Mesoscale and Nanoscale Physics
Magnon polaritons in a van der Waals ferromagnet coupled to a superconducting resonator
Alvaro Bermejillo-Seco, Luuk J. van der Goot, Matteo Arfini et al. (+3 more)
Achieving
magnon-
photon hybridization in the microwave regime is essential for integrating
magnetic excitations with superconducting
circuits. While this has been extensively demonstrated in bulk
magnetic systems, realizing it in two-dimensional van der Waals materials remains challenging due to their reduced
magnetic volume and increased dissipation. Here,
magnon-
photon hybridization is observed in exfoliated flakes of the van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$, with thicknesses down to 30 nm. The resulting
magnon polaritons-hybrid excitations of cavity
photons and
magnons-are evidenced by reproducible avoided crossings across six devices, enabled by a low-impedance superconducting resonator design. The coupling strength follows the expected square-root dependence on thickness, and extrapolation of this scaling indicates that hybridization in the monolayer limit is within reach.
Read the full abstract ▾
All authors Alvaro Bermejillo-Seco, Luuk J. van der Goot, Matteo Arfini, Yaroslav M. Blanter, Gary A. Steele, Herre S.J. van der Zant
Superconductivity
Phase-slip residual-order spin state in FeSe
Zhixin Liu, Jiyu Fan, Lei Zhang et al. (+3 more)
In unconventional
superconductors, the microscopic form of
magnetic correlations is crucial for identifying the origin of
spin fluctuations and the associated pairing interaction. FeSe superconducts without chemical doping and shows no static long-range
magnetic order, yet inelastic
neutron scattering reveals a strong stripe response, finite linewidths, and reproducible Neel-side spectral weight. Here we propose a phase-slip residual-order
spin state (ROSS). Stripe, Neel, pair-checkerboard, and staggered trimer
antiferromagnetic states can be unified as symmetric phase-slip derivatives of a stripe background, while more general asymmetric phase slips form lower-energy configurations and reconstruct the
spin structure factor S(q) within a finite coherence length. The ROSS therefore reconciles the absence of static
magnetic order with strong
spin excitations, provides a microscopic picture for the origin of
spin fluctuations in FeSe, and establishes a
magnetic basis for understanding pairing in unconventional superconducting systems with similar
magnetic fingerprints.
Read the full abstract ▾
All authors Zhixin Liu, Jiyu Fan, Lei Zhang, Ma Chunlan, Zhongqin Yang, Yan Zhu
Materials Science
Decoupling size from magnetism: A length-scale boundary for curvature control in micrometer FePt Janus particles
Natalia Gonzalez-Vazquez, Eylül Suadiye, Eberhard Goering et al. (+6 more)
Curvature reshapes magnetization when a structure's dimensions approach intrinsic
magnetic length scales, but functional
magnetic colloids and microrobots are often micrometers in size, where the radius of
curvature exceeds these scales by several orders of magnitude. Whether particle diameter remains an effective parameter for tuning
magnetic response in this regime is therefore unclear. We synthesized partially ordered FePt Janus caps on spherical SiO$_2$ particles with diameters of 3–10~$\mu$m, characterized their structure and
magnetic response, and extended the investigated range to 1–20~$\mu$m using micromagnetic simulations. Across this range, coercivity, remanence, and hysteresis-loop shape showed no systematic dependence on particle diameter in either experiment or simulation. The ratio between exchange length and radius of
curvature ($\ell_{\mathrm{ex}}/R \sim 10^{-3}$–$10^{-4}$) places these particles in a locally planar regime where diameter-dependent
curvature effects are weak. Size and
magnetic response are therefore effectively decoupled within the investigated regime: particle diameter can be selected according to transport, payload, and biocompatibility requirements without introducing a measurable
magnetic penalty, but it does not provide an effective route for tuning magnetization reversal. Instead, the
magnetic response is governed primarily by material state, including the balance between magnetically hard L1$_0$ and soft A1 FePt, with additional modulation by processing-induced morphology. The resulting length-scale map identifies the regime in which this decoupling is expected to hold and where diameter-dependent
curvature effects may become significant.
Read the full abstract ▾
All authors Natalia Gonzalez-Vazquez, Eylül Suadiye, Eberhard Goering, Ruben O. Miranda-Rosales, Hilda David, Frank Thiele, Julia Unangst, Andrew K. Schulz, Gunther Richter
Mesoscale and Nanoscale Physics
Probing charge noise in bilayer graphene quantum dots by Landau-Zener-Stückelberg-Majorana spectroscopy
Katrin Hecker, Samuel Möller, Tobias Deußen et al. (+6 more)
Charge noise is an important factor limiting
qubit coherence and relaxation in solid-state devices. In
bilayer graphene (BLG)
quantum dots, recently established as a promising platform for
spin- and valley-based
qubits, both the origin and magnitude of charge noise remain largely unexplored. Here, we investigate high-frequency charge noise using Landau-Zener-Stückelberg-Majorana (LZSM) interference spectroscopy. We study a single-particle charge
qubit formed in a BLG double
quantum dot at frequencies between 5 and 10 GHz and extract a noise spectral density $S_\varepsilon$ on the order of 0.5-0.9 neV$/\sqrt{\mathrm{Hz}}$. This is comparable to values reported for III-V
semiconductor platforms and silicon. From the temperature and frequency dependence of the charge
qubit decoherence, we conclude that thermal (Johnson) noise or electron-
phonon coupling dominates over two-level fluctuators.
Read the full abstract ▾
All authors Katrin Hecker, Samuel Möller, Tobias Deußen, Hubert Dulisch, Luca Banszerus, Kenji Watanabe, Takashi Taniguchi, Christian Volk, Christoph Stampfer
Materials Science
Engineering the band structure of few-layer graphene by S-doping: from linear dispersion to impurity flat bands
Armin Sahinovic and Rossitza Pentcheva
Motivated by the technological relevance of S-doped few-layer
graphene (FLG) in battery applications and in the oxygen reduction reaction, we systematically explore the effect of basal plane S-doping on the electronic properties of mono-, bi-, and four-layer
graphene, using first-principles calculations with van der Waals corrections. In the monolayer we find a variety of effects ranging from a sustained Dirac cone with localized
impurity bands away from the
Fermi level for thiophenic doping (2V1S) to a band gap opening of 0.4 eV and
impurity flat bands close to the
Fermi-level for graphitic doping (1V1S) and an additional $n$-type doping together with
spin-polarization for thiopyranic doping (4V3S). Incorporation in FLG leads to modification of the Dirac cone into a set of
hyperbolic touching bands in 2V1S; reduction (
bilayer) and closing of the band gap with additional
hyperbolic touching bands in conjunction with an
impurity flat band at the
Fermi level in 1V1S and 4V3S and a reduction of
spin polarization in the latter. Overall, S-doping enables design of the band structure and tuning the electronic behavior of FLG from metallic to insulating and from linear dispersion to
impurity flat bands that makes S-doped FLG a promising material for versatile technological applications.
Read the full abstract ▾
Statistical Mechanics · Cross-listed from hep-ph
Toward Charge-Dependent Tests of the Equivalence Principle: A Phenomenological Parameter and an Unexplored Frontier
Renato Vieira dos Santos
We introduce and define the phenomenological parameter $\kappa$, defined by $\Delta a/g = \kappa \, \Delta(q/m)$, to quantify potential linear coupling between electric charge and gravitational acceleration. A synthesis of existing precision equivalence principle experiments yields the first quantitative estimate of the effective sensitivity to this coupling: $|\kappa| < 2.1 \times 10^{-4}$ kg/C at 95% confidence level. This constraint is approximately eleven orders of magnitude less stringent than corresponding bounds on composition-dependent violations, revealing that the electromagnetic axis remains a largely underexplored frontier in empirical
gravity. We connect $\kappa$ to established frameworks – the Standard-Model Extension and the $TH\epsilon\mu$ formalism – showing that it occupies a region of parameter space untouched by existing high-precision tests. An effective field theory analysis shows that dimension-six operators that couple
curvature directly to the electromagnetic field strength are suppressed by the minuscule terrestrial spacetime
curvature ($G_N \rho_\oplus \sim 10^{-55}~\text{GeV}^2$) and are therefore phenomenologically irrelevant. Consequently, a future measurement of $\kappa$ at an accessible level would not probe minimal
geometric couplings but would signal physics beyond minimal gravitational EFT, such as mediation by light scalar fields as in Einstein-Maxwell-Dilaton theory. We examine the Schiff-Barnhill effect, the primary systematic background for any such measurement, and show how it can be separated from a genuine signal. We outline the necessary experimental strategy, focused on maximizing charge-to-mass ratio differences, to transform this overlooked axis into a targeted probe for new physics.
Read the full abstract ▾
Materials Science
Probing Non-Equilibrium Grain Boundary Dynamics with XPCS and Domain-Adaptive Machine Learning
Mouyang Cheng, Bowen Yu, Chu-Liang Fu et al. (+14 more)
Grain-boundary (GB) dynamics control the stability, mechanical, and functional response of nanocrystalline materials, but direct experimental access to their slow non-
equilibrium motion has been limited. Here we establish X-ray
photon correlation spectroscopy (XPCS), combined with domain-adaptive machine learning, as a quantitative probe of GB dynamics. Temperature- and grain-size-dependent two-time XPCS measurements in nanocrystalline silicon reveal pronounced departures from time-translation invariance, showing that GB relaxation can remain far from
equilibrium over experimental timescales. However, direct extraction of quantitative physical information from these high-dimensional, noisy fluctuation maps faces a significant challenge. To overcome this barrier, we develop a semi-supervised learning framework that transfers physical parameter labels from continuum simulations to unlabeled experimental XPCS maps through domain-adaptive representation
alignment. This AI-augmented approach enables the extraction of key kinetic parameters, including bulk diffusivity, GB stiffness, and effective GB concentration, directly from experimental XPCS measurements. Our results show how machine learning can transform indirect fluctuation signals into quantitative materials dynamics, providing a general route to study non-
equilibrium defect motion in solids.
Read the full abstract ▾
All authors Mouyang Cheng, Bowen Yu, Chu-Liang Fu, Nina Andrejevic, Matthias T. Agne, Riley Hanus, Qiwei Wan, Nathan C. Drucker, Thanh Nguyen, Andrei Fluerasu, Lutz Wiegart, Xiaoqian M Chen, Daniel Pajerowski, Yongqiang Cheng, Joshua J Turner, G. Jeffrey Snyder, Mingda Li
Strongly Correlated Electrons · Cross-listed from math-ph
Local Topological Quantum Order and Spectral Gap Stability for the AKLT Models on the Hexagonal and Lieb Lattices
Thomas Jackson, Bruno Nachtergaele and Amanda Young
We prove that the ground state of the AKLT models on the hexagonal
lattice and the Lieb
lattice satisfy the local topological
quantum order (LTQO) condition. This will be a consequence of proving that the finite volume ground states are indistinguishable from a unique infinite volume ground state. Concretely, we identify a sequence of increasing and absorbing finite volumes for which any finite volume ground state expectation is well approximated by the infinite volume state with error decaying at a uniform exponential rate in the distance between the support of the observable and boundary of the finite volume. As a corollary to the LTQO property, we obtain that the spectral gap above the ground state in these models is stable under general small perturbations of sufficient decay. We prove these results by a detailed analysis of the
polymer representation of the ground states state derived by Kennedy, Lieb and Tasaki (1988) with the necessary modifications required for proving the strong form of ground state indistinguishability needed for LTQO.
Read the full abstract ▾
Soft Condensed Matter
Morphology-resolved stress contributions in sheared wet granular materials
Ahmad Awdi, Camille Chateau, Coumba Niang et al. (+3 more)
Three-dimensional X-ray microtomography, coupled to rheometric measurements, enables a morphology-resolved reconstruction of capillary stresses at the grain scale in unsaturated wet granular materials.
Liquid domains are automatically classified into capillary bridges, dimers, trimers, and larger clusters, and their spatial organization is tracked as a function of shear deformation and
liquid content. We show that shear localization governs the redistribution of the
liquid phase: capillary bridges remain uniformly distributed throughout the sample, while higher-order morphologies accumulate preferentially near the lower boundary of the shear-zone through a shear-driven coalescence mechanism. Despite this spatial localization, simple two-grain bridges generate the dominant contribution to the isotropic capillary pressure, accounting for nearly 85% of the total at
liquid-to-solid volume ratio $\epsilon = 0.05$, whereas more complex
liquid clusters contribute only weakly to the overall cohesion. Incorporating the morphology-resolved capillary pressure into an effective-stress framework qualitatively reproduces the macroscopic friction coefficient across the full range of investigated
liquid contents, without adjustable parameters. These results establish a predictive micro–macro link between
liquid morphology and the rheology of wet granular materials.
Read the full abstract ▾
All authors Ahmad Awdi, Camille Chateau, Coumba Niang, Patrick Aimedieu, Jean-Noël Roux, Abdoulaye Fall
Mesoscale and Nanoscale Physics
Flow bistability in non-Newtonian electron fluid
A. N. Afanasiev and P. S. Alekseev
Modern two dimensional conductors with low defect densities and strong electron-electron scattering are favorable platforms for formation of a viscous fluid of conduction electrons. Electric properties of these systems are determined by the hydrodynamic regime of charge transport distinguished by many experimental signatures: a decrease in sample resistance with increasing temperature (the Ghurzhi effect), strong negative magnetoresistance and others. Here we consider the flow of 2D electron fluid in the nonlinear regime characterized by non-Newtonian viscosity which depends on spatial gradients of hydrodynamic velocity. We derive a simplified version of the dynamic equations for the non-Newtonian electron fluid and consider the specific underlying mechanism associated with local electron heating. Recent works have demonstrated that this may be one of the main mechanisms for nonlinearity in 2D electron fluids. We show that in a certain range of parameters, the two steady-state flow configurations coexist for the narrow channel geometry, and this bistability leads to an S-shaped current-voltage characteristic. By solving the derived time-dependent dynamic equations, we trace the transient response to a step variation of the longitudinal voltage and demonstrate how the current switching and hysteresis occur in samples with the non-Newtonian electron fluid.
Read the full abstract ▾
Materials Science · Cross-listed from quant-ph
Understanding oxide-thickness-dependent variability in dense Si-MOS quantum dot arrays
Arne Loenders, Jacques Van Damme, Clement Godfrin et al. (+19 more)
Achieving uniform and scalable control of
semiconductor spin qubits remains a key challenge for large scale
quantum computing. In this work, we investigate how gate
oxide thickness influences uniformity in dense two dimensional silicon
quantum dot arrays. Using a 7 x 7 array fabricated in a 300 mm CMOS-process patterned by EUV lithography, we statistically characterize 392
quantum dots across four different
oxide thicknesses. The threshold voltages, capacitances, lever arms, and charging energies are extracted using parallel row based measurements and we identify an optimal SiO2 thickness of 17 nm that minimizes threshold voltage variability below 63 mV standard deviation. Our observations illustrate how multiple sources of disorder can introduce competing
oxide-thickness dependencies, resulting in non-monotonic trends. These results provide key design guidelines for dense, scalable silicon
spin qubit architectures.
Read the full abstract ▾
All authors Arne Loenders, Jacques Van Damme, Clement Godfrin, Paola Favia, Jacopo Franco, Thomas Van Caekenberghe, Bart Raes, Gulzat Jaliel, Sylvain Baudot, Luis Francisco Pinotti, Alexander Grill, George Simion, Kristof Moors, Vukan Levajac, Sofie Beyne, Sugandha Sharma, Stefan Kubicek, Yosuke Shimura, Roger Loo, Massimo Mongillo, Danny Wan, Kristiaan De Greve
Statistical Mechanics
Identifying the relevant parameters in design strategies for stable glasses
Leonardo Galliano and Ludovic Berthier
A glass is conventionally obtained by cooling a bulk supercooled
liquid through its glass transition temperature. The discovery of ultrastable glasses prepared using physical vapor deposition, together with the recent multiplication of numerical
algorithms created to increase the stability of glasses, demonstrates the existence of a variety of strategies for designing glasses with different physical properties. This raises a broader question: which parameters most strongly govern the enhancement of glass stability? Existing computational strategies often produce highly stable glasses by optimizing certain physical properties through dynamical changes in particle diameters. We challenge the idea that these physical quantities are causally responsible for glass stability and suggest instead that diameter dynamics is the principal source of enhanced stability. To support our view, we introduce computational methods to optimize physical quantities without changing the particle diameters. Using the examples of enhanced hyperuniformity at large scale and local ordering at small scale, we design glass configurations with highly optimized values compared to bulk
equilibrium states. However, these glasses do not show enhanced stability. The proposed physical quantities are correlated with glass stability, but are not causally responsible for ultrastability. These findings indicate that design rules for stable glasses should be reinterpreted in terms of the dynamical processes that generate stability, rather than the optimized physical quantities they target.
Read the full abstract ▾
Soft Condensed Matter
Following the thread: surface and bulk solvent migration in silicone elastomers from local volumetric swelling
Chenzhuo Li, Tom Beyeler, Marc Antonio Chalhoub et al. (+1 more)
Poroelastic materials, consisting of a permeable solid
matrix infiltrated with fluid, are ubiquitous in natural and engineering contexts. In poroelastic
polymer solids, the elastic
matrix swells to
equilibrium when immersed in a solvent bath; thus, the network elasticity couples to the solvent transport. Despite the ubiquity and importance of poroelastic theory in describing phenomena as diverse as earthquakes and biological tissues, there is a paucity of experimental data that probe the local network response to controlled stress and solvent boundary conditions. Here, we first probe the baseline
diffusion kinetics of a polymeric solvent during free swelling of a polydimethylsiloxane (PDMS) network with well-characterized silicone oils. In situ 3D spatiotemporal measurements identify a flux-limited interfacial boundary condition, contradicting the canonical fully drained assumption. This correction eliminates an order-of-magnitude underestimation of diffusivity in standard bulk analysis. The swelling
equilibrium is accurately captured by a Flory-Rehner theory that requires modification to include the effective finite extensibility of the filled network. Solvent migration is then studied using a bending configuration for three material preparations: as-prepared, mobile-phase-free, and fully swollen in silicone oils. The as-prepared and mobile-phase-free beams show no discernible volumetric change or force relaxation, whereas local in situ measurements directly resolve tensile-side dilation and compressive-side contraction, yielding the effective diffusivities in agreement with the force-relaxation data. These measurements rigorously
benchmark solvent diffusivity in
polymer networks, underscoring the importance of unambiguous interfacial boundary conditions and shedding light on mechanics and engineering across poroelastic
polymers and geomaterials.
Read the full abstract ▾
All authors Chenzhuo Li, Tom Beyeler, Marc Antonio Chalhoub, John M. Kolinski
Statistical Mechanics · Cross-listed from quant-ph
Squeezing and adiabaticity breaking in time-dependent quantum harmonic oscillators
Mattia Orlandini, Beatrice Donelli, Lorenzo Buffoni et al. (+1 more)
The
quantum harmonic oscillator with time-dependent frequency is a paradigmatic model of driven
quantum dynamics and one of the few nontrivial systems that admits an exact analytical solution. In this review paper, we present a unified treatment of the time-dependent oscillator based on the Lewis-Riesenfeld invariant method, Bogoliubov transformations and the Ermakov-Pinney equation. We show how these approaches naturally connect to squeezing for the description of excitations production, and to the breakdown of adiabaticity under generic frequency protocols. Exact results for sudden quenches and smooth ramps are discussed in detail. By explicitly bridging invariant methods and squeezing formalism, this review is meant to provide a comprehensive framework for understanding nonequilibrium dynamics in quadratic potentials, with applications ranging from thermodynamics and condensed matter to
quantum control theory.
Read the full abstract ▾
All authors Mattia Orlandini, Beatrice Donelli, Lorenzo Buffoni, Stefano Gherardini
Soft Condensed Matter
Cell divisions suppress dynamical correlations in solid tissues
Ali Tahaei, Ahandeep Manna and Marko Popović
Developing tissues often maintain mechanical coherence while continuously remodeling through cellular processes such as
cell divisions and rearrangements. In this way, they are an example of amorphous solids. In passive amorphous solids, local rearrangements can trigger one another through long-ranged elastic interactions, leading to system-spanning avalanches near yielding. Whether similar collective dynamics should be expected in living tissues is unclear, because
cell divisions generate stress and remodeling events independently of local mechanical stability. Here, we address this question using a two-dimensional elastoplastic model in which
cell divisions are treated as active plastic events. We find that while
cell divisions fluidize the tissue below the passive yield stress, but preserve the marginal stability in the quasistatic limit. However, they also strongly suppress the system-spanning avalanches of
cell rearrangements, in constrast with the expected behavior in passive amorphous solids. Finally, we show that the avalanche supression originates from the energy balance in the system. Namely, the energy injected by
cell divisions allows for shear flow below the yield stress, but also provides a finite budget for rearrangements. These results suggest that proliferating tissues display the structural hallmarks of marginal amorphous solids while exhibiting much shorter-ranged correlations in dynamics, compared to passive amorphous solids.
Read the full abstract ▾
Materials Science
Competing crystallization pathways and cold crystallization kinetics in 10OS5 liquid crystal
Aleksandra Deptuch, Mirosława D. Ossowska-Chruściel, Janusz Chruściel et al. (+1 more)
The
liquid crystalline 4-pentylphenyl-4'-decyloxythiobenzoate is investigated in various temperature programs for determination of crystallization kinetics and glassforming properties. The Avrami model, Augis-Bennett method and isoconversional method are used. Cooling at the 25-30 K/min rate results in formation of the glass of the tilted smectic Y phase with the herring-bone order within layers. Slower cooling leads to the partial or total (2 K/min) crystallization of the metastable Cr2 phase, which during subsequent heating or annealing in a proper temperature transforms to another Cr1 phase. Heating from the vitrified smectic Y leads to cold crystallization of the pure Cr1 phase or the Cr1/Cr2 mix. Both Cr1 and Cr2 are conformationally disordered
crystal phases, which is indicated both by the melting
entropy values and the dielectric spectra. The results demonstrate that the energy released during cold crystallization can be tuned by thermal history, highlighting 10OS5 as a candidate for thermal energy storage applications.
Read the full abstract ▾
All authors Aleksandra Deptuch, Mirosława D. Ossowska-Chruściel, Janusz Chruściel, Ewa Juszyńska-Gałązka
Materials Science
Mechanical detection of sub-band mobilities of two-dimensional electron gas on reduced SrTiO$_3$(001) surface
Akash Gupta, Marcin Kisiel, Remy Pawlak et al. (+1 more)
The two-dimensional electron gas (2DEG) in reduced strontium titanate offers a versatile platform for
oxide electronics, yet its dissipation mechanisms under field driven charge fluctuations remain poorly understood. Here, we combine low-temperature atomic force microscopy with scanning tunnelling spectroscopy to probe the force and dissipation responses of a mechanical oscillator interacting with the STO 2DEG. The observation of Rydberg like image potential states by tunnelling experiments confirm the 2DEG formation, while dissipation spectroscopy reveals bias-dependent peaks linked to local electrostatic gating and charge redistribution within the 2DEG energy sub-bands. These features are quantitatively explained by variations in
quantum capacitance as carrier density is tuned by electric fields. Under
magnetic fields, dissipation peaks obey the Kohler's rule, allowing extraction of carrier mobilities in each sub-band. Our results establish a non-invasive AFM - based methodology for quantifying energy losses in
quantum oxides, providing new insights into charge dynamics relevant for spintronic applications.
Read the full abstract ▾
All authors Akash Gupta, Marcin Kisiel, Remy Pawlak, Ernst Meyer
Materials Science
Enhanced Impact Mitigation via 3D-Multilayered Material Architectures
Thomas Butruille, Joshua C. Crone and Carlos M. Portela
Materials designed by nature commonly exhibit functional grading and laminated structures, particularly when intended for enhanced impact protection. Synthetic materials have also found success in exploiting this concept with fully dense but spatially varying architectures, as is the case with advanced fiber-based composites. In the lightweight materials space, porous architected materials have shown benefits for extreme impact mitigation, proving to be advantageous in dissipating large amounts of energy per unit mass, but rarely harness the benefits of layering or functional grading in designs. Here, a design paradigm for lightweight multilayered materials towards high impact-mitigation efficacy is demonstrated, showing that the use of alternating monolithic and beam-based architectures leads to enhanced and predictable responses under extreme conditions. These layered, mass-equivalent `
heterostructures' with different ordering and proportions of octet and monolithic layers outperform single-architecture
lattices on a mass-normalized energy dissipation basis by >50% when subjected to supersonic microparticle impact. Through analysis that combines wave-propagation analysis, nonlinear finite element simulations, and post-impact crater reconstruction, layer-by-layer mechanical properties are mapped to crater formation and energy dissipation behaviors. This
heterostructure design framework offers a simple approach towards tuning failure and impact resistance of materials for protective applications from Whipple shields to sports equipment.
Read the full abstract ▾
Materials Science
Discovery of High-Voltage Magnesium-Ion Cathodes using Machine Learning and First-Principles Calculations
Jhon Rogelnor A. Florida and Edward Aris D. Fajardo
Developing high-performance cathode materials for magnesium-ion batteries (MIBs) remains challenging because Mg$^{2+}$ ions move slowly, and conventional materials exhibit low voltage outputs. In this study, machine learning and first-principles calculations were combined to investigate topological
quantum materials (TQMs) as a new class of cathode candidates. A modified
crystal graph convolutional neural network (mCGCNN) was used to screen 917 Mg-containing TQMs, identifying a small subset of materials with predicted voltages above 3 V and high volumetric capacities. Among these, Mg$_2$VO$_4$ and Mg$_6$MnO$_8$ were selected for detailed density functional theory (DFT) analysis. Formation energy and convex-hull calculations indicate that Mg$_x$VO$_4$ exhibits a fully stable magnesiation pathway, whereas Mg$_x$MnO$_8$ demonstrates minor metastability at intermediate compositions. The calculated voltage profiles yield average voltages of 3.66 V for Mg$_2$VO$_4$ and 4.06 V for Mg$_6$MnO$_8$, in good agreement with machine learning predictions. Electronic structure analysis, supported by Wannier interpolation, confirms that both materials are semiconducting, with valence bands dominated by O $2p$ states and conduction bands by transition-metal $d$ states, indicating a charge-transfer redox mechanism. Compared to conventional Mg cathodes, these TQMs exhibit higher voltages and competitive capacities, underscoring their potential for next-generation multivalent batteries. This study demonstrates that integrating machine learning with first-principles calculations offers an efficient approach for discovering and understanding novel cathode materials.
Read the full abstract ▾
Strongly Correlated Electrons
$H$-linear magnetoresistance in NbSe$_2$ due to impeded cyclotron motion
A. Kool, D. Pizzirani, P. Tinnemans et al. (+5 more)
Linear magnetoresistance (LMR) is a widespread phenomenon observed in a host of
quantum materials ranging from
semiconductor nanostructures to
quantum critical and strange metals. While multiple scenarios to explain LMR have been proposed, a complete understanding of the phenomenon remains elusive. Indeed, it is highly likely that the origin of LMR depends on the specific electronic state. Here, we report a study of the impact of disorder on the form of the magnetoresistance of the prototypical charge-density-wave (CDW) compound 2$H$-NbSe$_2$. The magnetoresistance is shown to exhibit strong qualitative and quantitative agreement with Boltzmann transport analysis incorporating impeded cyclotron motion (ICM). We identify the source of ICM in 2$H$-NbSe$_2$ as strong scattering sinks where the CDW order connects the high temperature
Fermi cylinders. Such unusual "hotspots" provide an explanation for the observed LMR as well as for the long-unexplained absence of
quantum oscillations inside the charge ordered state in 2$H$-NbSe$_2$. These findings provide strong evidence that ICM generates LMR in certain correlated metals.
Read the full abstract ▾
All authors A. Kool, D. Pizzirani, P. Tinnemans, S. Wiedmann, F. Flicker, J. van Wezel, N. E. Hussey, R. D. H. Hinlopen
Strongly Correlated Electrons
Magnetism and spin dynamics of Na$_5$Yb(MoO$_4$)$_4$: A weakly interacting rare-earth stretched diamond lattice
N. Rajeesh Kumar, J. Khatua, Changhyun Koo et al. (+8 more)
We report a comprehensive investigation of the structural and
magnetic properties of Na$_5$Yb(MoO$_4$)$_4$, a member of the stretched diamond
magnetic lattice family.
Neutron powder diffraction at 3.3~K confirms that the compound crystallizes in the tetragonal \textit{I4$_1$/a} space group, with a large interatomic separation of 6.33~Å between
magnetic Yb ions forming a three-dimensional stretched diamond framework.
Magnetic susceptibility and specific heat measurements reveal no evidence of long-range
magnetic order down to 60~mK. The low-temperature
magnetic behavior is governed by an effective $J_{\mathrm{eff}} = 1/2$ Kramers doublet ground state, well separated from excited
crystal-field levels, arising from the distorted dodecahedral oxygen coordination of Yb$^{3+}$. Density functional theory calculations within the DFT+$U$ framework indicate that exchange interactions between Yb ions are negligibly small, consistent with the long O–Mo–O super-superexchange pathways. The temperature dependence of the specific heat exhibits signatures of gapped
spin excitations, most likely originating from long-range dipolar correlations and further shaped by weak exchange interactions together with the strong single-ion anisotropy of the Yb moments.
Muon spin relaxation measurements reveal persistent low-energy
spin dynamics, indicating that dipolar correlations remain dynamic and are insufficient to stabilize static
magnetic order down to 50~mK. These results identify Na$_5$Yb(MoO$_4$)$_4$ as a rare example of a dipolar
quantum paramagnet in which single-ion physics and long-range dipolar interactions dominate, while exchange interactions are suppressed to the millikelvin energy scale.
Read the full abstract ▾
All authors N. Rajeesh Kumar, J. Khatua, Changhyun Koo, Izumi Umegaki, C. -E. Yin, C. -W. Wang, A. M. Strydom, H. -T. Jeng, Kwang-Yong Choi, R. Sankar, W. -T. Chen
Statistical Mechanics
Attractive statistical forces and Pauli crystal formation in trapped Fermi gases
Kawon Lee, Sangeun Oh, Young Woo Choi et al. (+1 more)
Exchange statistics endows identical particles with an effective "statistical potential", whose familiar exact form is two-body and purely repulsive for
fermions. Here we construct an exact collective many-body form: the thermodynamics of $N$ trapped ideal
fermions maps onto classical distinguishable particles governed by a single potential – exactly for harmonic confinement at all temperatures, and to leading semiclassical order for arbitrary potentials. The associated force separates canonically into pairwise contributions, which for $N\geq 3$ can turn attractive, governed by a simple
geometric criterion. Classical minimization reproduces observed few-body Pauli-
crystal symmetries and agrees with the $N=55$ ground-state probability maximum at sub-percent shell accuracy. Heating drives discrete structural transitions accompanied by a crossover of the strongest force from attractive to repulsive. Both the potential and its forces are directly computable from existing single-shot imaging data, turning
quantum exchange into measurable classical mechanics.
Read the full abstract ▾
All authors Kawon Lee, Sangeun Oh, Young Woo Choi, Jeong-Hyuck Park
Strongly Correlated Electrons
Emergent Vortex Ordering in a Multiflavor Pyrochlore-Lattice Compound GeCo$_2$O$_4$
Jiajun Mo, Otkur Omar, Shuangkui Guang et al. (+12 more)
Entangled
spin and orbital degrees of freedom provide a multiflavor route to novel
magnetic states inaccessible in conventional
spin systems. Here, we report the experimental identification of an emergent
vortex lattice in the multiflavor pyrochlore-
lattice compound GeCo$_2$O$_4$. By combining comprehensive
neutron scattering experiments with a regularized regression framework, we identify substantial Kitaev interactions among the nearest-neighboring Co$^{2+}$ pseudospins, which cooperate with
geometric frustration to stabilize the
vortex order. These results reveal an unexpected route to
vortex-
lattice order in a three-dimensional Kitaev-frustrated magnet and demonstrate a regularized protocol for
Hamiltonian determination in frustrated
quantum materials.
Read the full abstract ▾
All authors Jiajun Mo, Otkur Omar, Shuangkui Guang, Kazuki Iida, Kazuya Kamazawa, Fabio Orlandi, Wenyun Yang, Xiaobai Ma, Xiquan Zheng, Yingying Peng, Yuan Xiao, Shunhong Zhang, Oksana Zaharko, Xuefeng Sun, Shang Gao
Materials Science
Vacancy-Enhanced $N-N$ Bonding and Deep Level Complex Defect Formation in $\beta-Ga_2O_3$
Asiyeh Shokri, Yevgen Melikhov, Yevgen Syryanyy et al. (+2 more)
Nitrogen implantation can make $\beta-Ga_2O_3$ semi-insulating, but the atomic origin responsible for carrier trapping remains unresolved. Here, hybrid density functional theory is used to examine complexes derived from an interstitial-substitutional N pair, $N_{i9}-N_{OI}$, and effects of nearby O and Ga vacancies on $N-N$ bonding, stability, and electronic states. Within the configurations examined, N atoms favor co-localization. In selected Ga-vacancy-assisted complexes, the $N-N$ distance shortens to 1.09-1.19 $\mathring{\mathrm{A}}$ and exhibits electron localization consistent with substantial $N-N$ covalent character. Positive binding energies indicate favorable association relative to separated defects, although many of these complexes have high formation energies and are therefore more likely to be metastable products of implantation than abundant
equilibrium defects. Calculated N $K$-edge XANES spectra for two selected Ga-defect-assisted $N-N$ complexes reveal a pronounced sensitivity of the near-edge $\pi^*$ resonance to the local defect environment, providing an atomistic perspective on the experimentally observed
evolution toward molecular $N_{2}$ during annealing. Projected densities of states and
spin-density distributions show localized N-$2p$- and O-$2p$-derived states well inside the band gap. These vacancy-assisted N complexes therefore provide an atomistic mechanism for deep carrier trapping and current blocking rather than shallow acceptor doping in $\beta-Ga_2O_3$.
Read the full abstract ▾
All authors Asiyeh Shokri, Yevgen Melikhov, Yevgen Syryanyy, Maryna Chernyshova, Iraida N. Demchenko
Materials Science
Tailoring the material properties, nanostructure and grain alignment of Alnico magnets through micromagnetic simulations
Anda Elena Stanciu, Johann Fischbacher, Markus Gusenbauer et al. (+9 more)
Alnico magnets have gained renewed interest in the search for rare-earth free permanent magnets due to their high thermal stability and magnetisation. However, the limited coercivity of these shape-anisotropy-based
alloys constrains their performance. Starting from a reference Alnico sample, we realised a finite elements micromagnetic study of exchange-decoupled rods by varying their dimensions and interrod spacing across those observed experimentally. We computed the hysteresis properties by progressing from micromagnetic simulations of a small number of rods within the magnetostatic field of their neighbours to large systems treated statistically based on the distribution of orientations of the grains. We compared the coercivity of an isolated rod with that of the exchange-decoupled system to highlight the effect of magnetostatic interactions. We computed analytically the stray field acting on a single rod as a consequence of its surrounding rods in order to confirm the scaling of the coercivity with the packing fraction p. We explored how intrinsic material properties influence
magnetic behaviour by examining materials with different magnetocrystalline anisotropy constants and saturation polarisation values. Results from several hundred simulations were used to train a multi-layer perceptron regressor and predict the
magnetic properties as function of the dimensions of the rods, interrod spacing and orientation of the grains. With this approach, we highlight the underlying trends by which nanoscale structuring, intrinsic material properties and grain
alignment can be tailored to improve the
magnetic properties of Alnico
alloys.
Read the full abstract ▾
All authors Anda Elena Stanciu, Johann Fischbacher, Markus Gusenbauer, Alexander Kovacs, Harald Oezelt, Joachim Seland Graff, Patricia Carvalho, Anette Eleonora Gunnæs, Matej Zaplotnik, Espen Sagvolden, Spyros Diplas, Thomas Schrefl
Strongly Correlated Electrons
Staggered spin susceptibility at a two-dimensional antiferromagnetic quantum critical point
Y. Itoh
We report on the finite temperature staggered
spin susceptibility $\chi(Q)$ as a function of the mode-mode coupling constant $y_1$ in the self-consistent renormalization theory of two-dimensional
antiferromagnetic spin fluctuations with zero-point
quantum fluctuations just at the
quantum critical point ($y_0$ = 0). We find that the value $y_1$ = 0.1 is a criterion to classify the effect of the zero-point
spin fluctuations on the temperature dependence of $\chi(Q)$ into a Curie law for weak $y_1 < $ 0.1 and a Curie-Weiss type or a power law type for strong $y_1 > $ 0.1. The absence of a Curie-Weiss temperature can serve as an identifying criterion for QCP ($y_0$ = 0) in systems with weak mode-mode coupling ($y_1 <$ 0.1). Experimental application on the $y_1$ classification is shown to several itinerant layered
antiferromagnetic systems through an analysis of
nuclear spin-
lattice relaxation rates.
Read the full abstract ▾
Superconductivity
Nematicity in LaFeAsO single crystals studied by elastoresistance, high-resolution thermal expansion and shear-modulus measurements
X. C. Hong, S. Sauerland, L. Wang et al. (+10 more)
Nematicity in LaFeAsO single
crystals is studied by means of high-resolution thermal expansion, shear modulus, and elastoresistivity measurements. A softening of the shear modulus $C_{\rm 66}$ towards the structural phase transition at $T_{\rm S}$ is observed. In addition, a similar Curie-Weiss-like divergence of the nematic susceptibilities is found in the temperature dependence of both $\chi^{sh}$ and $\chi^{er}$, which are deduced from the shear modulus (sh) and the elastoresistivity (er) studies, respectively. These observations provide evidence for an electronic origin of nematicity in LaFeAsO. The characteristic energy of the coupling between the
lattice and the electronic degrees of freedom is deduced to $\sim$30~K. The comparison to corresponding measurements on BaFe$_2$As$_2$ single
crystals reveals a very similar temperature dependence of the shear modulus but yields contrasting results for $\chi^{er}$ : In BaFe$_2$As$_2$, $\chi^{er}$ diverges similarly as the uncoupled nematicity deduced from the shear modulus data as it is expected from the underlying Landau theory. In contrast, the Weiss temperatures of $\chi^{er}$ and $\chi^{sh}$ are significantly different in LaFeAsO. This difference is at odds with the commonly anticipated theories of resistivity anisotropy and electronic nematicity in iron pnictides.
Read the full abstract ▾
All authors X. C. Hong, S. Sauerland, L. Wang, F. Scaravaggi, A. U. B. Wolter, R. Kappenberger, S. Aswartham, S. Wurmehl, S. Sykora, F. Caglieris, B. Büchner, C. Hess, R. Klingeler
Mesoscale and Nanoscale Physics
Topological edge states of the hexagonal linear chain
M. Niţă
We study the eigenspectrum properties of a one-dimensional molecular chain composed of hexagonal unit
cells. The system features two alternating hopping parameters, resulting in a rich energy spectrum with both dispersive and flat bands. By analyzing the model under periodic and open boundary conditions, we identify two insulating phases separated by a gap-closing transition controlled by the ratio of hopping amplitudes. In the topological phase, realized when the hopping ratio falls below a critical value, edge states emerge that are exponentially localized at the boundaries of finite chains.
Read the full abstract ▾
Other Condensed Matter
Enhanced Photomultiplication Effect by Synergistic Integration of Hole-Blocking Layers and Trap Engineering in PM-OPDs
Awais Sarwar, Louis Conrad Winkler, Anncharlott Kusber et al. (+4 more)
Photomultiplication-type organic photodetectors (PM-OPDs) promise exceptional sensitivity for weak-light detection but typically suffer from a gain-bandwidth trade-off where high external
quantum efficiency (EQE) incurs large dark current and slow response times. Here, we demonstrate a fully
vacuum-deposited PM-OPD architecture that mitigates these limitations by integrating hole-blocking layers low-stoichiometry molecular trap engineering. We isolate discrete trapping sites that maximize positive space-charge accumulation by introducing m-MTDATA as a dedicated hole-trapping site at a low concentration (0.5 wt%) into a BDP-OMe:C60 bulk heterojunction. This engineered charge confinement triggers efficient field-assisted electron injection from the anode while remaining strictly below the threshold for localized percolation, effectively decoupling the photocurrent multiplication mechanism from trap-mediated dark current shunts. Consequently, the optimized device achieves a peak EQE exceeding 1100% at a reverse bias of -4 V. The optimized device exhibits a specific detectivity of 4x10^{12} Jones under -2 V reverse bias along with a cutoff frequency (f-3dB) of 22 kHz.
Read the full abstract ▾
All authors Awais Sarwar, Louis Conrad Winkler, Anncharlott Kusber, Fred Kretschmer, Karl Leo, Hans Kleemann, Johannes Benduhn
Quantum Gases
Universal Speed Limit in a Far-from-Equilibrium Bose Gas: Symmetry and Dynamical Decoherence
Jun-Cheng Liang and Bo Chen
Predicting universal transport coefficients in far-from-
equilibrium quantum systems remains a fundamental challenge. A paradigmatic example is the non-thermal fixed point (NTFP) of isolated Bose gases, where coherence spreads as $\ell^2(t) = C\hbar t/m$ with a universal constant $C$. While the scaling exponent $z=2$ is well established, the amplitude $C$ has remained elusive because the underlying particle cascade $n(k)\sim k^{-4}$ leads to a divergent kinetic energy, threatening the very existence of a constant speed limit. Here we resolve this paradox and present the first analytical, parameter-free prediction of a universal amplitude $C$. A deep interplay between
symmetry and dissipation is uncovered. The emergent weak U(1)
symmetry at the NTFP enforces a conserved total current, forcing the low-energy phase dynamics to obey a diffusive Langevin equation with noise entering as the divergence of a
stochastic current. This structure, combined with dynamical decoherence of high-momentum modes, yields a universal power-law momentum distribution $\tilde{f}(v)\sim(1+v^2)^{-3}$ (with $v=k\ell$) that naturally regularizes the ultraviolet divergence. From this, a parameter-free
geometric baseline $C=3$ is obtained, independent of microscopic details. The experimental value $C=3.4(3)$ [Martirosyan et al., Nature 647, 608 (2025)] is then shown to be quantitatively consistent with universal logarithmic corrections arising from a marginally irrelevant coupling at the fixed point. A new paradigm is thus established for predicting transport coefficients in strongly correlated non-
equilibrium systems:
symmetry constraints determine the low-energy effective theory, dynamical decoherence provides a natural ultraviolet completion, and scaling analysis delivers testable predictions moving beyond scaling exponents to quantitative amplitude prediction.
Read the full abstract ▾