footing, we formulate a unified theory of equilibrium thermodynamics and ion association in charged solutions. Via comparison with recent Monte-Carlo (MC) simulation results (J. Forsman et al., PCCP 26, 19921 (2024)), it is shown that our approach is able to predict with quantitative precision the pair distributions of monovalent ions with the typical hydrated sizes d = 3.0 A and 4.0 A up to the molar concentration ni = 2.0 M. Moreover, comparison with additional simulation data from the literature indicates that within the characteristic regime of ionic packing fraction eta <0.1, the formalism can accurately account for the ion size dependence of the excess energy and pressure from d = 14.3 A down to d = 1.6 A. Via the adjustment of the hydration radius, the theory can also reproduce the non-monotonic salt dependence of the experimentally measured osmotic coefficients of various aqueous and non-aqueous solutions. In accordance with AFM experiments involving non-aqueous electrolytes, the underlying sharp competition between the opposite charge attraction and the excluded volume constraint is shown to limit the occurrence of substantial ionic pair formation to the submolar concentration regime ni <50 mM; at larger concentrations, HC repulsion hinders ion association and results in the quasi-saturation of the pair fraction curves.
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Quantum Gases · Cross-listed from quant-ph

Reconfigurable dissipative entanglement between many spin ensembles: from robust quantum sensing to many-body state engineering

Anjun Chu, Mikhail Mamaev, Martin Koppenhöfer et al. (+2 more)

An attractive approach for stabilizing entangled many-body spin states is to employ engineered dissipation. Most existing proposals either target relatively simple collective spin states, or require numerous independent and complex dissipative processes. Here, we show a surprisingly versatile scheme for many-body reservoir engineering that relies solely on fully collective single-excitation decay, augmented with local Hamiltonian terms. Crucially, all these ingredients are readily available in cavity QED setups. Our method is based on splitting the spin system into groups of sub-ensembles, and provides an easily tunable setup for stabilizing a broad family of pure, highly entangled states with closed-form analytic descriptions. Our results have immediate application to multi-ensemble quantum metrology, enabling Heisenberg-limited sensing of field gradients and curvatures. Notably, our approach solves an important challenge in differential quantum sensing by providing the first example of Heisenberg-limited differential sensing immune to common-mode noise and accessible with only simple one-body measurements. The same setup also allows the stabilization of an entire family of entangled states in a 1D chain of spin ensembles with symmetry-protected topological (SPT) order, and have a direct connection to the outputs of sequential unitary circuits. A special case of our protocol efficiently stabilizes the celebrated Affleck-Kennedy-Lieb-Tasaki (AKLT) state.
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All authors Anjun Chu, Mikhail Mamaev, Martin Koppenhöfer, Ming Yuan, Aashish A. Clerk

Materials Science · Cross-listed from physics.optics

Observation of Crystalline Nonlocal Volume Plasmon Waves

Sathwik Bharadwaj, Makoto Schreiber, Jungho Mun et al. (+6 more)

In plasmonics, nonlocal effects arise when the material response to optical excitations is strongly dependent on the spatial correlations of the excitation. It is well known that a classical free electron gas system supports local Drude volume plasmon waves. Whereas a compressible quantum electron gas system sustains hydrodynamic volume plasmons with nonlocal dispersion isotropic across all high-symmetry directions. Here, distinct from Drude and Hydrodynamic plasmon waves, we present the first observation of crystalline nonlocal volume plasmon waves. We use transmission-based momentum-resolved electron energy loss spectroscopy to measure the volume plasmon dispersion of silicon along all the fundamental symmetry axes, up to high momentum values ($q \sim 0.7$ reciprocal lattice units). We show that crystalline nonlocal plasmon waves have a prominent anisotropic dispersion with higher curvature along the light-mass ($\Gamma K$ & $\Gamma L$) axes, compared to the heavy-mass ($\Gamma X$) axis. We unveil the origin of this phenomenon by experimentally extracting the anisotropic Fermi velocities of silicon. Our work highlights an exquisite nonlocality-induced anisotropy of volume plasmon waves, providing pathways for probing many-body quantum effects at extreme momenta.
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All authors Sathwik Bharadwaj, Makoto Schreiber, Jungho Mun, Sam Ruttiman, Pronoy Das, Misa Hayashida, Marek Malac, Peter Nordlander, Zubin Jacob

Soft Condensed Matter

Magnetically Responsive Microprintable Soft Nanocomposites with Tunable Nanoparticle Loading

Rachel M. Sun, Andrew Y. Chen, Yiming Ji et al. (+3 more)

Magnetic remote actuation of soft materials is attractive for applications such as transforming materials and medical robots. However, due to manufacturing limitations, microscale magnetoactive devices are scarce – light-based additive manufacturing methods, despite achieving microscale resolution, struggle with particle-induced light scattering. Moreover, large hard-magnetic microparticles restrict ultimate feature sizes, and deformation of soft-magnetic nanoparticle composites requires impractically high loading and field gradients. Among successfully fabricated microscale soft-magnetic composites, limited control over particle loading, distribution, and matrix-phase stiffness has hindered their functionality. Here, we combine two-photon polymerization with iron oxide nanoparticle coprecipitation to fabricate 3D-printed microscale nanocomposites with spatially tunable nanoparticle distribution. We control nanoparticle content by locally modulating the two-photon dose, imbuing parts with varied magnetic functionality and achieving millimeter-scale elastic deformations, demonstrated by a soft robotic gripper and a bistable bit register and sensor. Our approach enables precise control of mechanical and magnetic properties towards microscale metamaterial and robotics applications.
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All authors Rachel M. Sun, Andrew Y. Chen, Yiming Ji, Eric M. Stewart, Daryl W. Yee, Carlos M. Portela

Materials Science

Magnetotransport in Topological Materials and Nonlinear Hall Effect via First-Principles Electronic Interactions and Band Topology

Dhruv C. Desai, Lauren A. Tan, Jin-Jian Zhou et al. (+3 more)

Topological effects arising from the Berry curvature lead to intriguing transport signatures in quantum materials. Two such phenomena are the chiral anomaly and nonlinear Hall effect (NLHE). A unified description of these transport regimes requires a quantitative treatment of both band topology and electron scattering. Here, we show accurate predictions of the magnetoresistance in topological semimetals and NLHE in noncentrosymmetric materials by solving the Boltzmann transport equation (BTE) with electron-phonon ($e$-ph) scattering and Berry curvature computed from first principles. We apply our method to study magnetotransport in a prototypical Weyl semimetal, TaAs, and the NLHE in strained monolayer WSe$_2$, bilayer WTe$_2$ and bulk BaMnSb$_2$. In TaAs, we find a chiral contribution to the magnetoconductance which is positive and increases with magnetic field, consistent with experiments. We show that $e$-ph interactions can significantly modify the Berry curvature dipole and its dependence on temperature and Fermi level, highlighting the interplay of band topology and electronic interactions in nonlinear transport. The computed nonlinear Hall response in BaMnSb$_2$ is in agreement with experiments. By adding the Berry curvature to first-principles transport calculations, our work advances the quantitative analysis of a wide range of linear and nonlinear transport phenomena in quantum materials.
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All authors Dhruv C. Desai, Lauren A. Tan, Jin-Jian Zhou, Shiyu Peng, Jinsoo Park, Marco Bernardi

Strongly Correlated Electrons

Quantizing Bosonized Fermi Surfaces

Sihan Chen and Luca V. Delacretaz

Bosonization describes Fermi surface dynamics in terms of a collective field that lives on a part of phase space. While sensible semiclassically, the challenge of treating such a field quantum mechanically has prevented bosonization from providing as powerful a nonperturbative tool as in one dimension. We show that general Fermi surfaces can be exactly described by a particular $N\to \infty$ limit of a $U(N)_1$ WZW model, with a tower of irrelevant corrections. This matrix-valued description encodes the noncommutative nature of phase space, and its (solvable) strongly coupled dynamics resolves the naive overcounting of degrees of freedom of the collective field without the need to cut the Fermi surface into patches. This approach furthermore provides a quantitative tool to systematically study power-law corrections to Fermi surface dynamics.
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Mesoscale and Nanoscale Physics

Controlling the Spin-Wave Nonreciprocity of a Crescent-Shaped Nanowire via Curvature and Magnetic Field

Uladzislau Makartsou, Mateusz Gołębiewski, Attila Kákay et al. (+2 more)

Recent studies on spin-wave propagation in ferromagnetic waveguides has highlighted the role of nonreciprocity resulting from the chiral nature of dipolar interactions in curved elements. However, the impact of spin-wave mode type on nonreciprocity remains unexplored. Using micromagnetic simulations supported by analytical modeling, we systematically analyzed the propagation of edge, fundamental, and width-quantized spin-wave modes in a ferromagnetic nanowire with a crescent-shaped cross-section. Our results show that the strength and sign of nonreciprocity depend on the mode type, as well as on the curvature magnitude of the nanowire's top and bottom surfaces and the strength of the external magnetic field. Interestingly, changing the mode type, for instance induced by altering the curvature or magnetic field, result in a significant change in the dispersion relation asymmetry. This effect underscores the important role of spin-wave profiles in nonreciprocity, deepens our fundamental understanding of spin-wave dynamics in curved geometries, and paves the way for designing magnonic waveguides with tailored properties.
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All authors Uladzislau Makartsou, Mateusz Gołębiewski, Attila Kákay, Olena Tartakivska, Maciej Krawczyk

Statistical Mechanics

What is the most optimal diffusion?

Vasili Baranau

What is the fastest possible "diffusion"? A trivial answer would be "a process that converts a Dirac delta-function into a uniform distribution infinitely fast". Below, we consider a more reasonable formulation: a process that maximizes differential entropy of a probability density function (pdf) $f(\vec{x}, t)$ at every time $t$, under certain restrictions. Specifically, we focus on a case when the rate of the Kullback-Leibler divergence $D_{\text{KL}}$ is fixed. If $\Delta(\vec{x}, t, d{t}) = \frac{\partial f}{ \partial t} d{t}$ is the pdf change at a time step $d{t}$, we maximize the differential entropy $H[f + \Delta]$ under the restriction $D_{\text{KL}}(f + \Delta || f) = A^2 d{t}^2$, $A = \text{const} > 0$. It leads to the following equation: $\frac{\partial f}{ \partial t} = - \kappa f (\ln{f} - \int f \ln{f} d{\vec{x}})$, with $\kappa = \frac{A}{\sqrt{ \int f \ln^2{f} d{\vec{x}} - \left( \int f \ln{f} d{\vec{x}} \right)^2 } }$. Notably, this is a non-local equation, so the process is different from the Itô diffusion and a corresponding Fokker-Planck equation. We show that the normal and exponential distributions are solutions to this equation, on $(-\infty; \infty)$ and $[0; \infty)$, respectively, both with $\text{variance} \sim e^{2 A t}$, i.e. diffusion is highly anomalous. We numerically demonstrate for sigmoid-like functions on a segment that the entropy change rate $\frac{d H}{d t}$ produced by such an optimal "diffusion" is, as expected, higher than produced by the "classical" diffusion.
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Soft Condensed Matter

Anomalous proteinaceous shells with octagonal local order

Sergei B. Rochal, Aleksey S. Roshal, Olga V. Konevtsova et al. (+1 more)

Proteinaceous shells useful for various biomedical applications exhibit a wide range of anomalous structures that are fundamentally different from icosahedral viral capsids described by the Caspar-Klug paradigmatic model. Exploring the Protein Data Bank, we have identified nine different types of anomalous shells structurally close to flat octagonal quasicrystals. As we show, these numerous shells have cubic nets cut from short-period approximants of an octagonal tiling composed of square and rhombic tiles. The approximants and parent tiling are easily obtained within the Landau density wave approach, while the nonequilibrium assembly of them can be simulated using the pair potentials derived from critical density waves. Gluing a polyhedron net and mapping it onto a spherical surface induces tile distortions, and to reduce them, we introduce and minimize the effective elastic energy of the system. Thus, we return quasi-equivalence to previously equivalent tiles. Possible cubic faceting of the octagonal spherical tilings is discussed in terms of the topological charge distribution over the tiling vertices. The proposed structural models describe numerous proteinaceous shells including about half of the known symmetrical enzymes. Our results constitute a fundamental basis for further applications of identified octagonal assemblies and can help to discover and study similar systems in the future.
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All authors Sergei B. Rochal, Aleksey S. Roshal, Olga V. Konevtsova, Rudolf Podgornik

Statistical Mechanics

Thermodynamically Consistent Continuum Theory of Magnetic Particles in High-Gradient Fields

Marko Tesanovic, Daniel M. Markiewitz, Marcus L. Popp et al. (+2 more)

Magnetic particles underpin a broad range of technologies, from water purification and mineral processing to bioseparations and targeted drug delivery. The dynamics of magnetic particles in high-gradient magnetic fields-encompassing both their transport and eventual capture-arise from the coupled interplay of field-driven drift, fluid advection, and particle-field feedback. These processes remain poorly captured by existing models relying on empirical closures or discrete particle tracking. Here, we present a thermodynamically consistent continuum theory for collective magnetic particle transport and capture in high-gradient fields. The framework derives from a free-energy functional that couples magnetic energy, entropic mixing, and steric interactions, yielding a concentration-dependent susceptibility via homogenization theory. The resulting equations unify magnetism, mass transport, and momentum balances without ad hoc shut-off criteria, allowing field shielding, anisotropic deposition, and boundary-layer confinement to emerge naturally. Simulations predict canonical capture morphologies-axially aligned plumes, crescent-shaped deposits, and nonlinear shielding-across field strengths and flow regimes, consistent with trends reported in prior experimental and modeling studies. By organizing captured particle mass data into a dimensionless phase diagram based on the Mason number, we reveal three distinct regimes-thermodynamically controlled, transitional, and dynamically controlled. This perspective provides a predictive platform for in silico optimization and extension to three-dimensional geometries, and informing digital twin development for industrial-scale high-gradient magnetic separation processes.
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All authors Marko Tesanovic, Daniel M. Markiewitz, Marcus L. Popp, Martin Z. Bazant, Sonja Berensmeier

Superconductivity

Efficiency of the superconducting diode effect of pair-density-wave states in two-dimensional $d$-wave altermagnets

Igor de M. Froldi and Hermann Freire

We systematically study the efficiency of the intrinsic superconducting diode effect of several pair-density-wave states that can emerge in two-dimensional $d$-wave metallic altermagnets. To this end, we investigate several scenarios using an effective minimal microscopic model and Ginzburg-Landau analysis in order to derive the corresponding pairing phase diagrams. In addition, we examine also whether the presence of a Rashba spin-orbit coupling and an applied external magnetic field are beneficial to this effect in these systems. As a consequence, our results add further support to the fact that altermagnetic materials indeed provide a good platform for the pursuit of finite-momentum superconductivity, which can lead to an optimization of the diode efficiency in some physically interesting situations. The latter phenomenon has been recently proposed to be key in improving the applicability of new energy-efficient quantum electronic devices.
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Quantum Gases

Dissipative Generation of Currents by Nonreciprocal Local and Global Environments

Catalin-Mihai Halati

We investigate the mechanisms necessary for the stabilization of complex quantum correlations by exploring dissipative couplings to nonreciprocal reservoirs. We analyze the role of locality in the coupling between the environment and the quantum system of interest, as we consider either local couplings throughout the system, or a single global coupling. We contrast the results obtained for the two scenarios in which a chain of strongly interacting hardcore bosonic atoms is coupled directly to Markovian kinetic dissipative processes, or experiences effective dissipation through the mediation of the field of a lossy optical cavity. To investigate the dissipative dynamics of the many-body quantum systems considered we perform numerical simulations employing matrix product states methods. We show that by coupling atomic tunneling terms to the global field of a dissipative cavity we can stabilize at long times both finite currents and current-current correlations throughout the atomic chain. This is in contrast to the setup in which dissipation acts directly via local tunneling processes, where currents arise in a narrow region of the system and the current-current correlations are rapidly decaying.
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Materials Science

Ultrathin bismuth-yttrium iron garnet films with tunable magnetic anisotropy

Hanchen Wang, William Legrand, Davit Petrosyan et al. (+7 more)

We report on the epitaxial growth of nm-thick films of bismuth-substituted yttrium iron garnet (BiYIG) by high-temperature off-axis radio-frequency magnetron sputtering. We demonstrate accurate control of the magnetic properties by tuning of the sputtering parameters and epitaxial strain on various (111)-oriented garnet substrates. BiYIG films with up to -0.80% lattice mismatch with the substrate remain fully strained up to 60~nm-thick, maintaining a high crystalline quality. Transmission electron microscopy and energy-dispersive X-ray spectroscopy confirm coherent epitaxial growth, the absence of defects, and limited interdiffusion at the BiYIG/substrate interface. Varying the tensile or compressive strain between -0.80% and +0.56% in BiYIG allows for accurate compensation of the total magnetic anisotropy through magneto-elastic coupling. The effective magnetic anisotropy of sputtered BiYIG films can be further tuned via the off-axis deposition angle and the oxygen flow during growth, which determine the cation stoichiometry. Under optimized growth conditions, a ferromagnetic resonance (FMR) linewidth of 1~mT at 10~GHz is reliably obtained even for thicknesses as low as 10~nm. We also report small FMR linewidths in ultrathin (2-5~nm) BiYIG films grown on diamagnetic substrate yttrium scandium gallium garnet. These findings highlight the promise of low-damping, strain-engineered nm-thick BiYIG films for implementing advanced functionalities in spin-orbitronic and magnonic devices. Specifically, the magnetic-anisotropy compensation and low damping enable large cone-angle magnetization dynamics immune to magnon-magnon nonlinear scattering.
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All authors Hanchen Wang, William Legrand, Davit Petrosyan, Min-Gu Kang, Emir Karadža, Hiroki Matsumoto, Richard Schlitz, Michaela Lammel, Myriam H. Aguirre, Pietro Gambardella