Disordered Systems and Neural Networks
Learning About Learning: A Path from Spin Glasses to Artificial Intelligence
Denis D. Caprioti, Matheus Haas, Constantino F. Vasconcelos et al. (+1 more)
The Hopfield model, originally inspired by
spin glasses, occupies a central place at the intersection of statistical mechanics, neural networks, and artificial intelligence. Despite its conceptual simplicity and broad applicability, it is rarely integrated into the undergraduate physics curriculum. We present the Hopfield model as a pedagogically rich framework that naturally unifies core topics from the undergraduate physics curriculum and that provides a concise introduction based on concepts such as a model's energy function, dynamics, and pattern stability. We discuss practical aspects of its simulation and provide simulation codes. We also propose problems designed to mirror research practice, which can be included in undergraduate classes.
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All authors Denis D. Caprioti, Matheus Haas, Constantino F. Vasconcelos, Mauricio Girardi-Schappo
Soft Condensed Matter
Decoupling of single-particle and collective dynamics in arrested phase-separating glassy mixtures
Konstantin N. Moser, Christos N. Likos and Vittoria Sposini
We investigate the structure and dynamics of a hard colloid-
star polymer mixture in the range of its arrested phase separation, where an incipient demixing transition is interfering with a nearby vitrification line, focusing on the
protein limit (smaller hard component). Soft-hard mixtures present a rich dynamics, influenced by different parameters such as the concentration of the soft and hard components, the softness of the potential, and the size ratio between the two components. Using coarse-grained molecular dynamics simulations, we characterize the single-particle and collective dynamics of the hard colloidal tracers in the soft glassy
matrix. The hard tracers show diffusive behavior of the mean squared displacement accompanied by non-exponential relaxation of the intermediate scattering functions at intermediate length scales and non-Gaussian displacement distributions. Moreover, we show that the system exhibits arrested phase separation, leading to population splitting and decoupling between self- and collective dynamics of the hard colloids. Overall, we demonstrate that the interplay between arrested phase separation and glassiness leads to complex, multiscale phenomena that strongly influence the dynamics of the hard additives in the arrested
matrix formed by the soft colloids.
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Mesoscale and Nanoscale Physics
Observation of exceptional topology and nonlocal skin effect in Klein bottle electric circuits
Pengtao Lai, Xiangru Chen, Yugan Tang et al. (+7 more)
Symmetry and its representation play a crucial role in topological phases, including both Hermitian and non-Hermitian paradigms. In the presence of synthetic gauge field, spatial
symmetries should be projectively represented, which can modify the Brillouin
manifold. However, this is often overlooked in non-Hermitian systems. Here, we present that momentum-space non-symmorphic reflection
symmetry, a typical projective
symmetry, induce exceptional
topology and the nonlocal skin effect in a two-dimensional non-Hermitian electric
circuit. We observe the total topological charges 2, rather than 0, for all exceptional points in a Brillouin Klein bottle
manifold, and the phase transition when an exceptional point crosses the antiparallel boundary and flips its topological charge. We further observe a novel skin effect that the skin modes at one side are nonlocally connected to those on the opposite side separated by half of the reciprocal
lattice. Our results unveil the unique non-Hermitian phenomena enabled by the projective
symmetry, and open avenues for exploring the non-Hermitian
topology beyond Brillouin
torus manifold.
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All authors Pengtao Lai, Xiangru Chen, Yugan Tang, Yejian Hu, Zhenhang Pu, Hui Liu, Weiyin Deng, Hua Cheng, Zhengyou Liu, Shuqi Chen
Soft Condensed Matter
Aggregating swarms through morphology handling design contingencies: from the sweet spot to a rich expressivity
Jeremy Fersula, Nicolas Bredeche and Olivier Dauchot
Morphological computing, the use of the physical design of a
robot to ease the realization of a given task has been proven to be a relevant concept in the context of swarm robotics. Here we demonstrate both experimentally and numerically, that the success of such a strategy may heavily rely on the type of policy adopted by the
robots, as well as on the details of the physical design. To do so, we consider a swarm of
robots, composed of Kilobots embedded in an exoskeleton, the design of which controls the propensity of the
robots to align or anti-align with the direction of the external force they experience. We find experimentally that the contrast that was observed between the two morphologies in the success rate of a simple phototactic task, where the
robots were programmed to stop when entering a light region, becomes dramatic, if the
robots are not allowed to stop, and can only slow down. Building on a faithful physical model of the self-aligning dynamics of the
robots, we perform numerical simulations and demonstrate on one hand that a precise tuning of the self-aligning strength around a sweet spot is required to achieve an efficient phototactic behavior, on the other hand that exploring a range of self-
alignment strength allows for a rich expressivity of collective behaviors.
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Strongly Correlated Electrons
Machine learning nonequilibrium phase transitions in charge-density wave insulators
Yunhao Fan, Sheng Zhang and Gia-Wei Chern
Nonequilibrium electronic forces play a central role in voltage-driven phase transitions but are notoriously expensive to evaluate in dynamical simulations. Here we develop a machine learning framework for adiabatic
lattice dynamics coupled to nonequilibrium electrons, and demonstrate it for a gating induced
insulator to metal transition out of a charge density wave state in the Holstein model. Although exact electronic forces can be obtained from nonequilibrium Green's function (NEGF) calculations, their high computational cost renders long time dynamical simulations prohibitively expensive. By exploiting the locality of the electronic response, we train a neural network to directly predict instantaneous local electronic forces from the
lattice configuration, thereby bypassing repeated NEGF calculations during time
evolution. When combined with Brownian dynamics, the resulting machine learning force field quantitatively reproduces domain wall motion and nonequilibrium phase transition dynamics obtained from full NEGF simulations, while achieving orders of magnitude gains in computational efficiency. Our results establish direct force learning as an efficient and accurate approach for simulating nonequilibrium
lattice dynamics in driven
quantum materials.
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Materials Science
Anisotropic anomalous Hall effect in distorted kagome GdTi3Bi4
Avdhesh K. Sharma, Bo Tai, Subhajit Roychowdhury et al. (+5 more)
Topological kagome magnets offer a rich landscape for exploring the intricate interplay of
quantum interactions among geometry,
topology,
spin, and correlation. GdTi3Bi4 crystallizes in layered Ti based kagome nets intertwined with zigzag Gd chains along the a axis and orders antiferromagnetically below 15 K. Here, we present the temperature and field dependent electrical transport of GdTi3Bi4 in different directions. The material exhibits anomalous
Hall conductivity (AHC) of 410 S cm-1 at 2 K for B parallel c and it is completely absent for B parallel a, despite the similar magnetization observed in both orientations. This behavior is quite contradictory, as anomalous
Hall effect (AHE) typically scales with the magnetization. Through first principles calculations, it is demonstrated that in the presence of time reversal
symmetry broken by the Gd 4f sublattice and
spin orbit coupling, the magnetization direction controls the orbital mixing in the Ti t2g bands, relocating Berry
curvature hot spots and producing the observed orientation selective AHC. The results establish GdTi3Bi4 as platform for investigating new avenues of AHE, such as directional AHE, and thus shed new light on the intricate coupling between
magnetic and electronic structures, paving the way for exploring novel
quantum phenomena.
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All authors Avdhesh K. Sharma, Bo Tai, Subhajit Roychowdhury, Premakumar Yanda, Ulrich Burkhardt, Xiaolong Feng, Claudia Felser, Chandra Shekhar
Quantum Gases
Excitation spectrum of a bright solitary wave in a Bose-Einstein condensate and its connection with the Higgs and the Goldstone modes
G. M. Kavoulakis
We consider the problem of Bose-Einstein condensed atoms, which are confined in a (quasi) one-dimensional toroidal potential. We focus on the case of an effective attractive interaction between the atoms. The formation of a localized blob (i.e., a “bright" solitary wave) for sufficiently strong interactions provides an example of spontaneous
symmetry breaking. We evaluate analytically and numerically the excitation spectrum for both cases of a homogeneous and of a localized density distribution. We identify in the excitation spectrum the emergence of the analogous to the Goldstone and the
Higgs modes, evaluating various relevant observables, gaining insight into these two fundamental modes of excitation.
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Strongly Correlated Electrons
Magnons in multiorbital Hubbard models, from Lieb to kagome
Teng-Fei Ying, Hugo U. R. Strand, Benjamin T. Zhou et al. (+1 more)
We investigate the
magnetic orders and excitations in a half-filled Hubbard model that continuously interpolates between the Lieb and kagome
lattices. Using self-consistent Hartree-Fock approximation combined with the Bethe-Salpeter equation in the random phase approximation, we map the $U-t'$ phase diagram of the Lieb-kagome
lattices and compute real-frequency transverse
spin susceptibilities, i.e., the
magnon spectra. Dynamical mean-field theory and exact diagonalization are used as complementary checks of static
magnetic phases. In particular, besides gapless Goldstone
magnons, the
symmetry-broken ferrimagnetic and
antiferromagnetic phases also exhibit gapped
Higgs magnon bands, which originate from amplitude fluctuations in the order parameter characterizing spontaneous
symmetry breaking.
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All authors Teng-Fei Ying, Hugo U. R. Strand, Benjamin T. Zhou, Erik G. C. P. van Loon
Materials Science
PEG- and PVP-assisted wet-chemical synthesis of ZnS nanocrystals via hydrothermal and co-precipitation methods for route-dependent structural and bandgap tuning
Rao Uzair Ahmad, Nasir Javed and Falak Sher
Zinc sulphide (ZnS) is a non-toxic, wide-bandgap II-VI
semiconductor with well-established optoelectronic properties. This work presents a systematic, concentration-dependent comparison of PEG and PVP across two scalable aqueous routes, linking ligand chemistry to crystallite size and bandgap shifts. ZnS
quantum dots (QDs) were synthesized using
polymer-assisted wet-chemical methods, hydrothermal processing and room-temperature co-precipitation. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were used as capping
agents to examine their influence on particle growth, dispersion, and optical behaviour. Room-temperature co-precipitation produced QDs with crystallite sizes as small as 2.03 nm, whereas hydrothermal synthesis at elevated temperature yielded larger crystallites exceeding 6 nm. X-ray diffraction confirmed cubic zinc-blende ZnS in all samples, with peak broadening and small
lattice-parameter variations consistent with nanoscale dimensions. UV-visible absorption spectra showed systematic shifts of the absorption edge, with optical bandgap values ranging from 3.60 to 3.80 eV, consistent with size-dependent
quantum confinement.
Fourier-transform infrared spectroscopy and dynamic light scattering verified effective
polymer capping and particle size distribution, with PVP providing stronger growth suppression and improved dispersion compared to PEG. Overall, the results highlight how synthesis route and
polymer-nanocrystal interactions govern the structural and optical properties of ZnS QDs. The demonstrated bandgap tuning and improved dispersion with PVP are relevant for UV optoelectronic coatings and QD-based layers used in photodetectors and LED interfaces.
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Materials Science · Cross-listed from physics.optics
Exciton coherence propagation measured with non-local four-wave mixing micro-spectroscopy
Mateusz Raczyński, Amadeusz Dydniański, Karolina Ewa Połczyńska et al. (+8 more)
Coherence transfer is a multi-disciplinary topic of interest, including chemistry, biology and physics. In
quantum technologies, achieving non-local coherent coupling between solid-state
qubits is of the utmost importance. Here, we demonstrate that
excitons - i.e. electron-hole pairs bound by the Coulomb force within a
quantum well - can act as a medium for mesoscopic optical coherence transfer in
semiconductors. To this end, we use a femtosecond
laser pulse to resonantly generate
excitons within the light cone. These
excitons can then either recombine radiatively or scatter out of the light cone, gaining an in-plane momentum in the process. In samples without disorder, such as the CdTe
quantum wells used here, the resulting fast
excitons can diffuse over mesoscopic distances before recombining radiatively. Using coherent nonlinear micro-spectroscopy, we carry out
exciton time-of-flight measurements. Specifically, we monitor the spatio-temporal propagation of launched
exciton wave packets, selectively observing their coherence or density on a scale of up to 10$\,\mu$m. Our proof-of-principle experiment demonstrates that free
excitons inherit a phase modulation from the optical pulsed excitation and can generate coherent links within excitonic
circuits, offerring a higher level of miniaturisation and compactness than photonic or polaritonic architectures.
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All authors Mateusz Raczyński, Amadeusz Dydniański, Karolina Ewa Połczyńska, Gabriela Szwed, Adam Szczerba, Jin-Woo Jung, Gilles Nogues, Wolfgang Langbein, Piotr Kossacki, Wojciech Pacuski, Jacek Kasprzak
Soft Condensed Matter
Modulators Selectively Reshape alpha-Synuclein Phase Transitions
Holly Masson, Massimiliano Paesani and Ioana M. Ilie
Protein phase transitions govern numerous diseases, including neurodegenerative disorders such as Parkinson's and Alzheimer's. In Parkinson's disease, distinct species of the
protein alpha-synuclein undergo phase transitions from highly disordered to ordered beta-rich states. The emerging species and transitions between them can be reshaped by chaperones, small molecules, peptides or antibodies. Here, we use coarse-grained simulations to understand the effect of modulators on the thermodynamics and kinetics of alpha-synuclein transformations and phase transitions. Each
protein is represented as a single morphing particle that transforms from a soft sphere (disordered state) to a hard spherocylinder (beta-rich state), while modulators are modeled as soft isotropic particles mimicking small peptides. The results show that purely repulsive modulators do not alter the final outcome, i.e. fibrils form following the same mechanisms independently of the modulator concentration. Attractive interactions towards the disordered
protein slow down fibril formation in a dose-dependent manner by stabilizing intermediate species, and strong attraction yields persistent disordered heteroclusters. In contrast, specific attraction to the beta-rich state results in shorter fibrils through direct modulator surface "capping" that introduce kinetic barriers to monomer templating at the fibril ends and inhibit lateral attachment. Together, these results link modulator properties and environmental conditions to the effects on nucleation, fibril elongation and off-pathway trapping, providing a quantitative roadmap for selecting modulator properties and strategies that redirect phase transitions toward desirable endpoints. Additionally, they provide guiding principles for the development of intervention strategies and the engineering of novel materials with tunable and responsive properties.
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Materials Science · Cross-listed from math.FA
Phase-field approximation of sharp-interface energies accounting for lattice symmetry
Sergio Conti, Vito Crismale, Adriana Garroni et al. (+1 more)
We present a phase-field approximation of sharp-interface energies defined on partitions, designed for modeling grain boundaries in polycrystals. The independent variable takes values in the orthogonal group $\mathrm{O}(d)$ modulo a
lattice point group $\mathcal{G}$, reflecting the crystallographic
symmetries of the underlying
lattice. In the sharp-interface limit, the surface energy exhibits a Read-Shockley-type behavior for small misorientation angles, scaling as $\theta|\log\theta|$. The regularized functionals are applicable to grain growth simulation and the reconstruction of grain boundaries from imaging data.
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All authors Sergio Conti, Vito Crismale, Adriana Garroni, Annalisa Malusa
Mesoscale and Nanoscale Physics
Reconfigurable Oxide Nanoelectronics by Tip-induced Electron Delocalization
Chengyuan Huang, Changjian Ma, Mengke Ha et al. (+15 more)
Reconfigurable
oxide nanoelectronics, enabled by conductive atomic force microscope (cAFM) lithography, have established complex
oxide interfaces as a promising platform for
quantum engineering that harnesses emergent phenomena for advanced functionalities. However, this cAFM nanofabrication process can only occur in the air, with simultaneous device decay described under the "water-cycle" writing mechanism. These restrictions pose ongoing challenges for device optimization in the
quantum regime at mK temperatures. Here, we demonstrate a "waterless" cAFM lithography approach that is compatible with
vacuum and cryogenic environments. Through oxygen vacancy engineering at the LaAlO$_3$/SrTiO$_3$ interface, we have achieved nonvolatile and reconfigurable cAFM control of nanoscale interfacial polaron-electron
liquid transition at mK temperatures with an ultrafine line resolution of 0.85 nm. Supported by first-principles calculations and drift-
diffusion modeling, we show that tip-controlled oxygen vacancy electromigration plays a key role. This advancement bridges reconfigurable device fabrication and concurrent characterization in situ at mK temperatures, and establishes a versatile Hubbard toolbox for engineering programmable
quantum phases in correlated
oxides.
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All authors Chengyuan Huang, Changjian Ma, Mengke Ha, Longbing Shang, Zhenlan Chen, Qing Xiao, Zhiyuan Qin, Danqing Liu, Haoyuan Wang, Dawei Qiu, Qianyi Zhao, Ziliang Guo, Yanling Liu, Dingbang Chen, Chengxuan Ye, Zhenhao Li, Chang-Kui Duan, Guanglei Cheng
Superconductivity
Magnetic field decouples nodeless surface and nodal bulk orders in PdTe
Atanu Mishra, Ghulam Mohmad, Kiran Bansal et al. (+4 more)
Selective spectroscopic disentanglement of surface and bulk
quantum orders remains an outstanding challenge in condensed matter physics. The candidate topological
superconductor PdTe has recently been proposed to host a nodeless surface gap on top of a nodal bulk state, but their direct identification and mutual coupling remained experimentally elusive. Here, we employ
magnetic-field-dependent Andreev reflection spectroscopy to spectroscopically disentangle these components. At zero
magnetic field, the spectra exhibit a BCS-like gap structure, consistent with dominant transport through a fully gapped surface superconducting state. Strikingly, even a weak
magnetic field leads to an abrupt suppression of the Andreev-enhanced conductance (AEC), while a residual AEC, attributable to the nodal bulk state, persists to much higher
magnetic fields. The transition is accompanied by pronounced
magnetic hysteresis pointing to the existence of
vortex dynamics at low fields. Our findings suggest that the nodal bulk gap facilitates early
vortex entry, which in turn disrupts the fragile surface superconductivity. These results establish a field-tunable decoupling of surface and bulk superconductivity and illustrate how distinct gap
topologies can shape the global superconducting order in multichannel systems.
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All authors Atanu Mishra, Ghulam Mohmad, Kiran Bansal, Mohd Monish, Pankaj Kumar, Chandrasekhar Yadav, Goutam Sheet
Materials Science
High isothermal magnetocaloric effect in La(Fe,Si)13 based alloys
A.P. Kamantsev, Yu.S. Koshkid`ko, O.E. Kovalev et al. (+4 more)
This work investigates the magnetocaloric effect (MCE) in LaFe_{11.6}Si_{1.4} and LaFe_{11.78}Mn_{0.41}Si_{1.32}H_{1.6}
alloys under adiabatic {\Delta}T and isothermal {\Delta}Q conditions in a
magnetic field of {\mu}_{0}H = 1.8 T. The studied samples exhibited high reproducibility of the {\Delta}Q-effect upon cyclic
magnetic field application, which is of critical importance for
magnetic cooling systems.The LaFe_{11.78}Mn_{0.41}Si_{1.32}H_{1.6}
alloy demonstrate high values of the isothermal MCE, with a maximum {\Delta}Q = 3400 J/kg in a
magnetic field of {\mu}0H = 1.8 T near the Curie temperature (TC) of 275 K. This value is 2.5 times higher than the well-known corresponding values for pure Gd at room temperature. Furthermore, the structural and
magnetic properties of LaFe13-xSix-based
alloys with Cr and Co additions were investigated using density functional theory calcula-tions. It was shown that the addition of Cr leads to a decrease in the
equilibrium volume, i.e., to a com-pression of the
crystal lattice, whereas Co addition causes its expansion. These changes are expected to increase or decrease the T_{C}, respectively.
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All authors A.P. Kamantsev, Yu.S. Koshkid`ko, O.E. Kovalev, N.Yu. Nyrkov, A.V. Golovchan, A.A. Amirov, A.M. Aliev
Soft Condensed Matter
Rheofluidics: frequency-dependent rheology of single drops
Matteo Milani, Wenyun Wang, Lorenzo Russotto et al. (+4 more)
We present Rheofluidics, a microfluidic technique that measures the frequency-dependent rheology of individual micron-scale objects. We apply oscillatory hydrodynamic stresses by flowing them through channels with modulated constrictions, and measure their deformation. Unlike bulk rheology, which measures collective properties, Rheofluidics provides heretofore unattainable measurements of individual particles. We apply Rheofluidics to discover frequency-dependent surface tension of surfactants, very high-frequency viscoelasticity of microgels and unexpected frequency-dependent bending modulus of vesicles.
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All authors Matteo Milani, Wenyun Wang, Lorenzo Russotto, Weiyu Zong, Kevin Jahnke, David A. Weitz, Stefano Aime
Superconductivity
Observation of Time-Reversal Symmetry Breaking in the Type-I Superconductor YbSb$_2$
Anshu Kataria, Shashank Srivastava, Dibyendu Samanta et al. (+9 more)
The spontaneous breaking of time-reversal
symmetry is a hallmark of unconventional superconductivity, typically observed in type-II
superconductors. Here, we report evidence of time-reversal
symmetry breaking in the type-I
superconductor YbSb$_2$. Zero-field $\mu$SR measurements reveal spontaneous internal
magnetic fields emerging just below the superconducting transition, while transverse-field $\mu$SR confirms a fully gapped type-I superconducting state. Our first-principles calculations identify YbSb$_2$ as a ${\mathbb Z}_2$ topological metal hosting a Dirac nodal line near the
Fermi level.
Symmetry analysis within the Ginzburg Landau framework indicates an internally antisymmetric nonunitary triplet (INT) state as the most probable superconducting ground state. Calculations based on an effective low-energy model further demonstrate that this INT state hosts gapless Majorana surface modes, establishing YbSb$_2$ as a topological
superconductor. Our results highlight YbSb$_2$ as a unique material platform where type-I superconductivity coexists with triplet-pairing and nontrivial
topology.
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All authors Anshu Kataria, Shashank Srivastava, Dibyendu Samanta, Pushpendra Yadav, Poulami Manna, Suhani Sharma, Priya Mishra, Joel Barker, Adrian D. Hillier, Amit Agarwal, Sudeep Kumar Ghosh, Ravi Prakash Singh
Statistical Mechanics · Cross-listed from physics.bio-ph
Noise enhances odor source localization
Francesco Marcolli, Martin James and Agnese Seminara
We address the problem of inferring the location of a target that releases odor in the presence of
turbulence. Input for the inference is provided by many sensors scattered within the odor plume. Drawing inspiration from distributed chemosensation in biology, we ask whether the accuracy of the inference is affected by proprioceptive noise, i.e., noise on the perceived location of the sensors. Surprisingly, in the presence of a net fluid flow, proprioceptive noise improves
Bayesian inference, rather than degrading it. An optimal noise exists that efficiently leverages additional information hidden within the geometry of the odor plume. Empirical tuning of noise functions well across a range of distances and may be implemented in practice. Other sources of noise also improve accuracy, owing to their ability to break the spatiotemporal correlations of the turbulent plume. These counterintuitive benefits of noise may be leveraged to improve sensory processing in biology and robotics.
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Mesoscale and Nanoscale Physics
Hexagonal Warping Control of Exceptional Points in Topological Insulator–Ferromagnetic Heterojunctions
Md Afsar Reja and Awadhesh Narayan
Exceptional points (EPs) are non-Hermitian degeneracies, where both
eigenvalues and eigenvectors coalesce, which are fundamentally distinct from their Hermitian counterparts. In this study, we investigate the influence of hexagonal warping on EPs emerging at the interfaces between topological
insulators and ferromagnets. We demonstrate that the presence of the warping term plays a crucial role in determining the locations of the EPs. Furthermore, we show that the number as well as the positions of EPs emerging at such junctions can be tuned by an applied
magnetic field. Our results, in line with previous studies on topological
insulator-ferromagnet junctions, suggest them as a promising platform for realizing non-Hermitian physics.
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Soft Condensed Matter
Tuning cholesteric cellulose nanocrystal self-assembly in spherical confinement via salt and sonication
Diogo Vieira Saraiva, Anne Meike Hogeweg and Lisa Tran
Cellulose nanocrystals (CNCs) self-assemble into cholesteric
liquid crystals that produce structural color upon solvent removal. Although most studies examine this process in planar films, confinement within micron-sized water-in-oil droplets provides a powerful platform for resolving self-assembly dynamics in real time. Here, we investigate how two common pitch-tuning strategies, sodium chloride addition and tip sonication, govern the kinetics and structure of CNC self-assembly under spherical confinement. Polarized optical microscopy timelapses capture the
evolution from isotropic suspension through tactoid nucleation and annealing to kinetic arrest and final buckling. Consistent with prior work, pitch-concentration analysis reveals a universal post-arrest regime governed by droplet shrinkage. Beyond this established behavior, we identify a pre-arrest regime in which pitch decreases rapidly and whose kinetics accelerate with increasing salt concentration and sonication dose. These parameters shift the onset of cholesteric order and gelation, thereby tuning the concentration window for tactoid coalescence. Together, these results establish droplet confinement as a quantitative platform for probing out-of-
equilibrium CNC self-assembly and for kinetically programming structurally colored soft materials.
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Strongly Correlated Electrons
Collinear $p$-wave magnetism and hidden orbital ferrimagnetism
Valentin Leeb and Johannes Knolle
In the absence of
spin-orbit coupling, collinear magnets are classified as even-wave magnets, i.e., either ferro-, antiferro-, or altermagnets. It is based on the belief that collinear magnets always feature an inversion-symmetric band structure, which forbids odd-wave magnetism. Here, we show that collinear magnets, which break time reversal
symmetry in the non-
magnetic sector, can have an inversion
symmetry broken band structure and lead to unconventional types of collinear magnets. Hence, collinear odd-wave magnets do exist, and we explain that a
magnetic field-induced Edelstein effect is their unique signature. We propose minimal models based on the coexistence of AFM order with compensated loop current orders for all types of collinear magnets. Our work provides a new perspective on collinear magnets and the
spin-space group classification.
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Strongly Correlated Electrons
Sliding Charge Density Wave observed through Band Structure
S. Mandal, D. Ghoneim, A.A. Sinchenko et al. (+7 more)
An incommensurate CDW may have the ability to slide, i.e., to generate an excess of current when the system is submitted to an external field. Sliding phenomenon is closely related to deformation of the periodic
lattice distortion associated to the CDW. In principle, however, the sliding state can also be observed through the band structure. Here we show that broken
symmetry in k-space is observed by Angle-Resolved Photoemission Spectroscopy (ARPES) in the sliding regime of TbTe$_3$, which could be consistent with theoretical predictions.
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All authors S. Mandal, D. Ghoneim, A.A. Sinchenko, V.L.R. Jacques, K. Wang, L. Ortega, J. Avila, P. Dudin, A. Tejeda, D. Le Bolloch
Soft Condensed Matter
Janus Polymeric Giant Vesicles on Demand: A Predictive Phase Separation Approach for Efficient Formation
Eloise Equy, Emmanuel Ibarboure, Eric Grelet et al. (+1 more)
Janus particles, with their intrinsic asymmetry, are attracting major interest in various applications, including emulsion stabilization, micro/nanomotors, imaging, and drug delivery. In this context, Janus polymersomes are particularly attractive for synthetic
cell development and drug delivery systems. While they can be achieved by inducing a phase separation within their membrane, their fabrication method remains largely empirical. Here, we propose a rational approach, using Flory-Huggins theory, to predict the self-assembly of amphiphilic block copolymers into asymmetric Janus polymersomes. Our predictions are experimentally validated by forming highly stable Janus
giant unilamellar vesicles (JGUVs) with a remarkable yield exceeding 90% obtained from electroformation of various biocompatible block copolymers. We also present a general phase diagram correlating mixing energy with polymersome morphology, offering a valuable tool for JGUV design. These polymersomes can be extruded to achieve quasi-monodisperse vesicles while maintaining their Janus-like morphology, paving the way for their asymmetric functionalization and use as active carriers.
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All authors Eloise Equy, Emmanuel Ibarboure, Eric Grelet, Sebastien Lecommandoux
Superconductivity
Decoupled interband pairing in a bilayer iron-based superconductor evidenced by ultrahigh-resolution ARPES
Shichong Wang, Yuanyuan Yang, Yang Li et al. (+11 more)
We present direct experimental evidence of a weakly coupled multiband superconducting state in the
bilayer iron-based
superconductor ACa$_2$Fe$_4$As$_4$F$_2$ (A = K, Cs) via ultrahigh-resolution angle-resolved photoemission spectroscopy (ARPES). Remarkably, the K-containing compound exhibits two distinct transition temperatures, corresponding to two separate sets of
bilayer-split bands, as evidenced by temperature-dependent superconducting gap and spectral weight near the
Fermi energy, while its Cs counterpart displays conventional single transition behavior. These experimental observations are well described by the weakly coupled two-band model of Eilenberger theory, which identifies suppressed interband pairing interactions between the
bilayer-split bands as the key mechanism. By exploring
quantum phenomena in the weak-coupling limit within a multiband system, our findings pave the way for engineering exotic superconductivity via band-selective pairing control.
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All authors Shichong Wang, Yuanyuan Yang, Yang Li, Wenshan Hong, Huaxun Li, Shaofeng Duan, Lingxiao Gu, Haoran Liu, Jiongyu Huang, Jianzhe Liu, Dong Qian, Guanghan Cao, Huiqian Luo, Wentao Zhang
Strongly Correlated Electrons
Role of Disorder in Governing the Magnetic Properties of Cu2IrO3
Priyanka Yadav, Sumit Sarkar, Vishal Kumar et al. (+6 more)
Cu$_2$IrO$_3$ is a honeycomb iridate which has been studied recently as a candidate Kitaev
quantum spin liquid. Its
magnetic ground state however, has been reported to be
quantum disordered,
spin glassy, or magnetically ordered depending on synthesis details. We have prepared a Cu$_2$IrO$_3$ sample with large antisite disorder and studied in detail its structure (global and local), charge states, and thermodynamic properties to try to quantify and characterize the disorder and its connection to the
magnetic ground state. X-ray diffraction, Extended x-ray absorption fine structure(EXAFS) and X-ray pair distribution function analysis revealed a large site disorder ($\sim$25%), while XPS and XANES reveal mixed valence of Cu and Ir following Cu$^{1+}$ + Ir$^{4+}$ $\rightarrow$ Cu$^{2+}$ + Ir$^{3+}$. This combination of site disorder and charge redistribution generates competing
antiferromagnetic interactions and
magnetic frustration, resulting in dynamically fluctuating AFM clusters near 80K that freeze below 29K. These results demonstrate the crucial role of synthesis dependent disorder in determining the
magnetic ground state of Cu$_2$IrO$_3$.
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All authors Priyanka Yadav, Sumit Sarkar, Vishal Kumar, Sanjay Singh, Martin A Karlsen, Martin Etter, Sourav Chowdhury, Subhajit Nandy, Yogesh Singh
Soft Condensed Matter
Magnetically Driven Elastic Microswimmers: Exploiting Hysteretic Collapse for Autonomous Propulsion and Independent Control
Theo Lequy and Andreas M. Menzel
When swimming at low Reynolds numbers, inertial effects are negligible and reciprocal movements cannot induce net motion. Instead,
symmetry breaking is necessary to achieve net propulsion. Directed swimming can be supported by
magnetic fields, which simultaneously provide a versatile means of remote actuation. Thus, we analyze the motion of a straight microswimmer composed of three magnetizable beads connected by two elastic links. The swimming mechanism is based on oriented external
magnetic fields that oscillate in magnitude. Through induced reversible hysteretic collapse of the two segments of the swimmer, the two pairs of beads jump into contact and separate nonreciprocally. Due to higher-order hydrodynamic interactions, net displacement results after each cycle. Different microswimmers can be tuned to different driving amplitudes and frequencies, allowing for simultaneous independent control by just one external
magnetic field. The swimmer geometry and
magnetic field shape are optimized for maximum swimming speed using an evolutionary optimization strategy. Thanks to the simple working principle, an experimental realization of such a microrobot seems feasible and may open new approaches for microinvasive medical interventions such as targeted drug delivery.
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Statistical Mechanics
Curvature-driven shifts of the Potts transition on spherical Fibonacci graphs: a graph-convolutional transfer-learning study
Zheng Zhou, Xu-Yang Hou and Hao Guo
We investigate the
ferromagnetic $q$-state Potts model on spherical Fibonacci graphs. These graphs are constructed by
embedding quasi-uniform sites on a sphere and defining interactions via a chord-distance cutoff chosen to yield a network approximating four-neighbor connectivity. By combining Swendsen-Wang cluster Monte Carlo simulations with graph convolutional networks (GCNs), which operate directly on the adjacency structure and node
spins, we develop a unified phase-classification framework applicable to both regular planar
lattices and curved, irregular spherical graphs.
Benchmarks on planar
lattices demonstrate an efficient transfer strategy: after a fixed binarization of Potts
spins into an effective Ising variable, a single GCN pretrained on the Ising model can localize the transition region for different $q$ values without retraining. Applying this strategy to spherical graphs, we find that
curvature- and defect-induced connectivity irregularities produce only modest shifts in the inferred transition temperatures relative to planar baselines. Further analysis shows that the
curvature-induced shift of the critical temperature is most pronounced at small $q$ and diminishes rapidly as $q$ increases; this trend is consistent with the physical picture that, in two dimensions, the Potts model undergoes a transition from a continuous phase transition to a weakly first-order one for $q>4$, accompanied by a pronounced reduction of the correlation length.
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Quantum Gases · Cross-listed from quant-ph
Impact of Boundary Conditions on the Double-Kicked Quantum Rotor
Victoria Motsch, Nikolai Bolik and Sandro Wimberger
We study the on-resonance
Spin-1/2 Double Kicked Rotor, a periodically driven
quantum system that hosts topological phases. Motivated by experimental constraints, we analyze the effects of open and periodic boundary conditions in contrast to the idealized case of infinite momentum space. As a bulk probe for topological invariants, we focus on the Mean
Chiral Displacement (MCD) and show that it exhibits a pronounced sensitivity to boundary conditions, which can be traced to the dynamics in momentum space. Under open boundaries, states that would otherwise extend freely become localized at the edges of the finite momentum space, forming quasienergy edge states. While the bulk response measured by the MCD is strongly affected once the evolving wave packet reaches the boundaries, the persistence of these edge states still reflects the bulk-edge correspondence and provides reliable signatures of topological transitions.
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Mesoscale and Nanoscale Physics
Self-oscillations induced by self-induced torque in magnetic double tunnel junction
R. Arun, R. Gopal, V. K. Chandrasekar et al. (+1 more)
Self-oscillations of the magnetization due to self-induced torque (SIT) in a
magnetic double tunnel junction that consists of perpendicularly polarized, pinned and free layers is investigated along with the field-like torque (FLT). The associated Landau-Lifshitz-Gilbert-Slonczewski equation is numerically analysed to exhibit the oscillations of magnetization driven by the current. From the numerical analysis, we show that the SIT is essential to generate oscillations in the order of GHz and without it the magnetization reaches steady state after exhibiting switching. Without FLT, the frequency of the oscillations decreases with the current while the power of oscillations increases. In the presence of the negative strength of the FLT the power spectral density confirms that the frequency, power and the Q-factor increase with the current. Also the tunability range and the rate at which the frequency enhances increase with the magnitude of the FLT.
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All authors R. Arun, R. Gopal, V. K. Chandrasekar, M. Lakshmanan
Strongly Correlated Electrons
Field-induced magnetic phase transitions and transport anomalies in GdAlSi
Zheng Li, Sheng Xu, Yi-Yan Wang et al. (+6 more)
Magnetic topological materials hosting non-zero Berry
curvature have emerged as a focus of intensive research due to their exceptional magnetoelectric coupling phenomena and potential applications in next-generation spintronic devices. In this work, we successfully synthesized high-quality GdAlSi single
crystals, a prototypical member of RAlX (R = rare earth elements; X = Si/Ge) family that has been theoretically predicted to sustain a non-trivial Weyl semimetal state. Through systematic investigations of
magnetic and transport properties, we identified two successive
antiferromagnetic transitions at critical temperatures TN1 31.9 K and TN2 31.1 K, as evidenced by temperature-dependent resistivity,
magnetic susceptibility, and specific heat measurements. Notably, applied
magnetic fields exceeding 8 T induce a third
magnetic transition (TN3), generating a cascade of metamagnetic transitions that collectively form a dendritic phase diagram. This complex
magnetic behavior is attributed to the interplay between localized Gd-4f moments and itinerant conduction electrons, possibly mediated by Dzyaloshinskii-Moriya interactions. Transport measurements revealed striking stepwise anomalies in magnetoresistance when crossing phase boundaries, accompanied by pronounced hysteresis loops arising from
magnetic moment flopping processes. Our results not only establish GdAlSi as a rich platform for investigating correlated topological states, but also demonstrate its potential for engineering topological phase transitions through
magnetic symmetry manipulation in Weyl semimetals.
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All authors Zheng Li, Sheng Xu, Yi-Yan Wang, Tian-Hao Li, Shu-Xiang Li, Jin-Jin Wang, Jun-Jian Mi, Qian Tao, Zhu-An Xu