Soft Condensed Matter
Emergent Microrobotic Behavior of Active Flexicles in Complex Environments
Sophie Y. Lee, Philipp W.A. Schönhöfer and Sharon C. Glotzer
Collections of simple, self-propelled colloidal particles exhibit complex, emergent dynamical behavior, with promising applications in microrobotics. When confined within a deformable vesicle, self-propelled rods cluster and align, propelling the vesicle and inducing changes in the vesicle shape. We explore potential microrobotic capabilities of such vesicle-encapsulated particles, which form a composite particle system termed a `flexicle'. Using molecular dynamics simulations, we demonstrate that the
alignment of rods enables flexicles to locomote and respond adaptively to their physical environment. When encountering solid boundaries or obstacles, the rods reorient at the interface, triggering novel emergent behaviors such as crawling, corner-preferencing, wall climbing, and object-latching. These interactions and accompanying internal rod re-arrangement lead to spontaneous, temporary differentiation of the rods into `latchers' and `navigators'. This division of labor among the rods enables coordinated locomotion and environmental response. Our findings establish flexicles as a versatile platform for programmable, geometry-sensitive microrobotic behavior, offering a step toward autonomous colloidal robotics.
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Mesoscale and Nanoscale Physics
Impurity-induced topological decomposition
Tianxing Shi, Chuhang Zhang, Liang Jin et al. (+1 more)
Controlling topological phases is a central goal in
quantum materials and related fields, enabling applications such as robust transport and programmable edge states. Here we uncover a mechanism in which local on-site
impurities act as knobs to decompose global topological properties in discrete steps. In non-Hermitian
lattices with spectral winding
topology, we show that each
impurity sequentially reduces the winding number by one, which is directly manifested as a stepwise decomposition of quantized plateaus in the steady-state response. Based on this principle, we further develop a scheme that sequentially induces topological edge states under
impurity control, in a class of Hermitian topological systems constructed by doubling the non-Hermitian ones. Our findings reveal a general scheme to tune global topological properties with local perturbations, establishing a universal framework for
impurity-controlled topological phases and offering a foundation for future exploration of reconfigurable topological phenomena across diverse physical platforms.
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All authors Tianxing Shi, Chuhang Zhang, Liang Jin, Linhu Li
Statistical Mechanics · Cross-listed from quant-ph
Temporal Complexity Hierarchies in Solvable Quantum Many-Body Dynamics
He-Ran Wang, Ilya Vilkoviskiy and Dmitry A. Abanin
The influence
matrix (IM) provides a powerful framework for characterizing nonequilibrium
quantum many-body dynamics by encoding multitime correlations into tensor-network states. Understanding how its computational complexity relates to underlying dynamics is crucial for both theoretical insight and practical utility, yet remains largely unexplored despite a few case studies. Here, we address this question for a family of brickwork
quantum circuits ranging from integrable to chaotic regimes. Using tools from
geometric group theory, we identify three qualitatively distinct scalings of temporal
entanglement entropy, establishing a hierarchy of computational resources required for accurate tensor-network representations of the IM for these models. We further analyze the
memory structure of the IM and distinguish between classical and
quantum temporal correlations. In particular, for certain examples, we identify effectively classical IMs that admit an efficient Monte Carlo
algorithm for computing multitime correlations. In more generic settings without an explicit classical description of the IM, we introduce an operational measure of
quantum memory with an experimental protocol, and discuss examples exhibiting long-time genuinely
quantum correlations. Our results establish a new connection between
quantum many-body dynamics and group theory, providing fresh insights into the complexity of the IM and its intricate connection to the physical characteristics of the dynamics.
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Strongly Correlated Electrons
Intertwined Orders, Quantum Criticality and Skyrmions in Tunable Topological Bands
Xuepeng Wang, Johannes S. Hofmann and Debanjan Chowdhury
Skyrmions are emergent many-body excitations that lie at the heart of both multi-component
quantum Hall-like systems and deconfined
quantum criticality. In a companion article (X. Wang et al., arXiv:2507.22971), we studied a microscopic time-reversal symmetric model of tunable interacting Chern bands using numerically exact determinant
quantum Monte Carlo calculations, and presented evidence for the emergence of robust skyrmion excitations. These charged excitations emerge in the vicinity of a many-body
insulator at a commensurate filling of the Chern bands, and lead to the onset of superconductivity when doped away from the insulating phase. Here, we present
quantum Monte-Carlo results and a complementary field-theoretical analysis for the
quantum phase transition(s) that arise between the intertwined phases as a function of two distinct tuning parameters. Our numerical results are consistent with a single continuous
quantum phase transition between an insulating Chern antiferromagnet and a fully gapped
superconductor, with an emergent SO(5)
symmetry at the putative critical point, highly suggestive of deconfined
quantum (pseudo-)criticality. We also present a detailed comparison between the momentum-resolved spectral functions associated with the neutral collective modes, single electron and composite
spin-polaron excitations obtained using a combination of Monte-Carlo computations and a Bethe-Salpeter analysis built on top of the self-consistent Hartree-Fock calculation. We end with a brief outlook on some of the interesting open problems.
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Statistical Mechanics · Cross-listed from astro-ph.CO
Analytic Marginalization over Binary Variables in Physics Data
Marcus Högås and Edvard Mörtsell
In many data analyses, each measurement may come with a simple yes/no correction; for example, belonging to one of two populations or being contaminated or not. Ignoring such binary effects may bias the results, while accounting for them explicitly quickly becomes infeasible as each of the $N$ data points introduces an additional parameter, resulting in an exponentially growing number of possible configurations ($2^N$). We show that, under generic conditions, an exact treatment of these binary corrections leads to a mathematical form identical to the well-known Ising model from statistical physics. This connection opens up a powerful set of tools developed for the Ising model, enabling fast and accurate likelihood calculations. We present efficient approximation schemes with minimal computational cost and demonstrate their effectiveness in applications, including Type Ia
supernova calibration, where we show that the uncertainty in host-
galaxy mass classification has negligible impact on the inferred value of the Hubble constant.
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Other Condensed Matter
Power- and time-dependent equivalent circuit models for waveform-selective metasurfaces with varying electromagnetic responses to repeated pulses at the same frequency
Ryuho Miyamoto and Hiroki Wakatsuchi
Waveform-selective metasurfaces offer unprecedented control over electromagnetic waves on the basis of pulse width. However, existing
circuit models fail to capture the power-dependent behaviors of these metasurfaces, thereby limiting their use in practical applications. Here, for the first time, we present analytical equivalent
circuit models that accurately predict both power- and time-dependent responses by incorporating voltage-dependent diode resistance through the Maclaurin series and Wright omega functions. As a result, the variations in the input power and time domain are effectively predicted theoretically. Moreover, our concept is successfully extended to different types of waveform-selective metasurfaces and increasingly complex scenarios, including repeated pulses and nonresonant frequencies. Thus, our equivalent
circuit approach can readily explain and quantify the electromagnetic behaviors of waveform-selective metasurfaces. This strategy provides a high degree of control for addressing complex electromagnetic problems by leveraging pulse width as a tuning parameter, even at a fixed frequency.
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Disordered Systems and Neural Networks
Markov Inequality as a Tool for Linear-Scaling Estimation of Local Observables
H. P. Veiga, D. R. Pinheiro, J. P. Santos Pires et al. (+1 more)
We introduce a linear-scaling
stochastic method to compute real-space maps of any positive local spectral operator in a tight-binding model. By employing positive-definite
estimators, the sampling error at each site can be rigorously bounded relative to the mean via the Markov inequality, overcoming the lack of self-averaging and enabling accurate estimates even under strong spatial fluctuations. The approach extends to non-diagonal observables, such as local currents, through local
unitary transformations and its effectiveness is showcased by
benchmark calculations in the disordered two-dimensional (2D) $\pi$-flux model, where the LDoS and steady-state current maps are computed. This method will enable simulations of disorder-driven mesoscopic phenomena in realistically large
lattices and accelerate real-space self-consistent mean-field calculations.
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All authors H. P. Veiga, D. R. Pinheiro, J. P. Santos Pires, J. M. Viana Parente Lopes
Materials Science
The Piezochiral Effect
Z. Zeng, M. Först, M. Fechner et al. (+3 more)
Chirality is a pervasive property of matter that underpins many important phenomena across physics, chemistry and biology. Given its broad significance, the development of protocols for rational control of chirality in solid state systems is highly desirable, especially if this effect can be tuned continuously and in two directions. Yet, this goal has remained elusive due to the absence of a universal conjugate field that couples linearly to this structural order. Here, we introduce the piezochiral effect, which enables control of chirality through mechanical strain. We first show by
symmetry analysis that uniaxial strain induces chirality in a broad class of achiral
crystals that host fragments of opposite chirality within each unit
cell, an effect that has so far remained unrecognized. The strain-induced handedness can be tuned either by changing the strain direction or by switching between compressive and tensile strain. We experimentally verify this effect in AgGaS2, using measurements of the optical activity under strain. Our discovery establishes a new scheme for chirality control, with potential applications that range from spintronics to asymmetric catalysis, and enantioselective interactions in biosystems.
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All authors Z. Zeng, M. Först, M. Fechner, X. Deng, A. Cavalleri, P.G. Radaelli
Statistical Mechanics
Beyond Poisson: First-Passage Asymptotics of Renewal Shot Noise
Julien Brémont
The first-passage time (FPT) of a
stochastic signal to a threshold is a fundamental observable across physics, biology, and finance. While renewal shot noise is a canonical model for such signals, analytical results for its FPT have remained confined to the Poisson (Markovian) case, despite the prevalence of non-Poisson arrival statistics in applications from neuronal spiking to gene expression. We break this long-standing barrier by deriving the first universal asymptotic formula for the mean FPT $\langle T_b \rangle$ to reach level $b$ for renewal shot noise with general arrival statistics and exponential marks. Our central result is a closed-form expression that reveals precisely how general inter-arrival statistics impact the naive Arrhenius law. We show that the short-time behavior of the interarrival distribution dictates universal scaling corrections, ranging from stretched-exponential to algebraic, that can dramatically accelerate threshold crossing. Furthermore, we show analytically and confirm numerically that the full FPT distribution becomes exponential at large thresholds, implying that $\langle T_b \rangle$ provides a complete asymptotic characterization. Our work, enabled by a novel exact solution for the moments of the noise, establishes a general framework for analyzing extreme events in non-Markovian systems with relaxation.
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Soft Condensed Matter
Identification of 2D colloidal assemblies in images: a threshold processing method versus machine learning
L. T. Khusainova and K.S. Kolegov
This paper is devoted to the problem of identification of colloidal assemblies using the example of two-dimensional coatings (monolayer assemblies). Colloidal systems are used in various fields of science and technology, for example, in applications for photonics and functional coatings. The physical properties depend on the morphology of the structure of the colloidal assemblies. Therefore, effective identification of particle assemblies is of interest. The following classification is considered here: isolated particles, dimers, chains and clusters. We have studied and compared two identification methods: image threshold analysis using the OpenCV library and machine learning using the YOLOv8 model as an example. The features and current results of training a neural network model on a
dataset specially prepared for this work are described. A comparative characteristic of both methods is given. The best result was shown by the machine learning method (97% accuracy). The threshold processing method showed an accuracy of about 67%. The developed
algorithms and software modules may be useful to scientists and engineers working in the field of materials science in the future.
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Materials Science
Tailoring dispersion and evanescent modes in multimodal nonlocal lattices using positive-only interactions
Lucas Rouhi and Christophe Droz
Metamaterials derive their unconventional properties from engineered microstructures, with periodic
lattices providing a versatile framework for modeling wave propagation. Dispersion relations, obtained from Bloch-Floquet theory, govern how waves propagate, attenuate, or localize within such systems. Extending interactions beyond nearest neighbors, through nonlocality, substantially enriches the design space of band diagrams, enabling phenomena such as negative or zero group velocities, roton-like extrema, and band-gap localization. However, existing approaches to dispersion tailoring often rely on analytical formulations or
Fourier-based identifications, which become impractical for complex coupling mechanisms and offer limited control over physical constraints such as stiffness positivity. This work introduces a general interpolation-based framework for customizing dispersion relations in uniform nonlocal
lattices. Rather than reconstructing full dispersion curves, the method enforces prescribed frequency-wavenumber points as interpolation constraints, enabling localized and tunable control of wave behavior. The formulation is applied to both spring- and beam-interaction
lattices, and demonstrated on an Euler-Bernoulli beam model with adjustable nonlocal couplings. Through systematic parameter tuning, the framework enables the creation of rotons, the adjustment of group-velocity dispersion, and the design of evanescent waves with controlled exponential decay within band gaps, all while ensuring real, positive-only stiffness parameters and passive mechanical behavior. Altogether, this parametric interpolation strategy provides a physically consistent and computationally efficient route for engineering advanced phononic functionalities in periodic nonlocal systems.
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Materials Science
Zeeman Spectroscopy of Vacancy-Charge-Compensated Er3+ Sites in CaWO4 under Vector Magnetic Fields
Fabian Becker, Sudip KC, Lorenz J. J. Sauerzopf et al. (+4 more)
We present polarization-resolved optical absorption measurements on Er3+ ions in CaWO4 under vector
magnetic fields, focusing on charge-compensated sites arising from local Ca2+ vacancies. While the known axial Er3+ site displays a single symmetric Zeeman-split transition pattern consistent with S4
symmetry, two additional sites exhibit more complex spectral behavior, including sets of transitions that interchange under 90{\deg}
crystal rotations-evidence of reduced, rhombic-like
symmetry. From these polarization- and temperature-dependent spectra, we extract effective g-factors. Our findings are corroborated by electron paramagnetic resonance measurements and support a model of multiple inequivalent Ca2+ vacancies around Er3+ sites in the host
lattice. This detailed characterization contributes to understanding defect-engineered rare-earth sites for
quantum information applications.
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All authors Fabian Becker, Sudip KC, Lorenz J. J. Sauerzopf, Tim Schneider, Luis Risinger, Christian Schmid, Kai Müller
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Wide-field stroboscopic imaging of topologically protected phononic modes
Ilia Chernobrovkin, Maurice Debray, Frederik Holst Knudsen et al. (+5 more)
Imaging spatial mode profiles is important for understanding the behavior of mechanical resonators. The recent development of phononic
circuits has increased the demand for a fast imaging method based on principles of coherent detection. However, it becomes complicated to perform measurements on a large surface area. Here, we present a frequency-detuned collimated-beam interferometry measurement scheme with in-plane spatial resolution of about 6 um, which can provide information about the phase dynamics of the entire mechanical oscillation cycle on a time scale of a few seconds. We employ a stroboscopic pulse probing method to resolve high-frequency vibrational motion with a standard CMOS camera. We use this setup to image megahertz frequency resonant mode profiles present in a Valley-
Hall topological triangular cavity, over an area of more than 20 mm2. We relate the obtained data to numerical simulations of the topological edge modes to reveal the relation between backscattering and the mode profile distribution. The presented protocol can become a staple for characterizing mesoscopic mechanical resonators.
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All authors Ilia Chernobrovkin, Maurice Debray, Frederik Holst Knudsen, Thibault Capelle, Mads Bjerregaard Kristensen, Michael Pitts, Xiang Xi, Albert Schliesser
Strongly Correlated Electrons
Field-induced magnetic phase transition driven by a ground state level-crossing in CsErSe$_2$
Hope Whitelock, Allen O. Scheie, Marissa McMaster et al. (+12 more)
We report a comprehensive study of the low-temperature
magnetic properties of the insulating rare-earth triangular magnet CsErSe$_2$. We uncover a field-induced level crossing at the
crystal electric field (CEF) ground state, which gives rise to a first order phase transition as well as to distinctive
magnetic properties. This crossing is identified by the accurate determination of the single-ion
Hamiltonian, the reliability of which is substantially enhanced by field-dependent optical spectroscopy that directly tracks the Zeeman splittings of Kramers doublets. We also observe spontaneous
antiferromagnetic ordering in CsErSe$_2$ below $T_N \approx 110$ mK, and resolve the corresponding
magnetic structure using elastic
neutron scattering. We discuss how the rich
magnetic behavior of CsErSe$_2$ arises from the interplay of non-trivial field-dependent single-ion physics and spontaneous ordering, and highlight the implications of these results for understanding
magnetic phenomena across a wide range of insulating rare-earth magnets.
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All authors Hope Whitelock, Allen O. Scheie, Marissa McMaster, Ian A. Leahy, Li Xiang, Mykhaylo Ozerov, Dmitry Smirnov, Eun Sang Choi, C. dela Cruz, M. O. Ajeesh, Eliana S. Krakovsky, Daniel A. Rehn, Jie Xing, Athena S. Sefat, Minhyea Lee
Quantum Gases
Critical Exponent of Dynamical Quantum Phase Transition in One-Dimensional Bose-Hubbard Model in the Strong Interacting Limit
Jia Li and Yajiang Hao
We analytically investigated the dynamical
quantum phase transitions in the Bose-Hubbard model using the Loschmidt echo as an observable, revealing that after a quench, the global Loschmidt echo exhibits cusp singularities with a logarithmically divergent rate function near criticality and a critical exponent of zero. Through extensive calculations across various system sizes and initial states, we have demonstrated that in the strongly interacting regime, the critical singularity of dynamical
quantum phase transitions exhibits consistency across different model details and initial product states (charge-density wave states). Moreover, we find that modifying the harmonic potential well not only preserves the phase transition but also enables precise control over the transition timing.
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Superconductivity
ARPES of Bi2212 interpreted via a particle in a system of dynamic scatterers
Udomsilp Pinsook
In this work, I employ
parabolic cylinder functions to quantitatively describe the ARPES spectra of an over-doped Bi2212 across the temperature range 6 - 140K at the antinode k-point. These functions come from the solutions of a particle moving in a system of random scatterers. The parameters, i.e. the overall amplitude (A), the spectral coherence scale (C), and the energy shift (EG), are determined directly by fitting to experimental data. At 140K, the dominated feature of the ARPES spectrum resembles the solution of a particle moving in a one-dimensional random system. According to the present model, the electronic states of the over-doped Bi2212 at the antinode k-point can be viewed as a realization of the theory of a particle moving in dynamic scatterers in 1D with corrections from the ground state solutions at lower temperature.
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Soft Condensed Matter
Kinetic theory of emulsions with matter supply
Jacqueline Janssen, Frank Jülicher and Christoph A. Weber
In this work, we propose a theory for the kinetics of emulsions in which a continuous supply of matter feeds droplet growth. We consider cases where growth is either limited by bulk
diffusion or the transport through the droplets' interfaces. Our theory extends the Lifshitz-Slyozov-Wagner (LSW) theory by two types of matter supply, where either the supersaturation is maintained or the supply rate is constant. In emulsions with maintained supersaturation, we find a decoupling of droplets at all times, with the droplet size distribution narrowing in the
diffusion-limited regime and a drifting distribution of a fixed shape in the interface-resistance-limited case. In emulsions with a constant matter supply, there is a transition between narrowing and broadening in the
diffusion-limited regime, and the distribution is non-universal. For the interface-resistance-limited regime, there is no transition to narrowing, and we find a universal law governing coarsening kinetics that is valid for any constant matter supply. The average radius evolves according to a power law that is independent of the matter supply, and we find a closed-form expression for the droplet size distribution function. Our theory is relevant to biological systems, such as biomolecular condensates in living
cells, since droplet material is not conserved and the growth of small droplets is proposed to be interface-resistance-limited.
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Soft Condensed Matter
Swimming patterns of a multi-mode bacterial swimmer in fluid shear flow
Valeriia Muraveva, Agniva Datta, Jeungeun Park et al. (+5 more)
Bacterial swimming is well characterized in uniform
liquids at rest. The natural habitat of bacterial swimmers, however, is often dominated by moving fluids and interfaces, resulting in shear flows that may strongly alter bacterial
navigation strategies. Here, we study how fluid shear flow affects the swimming motility of the soil bacterium Pseudomonas putida, a bacterial swimmer that moves in a versatile pattern composed of three different swimming modes, where the flagella may push, pull, or wrap around the
cell body (multi-mode swimmer). We introduce a computer automated
cell tracking and swimming mode detection tool to show that shear induced
alignment depends on the swimming mode, while motility and proximity to surfaces counteract the
alignment effect. Moreover, filament wrapping becomes less efficient with increasing shear stress. Numerical simulations of realistic swimmer geometries complement our experimental results, providing more detailed mechanistic insights into movement patterns of bacterial swimmers in a shear flow.
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All authors Valeriia Muraveva, Agniva Datta, Jeungeun Park, Veronika Pfeifer, Yongsam Kim, Wanho Lee, Sookkyung Lim, Carsten Beta
Materials Science
Hexagonal InOI monolayer: a 2D phase-change material combining topological insulator states and piezoelectricity
Wenhui Wan, Xinyue Liu, Yanfeng Ge et al. (+2 more)
Two-dimensional (2D) phase-change materials (PCMs) with moderate transition barriers and distinctly contrasting properties are highly desirable for multifunctional devices, yet such systems remain scarce. Using first-principles calculations, we propose a hexagonal InOI monolayer as a promising 2D PCM. This material exhibits two distinct polymorphs: an energetically favorable T$^{\prime}$ phase and a metastable T phase, differentiated by iodine atom positions. The T$^{\prime}$-to-T structural phase transition features a moderate energy barrier $E_b$ of 72.1 meV per formula unit, facilitating reversible switching. Notably, strain engineering tailors the electronic transition, inducing either a metal-to-topological-
insulator or a metal-to-normal-
insulator transformation. Additionally, this phase transition modulates the piezoelectric response and shifts optical absorption from the infrared to the visible range. These multifunctional properties make 2D hexagonal InOI highly promising for applications in non-volatile
memory, low-contact-resistance spintronics, and optical switching devices.
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All authors Wenhui Wan, Xinyue Liu, Yanfeng Ge, Ziqang Li, Yong Liu
Mesoscale and Nanoscale Physics
Exciton-based sensing of remote electron correlations in 2D heterostructures
Tobias M. R. Wolf, Tian Xie, Chenhao Jin et al. (+1 more)
Many monolayer transition metal dichalcogenides, including MoS$_2$, MoSe$_2$, WS$_2$, and WSe$_2$, are direct bandgap two-dimensional (2D)
semiconductors with sharp optical resonances at excitonic bound state frequencies. Recent experiments have demonstrated that excitonic resonance frequencies in multilayer van der Waals stacks are altered by long-range Coulomb interactions with electrons in nearby but electrically isolated 2D materials. These modulations have been successfully used to detect transitions between distinct states of remote strongly correlated 2D electron fluids. In this Letter we provide a theory of these frequency shifts, enabling a more quantitative interpretation of excitonic-sensing experiments, and apply it as an example to WSe$_2$ that is proximate to
graphene bilayers and multilayers.
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All authors Tobias M. R. Wolf, Tian Xie, Chenhao Jin, Allan H. MacDonald
Materials Science
Examining the Spin Structure of Altermagnetic Candidate MnTe Grown with Near Ideal Stoichiometry
Qihua Zhang, Christopher J. Jensen, Alexander J. Grutter et al. (+11 more)
Altermagnets are a recently-discovered class of materials with
magnetic ordering that have a zero net magnetization and a momentum-dependent
spin splitting in their band structure, arising from a collinear
spin arrangement with alternating polarizations in the
crystal lattice. The nickeline-structured manganese telluride ({\alpha}-MnTe) is an attractive altermagnet candidate due to its predicted large
spin splitting energy and a transition temperature near 300K. In this work, we present a thorough investigation of the
spin structure of {\alpha}-MnTe thin films grown by molecular beam epitaxy with very high
crystal quality and low residual magnetization. The epitaxial {\alpha}-MnTe films have a full-width-at-half-maximum of 0.1{\deg} as measured by x-ray-diffraction rocking curves and a root-mean-square roughness below 1 nm.
Neutron diffraction measurements confirm the
antiferromagnetic order in the {\alpha}-MnTe film and show a Néel temperature of 307 K. Polarized
neutron reflectometry detects a vanishingly small net magnetization which may be confined to the MnTe/InP interface, highlighting the near-ideal stoichiometry in the sample. In vacuo angle resolved photoemission spectroscopy reveals that the bulk band spectrum of the MnTe films is consistent with the weak altermagnetic order as theoretically predicted and observed for the high
symmetry nodal plane in the center of the Brillouin zone. This study establishes optimized growth conditions for the synthesis of stoichiometric {\alpha}-MnTe thin films which exhibit exceptional structural and
magnetic ordering, thereby providing a robust platform for the precise characterization of their altermagnetic properties.
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All authors Qihua Zhang, Christopher J. Jensen, Alexander J. Grutter, Sandra Santhosh, William D. Ratcliff, Julie A. Borchers, Thomas W. Heitmann, Narendirakumar Narayanan, Timothy R. Charlton, Mingyu Yu, Ke Wang, Wesley Auker, Nitin Samarth, Stephanie Law
Soft Condensed Matter
Probing and modeling cell-cell communication in 2D biomimetic tissues
Cécile Marie Vincent, Sapna Ravindran, Alexis Michel Prevost et al. (+3 more)
In tissues,
cells in direct physical contact with each other can exchange ions or molecules via
protein clusters called gap junctions that form channels across the membranes of adjacent
cells. Here, we use a simplified biomimetic approach, coupled with theoretical modeling, to unravel the physical mechanisms controlling such transport. Tissues are mimicked with 2D hexagonal networks of monodisperse aqueous droplets connected by lipid membranes called Droplet Interface
Bilayers (DIBs), decorated with $\alpha$-Hemolysin ($\alpha$HL) transmembrane
proteins forming nanopores through heptamerization in the membrane. The
diffusion of calcein across 2D DIB networks is thoroughly studied using epifluorescence microscopy at various $\alpha$HL concentrations. The results are successfully confronted with a Continuous Time Random Walk model in hexagonal networks, with an average waiting time increasing nonlinearly with the concentration of pore monomers.
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All authors Cécile Marie Vincent, Sapna Ravindran, Alexis Michel Prevost, Léa-Laetitia Pontani, Olivier Bénichou, Elie Wandersman
Other Condensed Matter
An Experimental Validation of Reconfigurable Intelligent Surfaces Achieving Pulse Width-Modulated Singular Reflection Angles Without External Power Sources
Eisuke Omori, Kairi Takimoto, Atsuko Nagata et al. (+3 more)
In this study, we introduce a design concept that leverages pulse width variation to enable a reconfigurable intelligent surface (RIS) and to autonomously switch reflection properties between two angles without any active control system. Our RIS alters its beam pattern from a singular specular reflection to another unique singular anomalous reflection when the incoming waveform changes from a short pulse to a continuous wave, even at the same frequency. Unlike conventional RISs, our passive control mechanism eliminates the requirements of active components and precise symbol-level synchronization with the transmitting
antennas, reducing the system complexity level while offering dynamic material adaptability. We numerically show that the proposed RIS design is capable of varying the received magnitude of an incident wave by a factor of ten, which is also experimentally validated for the first time. Employing binary phase-shift keying (BPSK) modulation, we further report that the communication characteristics can be varied by 7 dB or more, which indicates that the proposed design is not limited to a single frequency component as long as the bandwidth of the given signal is covered by that of the RIS design. These results may present new opportunities for exploring and deploying pulse width-dependent RISs in practical scenarios involving next-generation communication systems.
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All authors Eisuke Omori, Kairi Takimoto, Atsuko Nagata, Ashif Fathnan, Shinya Sugiura, Hiroki Wakatsuchi
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Exciton and biexciton preparation via coherent swing-up excitation in a GaAs quantum dot embedded in micropillar cavity
Claudia Piccinini, Aleksander Rodek, Abdulmalik A. Madigawa et al. (+9 more)
Coherent control of
quantum emitters is essential for scalable
quantum photonic technologies. The recently proposed swing-up of
quantum emitter (SUPER) scheme allows efficient and coherent preparation of single
photons via off-resonant, red-detuned
laser pulses, simplifying
laser suppression and enhancing
photon collection. We present a systematic study of SUPER excitation applied to a single GaAs
quantum dot in a low-Q micropillar cavity. We perform a comparison of the key figures of merit against the well-established two-
photon excitation (TPE). Despite requiring higher excitation powers, SUPER achieves near-unity population inversion of the
exciton state ($\sim$95%) and high single-
photon purity ($g^{(2)}=0.03$) comparable to that under TPE, while also exhibiting a shortened decay time ($\sim$200 ps) reducing the time jitter in the
exciton population. A polarization-resolved analysis reveals that when both excitation and collection are aligned with one of the
exciton dipoles, SUPER results in polarized single-
photon emission, exceeding the resonant TPE saturation by a factor of 1.45. Under optimized excitation conditions, we also observe biexciton preparation via a distinct SUPER resonance, confirmed by the appearance of the biexciton emission line, constituting the first experimental demonstration of biexciton preparation using SUPER. These findings are in good agreement with a proposed four-level theoretical model that incorporates the biexciton state. We also report that a slight misalignment of
laser polarization induces an additional SUPER resonance that selectively populates the orthogonal
exciton dipole, without altering the nominal excitation polarization. This unexpected behavior reveals a new degree of freedom for coherent state preparation. Our findings establish the SUPER scheme as a versatile tool for state-selective
exciton and biexciton control.
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All authors Claudia Piccinini, Aleksander Rodek, Abdulmalik A. Madigawa, Ailton Garcia Jr., Saimon F. Covre da Silva, Martin A. Jacobsen, Luca Vannucci, Gregor Weihs, Armando Rastelli, Vikas Remesh, Niels Gregersen, Battulga Munkhbat
Materials Science
2D Excitonics with Atomically Thin Lateral Heterostructures
S. Shradha, R. Rosati, H. Lamsaadi et al. (+18 more)
Semiconducting transition metal dichalcogenides (TMDs), such as MoSe$_2$ and WSe$_2$, exhibit unique optical and electronic properties. Vertical stacking of layers of one or more TMDs, to create
heterostructures, has expanded the fields of moiré physics and twistronics. Bottom-up fabrication techniques, such as chemical vapor deposition, have advanced the creation of
heterostructures beyond what was possible with mechanical exfoliation and stacking. These techniques now enable the fabrication of lateral
heterostructures, where two or more monolayers are covalently bonded in the plane of their atoms. At their atomically sharp interfaces, lateral
heterostructures exhibit additional phenomena, such as the formation of charge-transfer
excitons, in which the electron and hole reside on opposite sides of the interface. Due to the energy landscape created by differences in the band structures of the constituent materials, unique effects such as unidirectional
exciton transport and excitonic
lensing can be observed in lateral
heterostructures. This review outlines recent progress in
exciton dynamics and spectroscopy of TMD-based lateral
heterostructures and offers an outlook on future developments in excitonics in this promising system.
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All authors S. Shradha, R. Rosati, H. Lamsaadi, J. Picker, I. Paradisanos, Md T. Hossain, L. Krelle, L. F. Oswald, N. Engel, D. I. Markina, K. Watanabe, T. Taniguchi, P. K. Sahoo, L. Lombez, X. Marie, P. Renucci, V. Paillard, J.-M. Poumirol, A. Turchanin, E. Malic, B. Urbaszek
Mesoscale and Nanoscale Physics
Spin filtering on demand via localized states in an atomic-scale resonant tunneling magnetic tunnel junction
Maciej Bazarnik and Anika Schlenhoff
Spin filtering and its back-action
spin transfer torque (STT) are key ingredients of latest spintronic devices based on
magnetic tunnel junctions (MTJs). Resonant tunneling (RT), implemented by design or occurring as parasitic effects, is known to crucially affect macroscopic device performance, but direct experimental access to its individual microscopic processes has remained difficult. Here we apply the RT scheme from MTJs to
spin-polarized scanning tunneling microscopy (SP-STM) for ultimate miniaturization obtained by addressing distinct sites on individual nanomagnets. Combined with energy selectivity, our experimental model set-up enables to study the
spin filtering capabilities of RT through an individual
spin-split
vacuum resonance state and of the corresponding STT exerted on the nanomagnet. We find, that the sign and magnitude of the STT follow the effective
spin-polarization of the resonance state, which, as we show, can by tailored on demand either by adjusting the applied bias or the current injection point on the nanostructure. We anticipate, that our atomic-scale RT-MTJ approach and the discovery of a versatile tunable
spin-filter at smallest scale will prove invaluable for studying and designing next generation MTJs potentially based on recently discovered 2D van-der-Waals magnets or altermagnets.
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Superconductivity
Optimal superconductivity in twisted bilayer WSe$_2$ where the Van Hove singularity crosses half-filling
Michał Zegrodnik, Waseem Akbar, Andrzej Biborski et al. (+1 more)
The recent discovery of unconventional superconductivity has pointed to twisted WSe$_2$
bilayer as a versatile platform for studying the correlated and topological phases of matter. Here we analyze the effect of the displacement field and electron interactions on the formation of a topological paired state in twisted WSe$_2$. Our approach is based on the effective single band $t$-$J$-$U$ model supplemented with intersite Coulomb interaction term and treated within the Gutzwiller approximation. We show that the superconducting phase is stabilized in a small range of displacement fields where the Van Hove singularity crosses half-filling, which is in qualitative agreement with recent experimental data. According to our analysis, such a circumstance comes as a result of a subtle interplay between the large density of states of the Van Hove singularity, in combination with the renormalization effects that appear in the weak-to-moderate correlations regime. The two factors create favorable conditions for the SC pairing only in a small area of the phase diagram.
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All authors Michał Zegrodnik, Waseem Akbar, Andrzej Biborski, Louk Rademaker
Other Condensed Matter
Suppressing excitations using quantum-Brachistochrone and nearest-neighbour interactions
S John Sharon Sandeep, Dibyajyoti Sahu and Suhas Gangadharaiah
We examine excitation suppression in the transverse-field Ising model (TFIM), where finite-time drive across a
quantum critical point is assisted by the presence of a time-dependent coupling parameter. While conventional counterdiabatic protocols are designed to eliminate excitations, they often require complex many-body terms that are difficult to realize experimentally. In contrast, our approach employs a local, time-dependent modulation of an existing coupling term in the
Hamiltonian. Within the framework of
quantum optimal control, we find that under a linear ramp of the transverse field, the optimal
evolution of the second parameter follows a non-monotonic trajectory. For the TFIM, this protocol yields higher fidelity and improved robustness against noise compared to several orders of approximate counterdiabatic driving. Furthermore, we provide an analytical demonstration of anti-Kibble-Zurek scaling in the presence of noise acting on either the transverse field or the longitudinal coupling. These results highlight the potential of this approach for developing simple, noise-resilient protocols for finite-time
quantum state preparation.
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Materials Science
Lossy phononic metamaterials for valley manipulation
Shunda Yin, Qiuyan Zhou, Yuxiang Xi et al. (+5 more)
Non-Hermitian physics characterized by complex band spectra has established a new paradigm in condensed matter systems and metamaterials. Recently, non-Hermitian gain and nonreciprocity are deliberately introduced to valley manipulation, leading to various phenomena beyond the Hermitian scenarios, such as the amplified topological whispering gallery modes as an acoustic
laser. In contrast, pure loss is inevitable in practice and generally regarded as a detrimental factor. Here, we reveal that the coupling loss can manipulate valley degrees of freedom in a phononic metamaterial. Three distinct valley-related effects, including valley-resolved nonreciprocity that functions as a valley filter, valley-dependent skin effects where bulk states from different valleys localize at opposite boundaries, and valley-projected edge states with boundary-dependent lifetimes that leads to an anomalous beam splitting, are demonstrated through theoretical analysis and airborne sound experiments. Owing to the easy preparation of loss, our findings shed light on both non-Hermitian and valley physics and may facilitate innovative applications of valley-related devices.
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All authors Shunda Yin, Qiuyan Zhou, Yuxiang Xi, Weiyin Deng, Wei Chen, Jiuyang Lu, Manzhu Ke, Zhengyou Liu
Mesoscale and Nanoscale Physics
Universal Thickness-Dependent Absorption in Solids at the Nanoscale: Anomalous Enhancement in the Ultrathin Limit
Bhumika Chauhan, Nikhil Singh, Subhrajit Dalai et al. (+5 more)
Through systematic experimental and theoretical studies of layer-thickness-dependent absorption in semiconducting MoSe$_2$ and WS$_2$ across the visible to near-infrared spectral range, we demonstrate a universal absorption behavior in solids at nanoscale thicknesses. With increasing thickness, a non-monotonic
evolution of absorption integrated over the measured spectral region is revealed which is accompanied by pronounced oscillatory features. This shows a strong deviation from the expected Beer-Lambert law. Below 10 nm, we observe a sharp anomalous increase in absorption, with deviations from Beer's law exceeding 50% in layered
semiconductors. Our conclusions hold irrespective of the presence of any optical resonances such as
excitons or plasmons within the spectral window. The observed behavior has origins in the electromagnetic interference effects taking place between the two surfaces of the thin
crystals. The present work on 2D
semiconductors is extendable to all kinds of solids such as conventional
semiconductors (e.g. Si, GaAs, GaN, InP), (semi) metals (e.g. Al, Ag, Au, c-HOPG) and 2D
magnetic materials (e.g. CrSBr and NiPS$_3$). Our results provide fundamental insights into light-matter interactions in solids at the nanoscale and are vital for optimally designing the new generation of absorption-based flexible optoelectronic devices.
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All authors Bhumika Chauhan, Nikhil Singh, Subhrajit Dalai, Abhisek Saidarsan, Sayantan Patra, Sourabh Jain, Aparna Deshpande, Ashish Arora