Soft Condensed Matter
Mixing of a binary passive particle system using smart active particles
Thomas Jacob, Siddhant Mohapatra, Rajalingam A et al. (+2 more)
Controlled activity of active entities interacting with a passive environment can generate emergent system-level phenomena, positioning such systems as promising platforms for potential downstream applications in targeted drug delivery, adaptive and reconfigurable materials, microfluidic transport and related fields. The present work aims to realise an optimal mixing of two segregated species of passive particles by introducing a small fraction of active particles (2% by composition) with adaptive and intelligent behaviour, directed by a trained Artificial Neural Network-based
agent. While conventional run-and-tumble particles can induce mixing in the system, the smart active particles demonstrate superior performance, achieving faster and more efficient mixing. Interestingly, an optimal mixing strategy doesn't involve a uniform dispersion of active particles in the domain, but rather limiting their motion to an eccentrically placed zone of activity, inducing a global rotational motion of the passive particles about the system centre. A transition in the directionality of the passive particles' motion is observed along the radius towards the centre, likening the active particles' motion to an ellipse-shaped void with a defined surface speed. Situated at the intersection of active matter and machine learning, this work highlights the potential of integrating adaptive learning frameworks into traditional active matter models.
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All authors Thomas Jacob, Siddhant Mohapatra, Rajalingam A, Sam Mathew, Pallab Sinha Mahapatra
Quantum Gases · Cross-listed from quant-ph
Higher symmetry breaking and non-reciprocity in a driven-dissipative Dicke model
Jacquelyn Ho, Yue-Hui Lu, Tai Xiang et al. (+3 more)
Higher
symmetries in interacting many-body systems often give rise to new phases and unexpected dynamical behavior. Here, we theoretically investigate a variant of the Dicke model with higher-order discrete
symmetry, resulting from complex-valued coupling coefficients between
quantum emitters and a bosonic mode. We propose a driven-dissipative realization of this model focusing on optomechanical response of a driven atom tweezer array comprised of $n$ sub-ensembles and placed within an optical cavity, with the phase of the driving field advancing stepwise between sub-ensembles. Examining stationary points and their dynamical stability, we identify a phase diagram for $n\geq 3$ with three distinctive features: a $\mathbb{Z}_n$ ($\mathbb{Z}_{2n}$)
symmetry-breaking superradiant phase for even (odd) $n$, a normal unbroken-
symmetry phase that is dynamically unstable due to non-reciprocal forces between emitters, and a first-order phase transition separating these phases. This $n$-phase Dicke model may be equivalently realized in a variety of optomechanical or opto-magnonic settings, where it can serve as a testbed for studying high-order
symmetry breaking and non-reciprocal interactions in open systems.
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All authors Jacquelyn Ho, Yue-Hui Lu, Tai Xiang, Tsai-Chen Lee, Zhenjie Yan, Dan M. Stamper-Kurn
Strongly Correlated Electrons
Novel family of near-room-temperature compensated itinerant pyrochlore ferrimagnets, $R{\mathrm{In}}{\mathrm{Co}}_{4}$ ($R=$ Dy-Tm)
T. Shiotani, T. Waki, Y. Tabata et al. (+2 more)
We successfully synthesized single
crystals of a series of C15b Laves phase compounds, $R{\mathrm{In}}{\mathrm{Co}}_{4}$ ($R=$ Dy-Tm), with Co-pyrochlore and $R$-fcc sublattices, and systematically studied their
magnetic properties via magnetometry measurements. These itinerant cubic compounds, with Curie temperatures above room temperature, show compensated ferrimagnetism featuring an
antiferromagnetic coupling between the two sublattices. From this series, ${\mathrm{DyInCo}}_{4}$ exhibits the highest $T_{\rm C}$ (= 368 K) and a near-room-temperature compensation point $T_{\rm cp}$ (= 295 K). $T_{\rm C}$ does not change drastically with the $R$ atom, whereas $T_{\rm cp}$ depends on the de Gennes factor of $R^{3+}$. Another magnetization anomaly is observed in all the compounds at low temperatures, which may be indicative of changes in the
lattice or
magnetic structure. The easy axis the ferrimagnetic moment of ${\mathrm{DyInCo}}_{4}$, ${\mathrm{ErInCo}}_{4}$, and ${\mathrm{TmInCo}}_{4}$ is found at $T =$ 5 K to be along the [001], [111] and [110] directions, respectively. However, the simple easy-axis or easy-plane ferrimagnetic picture cannot be applied to ${\mathrm{HoInCo}}_{4}$. These observations suggest that the $R$ sublattice determines
magnetic anisotropy and compensation, while the Co sublattice plays a role in strong
magnetic ordering. The high Curie temperature, together with the magnetization compensation point near room temperature, renders these itinerant pyrochlore magnets interesting for spintronic applications.
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All authors T. Shiotani, T. Waki, Y. Tabata, I. Kézsmárki, H. Nakamura
Statistical Mechanics · Cross-listed from cs.CL
Probing Geometry of Next Token Prediction Using Cumulant Expansion of the Softmax Entropy
Karthik Viswanathan and Sang Eon Park
We introduce a cumulant-expansion framework for quantifying how large
language models (LLMs) internalize higher-order statistical structure during next-
token prediction. By treating the softmax
entropy of each layer's logit distribution as a perturbation around its "center" distribution, we derive closed-form cumulant observables that isolate successively higher-order correlations. Empirically, we track these cumulants in GPT-2 and Pythia models on Pile-10K
prompts. (i) Structured
prompts exhibit a characteristic rise-and-plateau profile across layers, whereas
token-shuffled
prompts remain flat, revealing the dependence of the cumulant profile on meaningful context. (ii) During training, all cumulants increase monotonically before saturating, directly visualizing the model's progression from capturing variance to learning skew, kurtosis, and higher-order statistical structures. (iii) Mathematical
prompts show distinct cumulant signatures compared to general text, quantifying how models employ fundamentally different processing mechanisms for mathematical versus linguistic content. Together, these results establish cumulant analysis as a lightweight, mathematically grounded probe of feature-learning dynamics in high-dimensional neural networks.
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Mesoscale and Nanoscale Physics
Classification of Weyl point trajectories in multi-terminal Josephson junctions
Kento Takemura and Tomohiro Yokoyama
Topological protection is an attractive signature in both fundamental and applied researches because it provides an exotic and robust state. Multi-terminal Josephson junctions have recently been studied extensively owing to the emergence of topologically protected Weyl points without the need for topological materials. In this study, we examine the dynamic properties of Weyl points in multi-terminal Josephson junctions. The junctions are modulated by external parameters, such as electric gate voltage,
magnetic flux, bias voltage. The Weyl points are manipulated and draw trajectories accompanied by pair creation and annihilation. The trajectories form both closed loops and open lines. We classify these trajectories using the Chern number and the phase diagram.
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Quantum Gases · Cross-listed from quant-ph
Turning Down the Noise: Power-Law Decay and Temporal Phase Transitions
Lieuwe Bakker, Suvendu Barik, Vladimir Gritsev et al. (+1 more)
We determine the late-time dynamics of a generic
spin ensemble with inhomogeneous broadening - equivalently,
qubits with arbitrary Zeeman splittings - coupled to a dissipative environment with strength decreasing as $1/t$. The approach to the steady state follows a power law, reflecting the interplay between
Hamiltonian dynamics and vanishing dissipation. The decay exponents vary non-analytically with the ramp rate, exhibiting a cusp singularity, and $n$-point correlation functions factorize into one- and two-point contributions. Our exact solution anchors a universality class of open
quantum systems with explicitly time-dependent dissipation.
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All authors Lieuwe Bakker, Suvendu Barik, Vladimir Gritsev, Emil A. Yuzbashyan
Mesoscale and Nanoscale Physics
Optical conductivity and band gap in the double-Weyl candidate SrSi2 at ambient pressure
L. Z. Maulana, A. A. Tsirlin, E. Uykur et al. (+4 more)
We probe the possible double-Weyl state in cubic SrSi2 using optical spectroscopy. The complex optical conductivity was measured in a frequency range from 70 to 22 000 cm-1 at temperatures down to 10 K at ambient pressure. The optical response of SrSi2 can be well separated into the intraband (free carriers) and interband contributions. Additionally, four infrared-active
phonons are detected. As follows from the optical spectra, the free-carrier density decreases with decreasing temperature, consistent with an activation behaviour. Experimental interband conductivity juxtaposed with ab initio calculations shows that conventional density-functional theory fails to describe the electronic structure of SrSi2 in the vicinity of the
Fermi level. A semi-local exchange-correlation potential allows a much better agreement with the experiment, resulting in the trivial (gapped) band structure of SrSi2. The direct gap estimated from the measurements is approximately 40 meV.
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All authors L. Z. Maulana, A. A. Tsirlin, E. Uykur, Y. Saito, M. Dressel, M. Imai, A. V. Pronin
Statistical Mechanics · Cross-listed from quant-ph
Operational Quasiprobability in Quantum Thermodynamics: Work Extraction by Coherence and Non-joint Measurability
Jeongwoo Jae, Junghee Ryu and Hoon Ryu
We employ the operational quasiprobability (OQ) as a work distribution, which reproduces the Jarzynski equality and yields the average work consistent with the classical definition. The OQ distribution can be experimentally implemented through the end-point measurement and the two-point measurement scheme. Using this framework, we demonstrate the explicit contribution of coherence to the fluctuation, the average, and the second moment of work. In a two-level system, we show that non-joint measurability, a generalized notion of measurement incompatibility, can increase the amount of extractable work beyond the classical bound imposed by jointly measurable measurements. We further prove that the real part of Kirkwood-Dirac quasiprobability (KDQ) and the OQ are equivalent in two-level systems, and they are nonnegative for binary unbiased measurements if and only if the measurements are jointly measurable. In a three-level Nitrogen-vacancy center system, the OQ and the KDQ exhibit different amounts of negativities while enabling the same work extraction, implying that the magnitude of negativity is not a faithful indicator of nonclassical work. These results highlight that coherence and non-joint measurability play fundamental roles in the enhancement of work.
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Soft Condensed Matter
Self-induced buckling in hollow microgels
Leah Rank and Emanuela Zaccarelli
Hollow microgels are elastic
polymer shells easily realizable in experiments. Recent works have shown the emergence of buckling events in dilute hollow microgels under the effect of an added osmotic pressure. Here, we perform large-scale simulations to show that these microgels at high enough packing fractions undergo spontaneous
symmetry-breaking deformations ranging from single large dents to multiple indentations, even in the absence of any externally applied stress. This self-induced buckling phenomenon is thus solely driven by interparticle crowding. We construct a phase diagram inspired by vesicle shape theories, mapping local
curvature metrics as a function of the reduced volume, to quantify these findings, and we also propose ways to observe the occurrence of buckling in experiments. The present results thus rationalize the deformations occurring in suspensions of micro- and nano-scale elastic shells, offering a synthetic analogue to biological ones and allowing direct control on buckling instabilities for potential applications. Beyond materials design, these insights may also help to describe shape regulation in natural systems such as
cells and vesicles, where similar deformations are observed.
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Statistical Mechanics
Interplay of order and disorder in two-dimensional critical systems with mixed boundary conditions
E.Eisenriegler
In
spin systems such as the Ising model, the local order and disorder can be characterized by the order-parameter and energy density profiles $\langle \sigma ({\bf r}_1) \rangle$ and $\langle \epsilon ({\bf r}_2) \rangle$, respectively. Does increasing the order at ${\bf r}_1$ always decrease the disorder at ${\bf r}_2$? Does increasing the disorder at ${\bf r}_2$ always decrease the order at ${\bf r}_1$? The answer to these questions is contained in the cumulant response function $\langle\sigma ({\bf r}_1) \, \epsilon ({\bf r}_2) \rangle^{(\rm cum)}$. This correlation function vanishes in the unbounded bulk but not in systems with fixed-
spin boundary conditions. Using the universal operator-product expansion of $\sigma ({\bf r}_1) \, \epsilon ({\bf r}_2)$ and exact results for the Ising model, we analyze $\langle\sigma ({\bf r}_1) \, \epsilon ({\bf r}_2) \rangle^{(\rm cum)}$ in two-dimensional critical systems defined on the $x-y$ plane with mixed $+$ and $-$ boundary conditions. Particularly interesting behavior is found when either of the operators $\sigma$ or $\epsilon$ is located on a “zero line" in the $x-y$ plane, along which $\langle\sigma ({\bf r})\rangle$ vanishes. Results for half-plane, triangular, and rectangular geometries are presented.
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Superconductivity
Variation Monte Carlo Study on the bilayer $t-J_{\parallel}-J_{\perp}$ model for La$_3$Ni$_2$O$_7$
Zeyu Chen, Yu-Bo Liu and Fan Yang
The discovery of high-temperature superconductivity (HTSC) in La$_3$Ni$_2$O$_7$ has aroused significant interest in exploring the pairing mechanism. Previous studies have proposed an effective d$_{x^2-y^2}$-orbital
bilayer $t-J_{\parallel}-J_{\perp}$ model, in which the electrons of the d$_{x^2-y^2}$ orbital are charge carriers, which are subject to the intralayer
antiferromagnetic (AFM) superexchange $J_{\parallel}$ and the large interlayer AFM superexchange $J_{\perp}\approx 2J_{\parallel}$, with the latter transferred from the nearly half-filled and hence localized $d_{z^2}$ orbital through the strong Hund's rule coupling. Here we study this model by the variational Monte Carlo (VMC) simulation and find a dominant interlayer s-wave pairing, in which the SC order parameters have a drastic improvement compared with those of the mean field (MF) type of theories. In real materials, the Hund's coupling is finite, leading to reduced $J_{\perp}$, dictating that the MF-type theories have difficulty explaining the HTSC. However, our VMC calculations find that even for effective $J_{\perp}$ as weak as $J_{\perp}=J_{\parallel}$, the interlayer pairing is still considerably large and can be compared with the $T_c$ observed in experiments, which is very weak in MF-type theories. This result indicates the important role of the Gutzwiller projection in improving the $T_c$, which is ignored in the MF-type theories. In addition, our results show that suppressed interlayer hopping can promote interlayer pairing, which is consistent with the fact that the interlayer hopping of the d$_{x^2-y^2}$ orbital in La$_3$Ni$_2$O$_7$ is very weak. Our research offers a new perspective for understanding the pairing mechanism of
bilayer nickelates and provides a reference for recent ultra-cold atom experiments in mixed-dimensional systems.
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Materials Science · Cross-listed from physics.optics
Quantum Emission in Monolayer WSe2 Transferred onto InP Nanowires
Palwinder Singh, Jasleen Kaur Jagde, Megha Jain et al. (+10 more)
Localized
quantum emitters in transition-metal dichalcogenides (TMDs) have recently emerged as solid-state candidates for on-demand sources of single
photons. Due to the role of strain in the site-selective creation of TMD emitters, their hybrid integration into photonic structures such as cavities and waveguides is possible using pick-and-place methods. Here we investigate
quantum emission from a hybrid structure consisting of a monolayer of WSe2 interfaced with horizontally aligned InP nanowires (NWs). Our experiments reveal multiple narrow and bright emission peaks in the 715-785 nm spectral range and g(2)(0) as low as 0.049, indicating strong antibunching and good single
photon purity. The faceted nature of III-V NWs provides unique opportunities for strain engineering, including the potential for placement of emitters on the top surface for optimal coupling. Our findings pave the way for realizing hybrid
quantum light sources for integrated
quantum photonics that could combine III-V
quantum dots with TMD emitters into a single platform.
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All authors Palwinder Singh, Jasleen Kaur Jagde, Megha Jain, Edith Yeung, David B. Northeast, Simona Moisa, Seid J. Mohammed, Jean Lapointe, Una Rajnis, Annika Kienast, Philip J. Poole, Dan Dalacu, Kimberley C. Hall
Materials Science
Longitudinal transport spin polarization of spin degenerate antiferromagnets
Meng Zhu, Jianting Dong, Xinlu Li et al. (+4 more)
A vital goal in spintronics is the efficient electrical generation of
spin currents, a pursuit that has recently focused on using antiferromagnets (AFMs) as
spin current sources. It has been demonstrated that antiferromagnets with broken PT
symmetry (parity + time reversal) can efficiently generate longitudinal and transverse
spin currents. At the same time, it has been generally thought that antiferromagnets with PT
symmetry (PT-AFMs) forbid the longitudinal
spin polarization due to their
spin-degenerate band structure. Here, in contrast to this common expectation, we show, using theoretical analysis based on
magnetic point group
symmetry, that most PT-AFMs can generate longitudinal
spin currents due to
spin-orbit coupling. Using density-functional theory, we calculate the longitudinal
spin conductivity of representative PT-AFMs, L10-MnPt and Mn2Au, and show that its magnitude is comparable to that of their PT-broken counterparts. Our
symmetry-enabled classification of antiferromagnets and theoretical results for the longitudinal
spin conductivity in representative PT-AFMs expands our understanding of
spin transport and shows the possibility of robust
spin-current generation in a broad range of
spin-degenerate antiferromagnets.
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All authors Meng Zhu, Jianting Dong, Xinlu Li, Jiahao Shentu, Yizhuo Song, Evgeny Y. Tsymbal, Jia Zhang
Materials Science
Dynamic breaking of axial symmetry of acoustic waves in crystals as the origin of nonlinear elasticity and chaos: Analytical model and MD simulations
Zbigniew Kozioł
A Chain of Springs and Masses (CSM) model is used in the interpretation of molecular dynamics (MD) simulations of movement of atoms in orientated FCC
crystals. A force of dynamic origin is found that is perpendicular to the direction of the external shear pressure. It is proportional to the square of the applied pressure; It causes breaking of axial
symmetry for propagation of transverse acoustic waves. It leads to a non-linear elastic response of
crystals and to chaotic patterns in the motion of atoms. We provide an analytical derivation of an effective atomistic 3D potential for interaction between crystallographic layers. The potential is found to possess a component that has an anharmonic threefold axial
symmetry around one direction. It reduces to the Hénon-Heinen potential in a 2D cross-section, leading to mathematically rich, complex dynamic features. Results of simulation predict displacements of atoms that are inconsistent with the static theory of elasticity that may have been overlooked in experiments.
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Statistical Mechanics · Cross-listed from quant-ph
Clifford Circuits Augmented Grassmann Matrix Product States
Atis Yosprakob, Wei-Lin Tu, Tsuyoshi Okubo et al. (+2 more)
Recent progress in combining Clifford
circuits with tensor-network (TN) methods has shown that local Clifford disentanglers can reduce bipartite
entanglement across TN bonds prior to tensor compression, thereby improving the efficiency of TN simulations. In this work, we embed local Clifford disentanglers in the Grassmann-tensor
language to define a Clifford-augmented Grassmann
matrix product state (CAGMPS) ansatz, and develop a density-
matrix renormalization group (DMRG) framework based on this ansatz while preserving locality and
fermion-parity structure. We
benchmark the resulting CAGMPS–DMRG method on representative fermionic
lattice systems, including the tight-binding, $t$-$V$, and $t$-$V$-$V'$ models. In all cases, Clifford augmentation systematically suppresses bipartite
entanglement and improves the accuracy of the ground-state energy at a fixed bond dimension. We further show that the Grassmann-evenness condition, together with equivalence under entangling action, restricts the relevant two-site Clifford candidates to 12 inequivalent representatives, enabling a more economical disentangling search than approaches based on the standard two-
qubit Clifford gate set. Our results suggest that the CAGMPS–DMRG method provides a scalable and efficient variational tool for strongly correlated fermionic systems.
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All authors Atis Yosprakob, Wei-Lin Tu, Tsuyoshi Okubo, Kouichi Okunishi, Donghoon Kim
Strongly Correlated Electrons
More bridging ligands activate direct exchange: the case of anisotropic Kitaev effective magnetic interactions
Pritam Bhattacharyya, Nikolay A. Bogdanov and Liviu Hozoi
A magnet is a collection of
magnetic moments. How those interact is determined by what lies in between. In transition-metal and rare-earth
magnetic compounds, the configuration of the ligands around each
magnetic center and the connectivity of the ligand cages are therefore pivotal – for example, the mutual interaction of
magnetic species connected through one single ligand is qualitatively different from the case of two bridging anions. Two bridging ligands are encountered in Kitaev magnets. The latter represent one of the revelations of the 21st century in magnetism research: they feature highly anisotropic intersite couplings with seemingly counterintuitive directional dependence for adjacent pairs of
magnetic sites and unique
quantum spin-
liquid ground states that can be described analytically. Current scenarios for the occurrence of pair-dependent
magnetic interactions as proposed by Kitaev rely on $indirect$ exchange mechanisms based on intersite electron hopping. Analyzing the wavefunctions of Kitaev
magnetic bonds at both single- and multi-configuration levels, we find however that $direct$, Coulomb exchange may be at least as important, in 5$d$ and 4$d$ $t_{2g}^5$, 3$d$ $t_{2g}^5e_g^2$, and even rare-earth 4$f^1$ Kitaev-Heisenberg magnets. Our study provides concept clarification in Kitaev magnetism research and the essential reference points for reliable computational investigation of how novel
magnetic ground states can be engineered in Kitaev, Kitaev-Heisenberg, and Heisenberg edge-sharing systems.
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Quantum Gases
Right-eigenstate-based approach to non-Hermitian superfluidity with two-body loss
Xuezhu Liu, Ming Lu and Haiwen Liu
We theoretically explore a non-Hermitian superfluid model with complex-valued interaction, inspired by two-body loss stemming from inelastic scattering observed in ultracold atomic experiments. Utilizing both the right-eigenstate-based mean-field theory and its biorthogonal counterpart, we study the properties of the system. Notably, the right-eigenstate-based framework produces smooth and continuous solutions, in stark contrast to the absence of nontrivial solutions and the abrupt discontinuities observed in the biorthogonal-eigenstate-based framework under moderate dissipation. In addition, the lower condensation energy obtained in the former framework suggests its superior suitability for describing this system. Furthermore, we explore the impact of backscattering, a crucial factor in realistic systems. Our analysis reveals that, facilitated by two-body loss, even moderate backscattering destabilizes the superfluid state. Sufficiently strong backscattering completely destroys it, highlighting a key mechanism for the fragility of this non-Hermitian
quantum phase.
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Strongly Correlated Electrons
Ground state and excitations of quasiperiodic 1D narrow-band moiré systems: a mean field approach
Nicolau Sobrosa, Miguel Gonçalves, Bruno Amorim et al. (+2 more)
We demonstrate that a mean field approximation can be confidently employed in quasiperiodic moiré systems to treat interactions and quasiperiodicity on equal footing. We obtain the mean field phase diagram for an illustrative one-dimensional moiré system that exhibits narrow bands and a regime with non-interacting multifractal critical states. By systematically comparing our findings with existing exact results, we identify the regimes where the mean field approximation provides an accurate description. Interestingly, in the critical regime, we obtain a quasifractal charge density wave, consistent with the exact results. To complement this study, we employ a real-space implementation of the time-dependent Hartree-Fock, enabling the computation of the excitation spectrum and response functions at the RPA level. These findings indicate that a mean field approximation to treat systems hosting multifractal critical states, as found in two-dimensional quasiperiodic moiré systems, is an appropriate methodology.
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All authors Nicolau Sobrosa, Miguel Gonçalves, Bruno Amorim, Eduardo V. Castro, Pedro Ribeiro
Mesoscale and Nanoscale Physics
Quantum Linear Magnetoresistance: A Modern Perspective
Shuai Li and Huichao Wang
Magnetoresistance is a powerful probe for characterizing the intrinsic physics embedded in materials. Among its various manifestations, linear magnetoresistance has a long history and continues attracting research interest. In contemporary studies, a clear understanding of the magnetoresistance character of
quantum origin is more crucial than ever for the study of emerging materials. In this perspective, we examine the linear magnetoresistance of
quantum mechanism, from its theoretical basis to experimental studies, and discuss open questions and promising future research directions in this field.
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Materials Science
Direct observation of band structure modifications from monolayer WSe2 to Janus WSSe
Masato Sakano, Shunsuke Akatsuka, Takato Yamamoto et al. (+19 more)
Janus monolayer transition metal dichalcogenides (TMDs), created by post-growth substitution of the top chalcogen layer, represent a new direction for engineering 2D
crystal properties. However, their rapid ambient degradation and the difficulty of obtaining large-area monolayer samples have limited the available experimental probes, leaving their detailed electronic structure near the
Fermi level largely unexplored. In this work, by performing micro-focused angle-resolved photoemission spectroscopy ({\mu}-ARPES) on an identical sample transformed from monolayer WSe2 to Janus WSSe via a H2
plasma-assisted chalcogen-exchange method, we reveal the
evolution of its electronic band structure. We observe ARPES signature consistent with the Rashba-type
spin splitting due to broken horizontal mirror
symmetry, and a significant upward shift of the highest valence band at the {\Gamma}-point by approximately 160 meV. These direct observations clarify the key electronic modifications that govern the material's properties and provide a pathway for band engineering in Janus TMDs.
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All authors Masato Sakano, Shunsuke Akatsuka, Takato Yamamoto, Tianyishan Sun, Dingkun Bi, Hiroto Ogura, Naoya Yamaguchi, Fumiyuki Ishii, Natsuki Mitsuishi, Kenji Watanabe, Takashi Taniguchi, Miho Kitamura, Koji Horiba, Kenichi Ozawa, Katsuaki Sugawara, Seigo Souma, Takafumi Sato, Yuta Seo, Satoru Masubuchi, Tomoki Machida, Toshiaki Kato, Kyoko Ishizaka
Statistical Mechanics
Strong-coupling phases of conserved growth models are crumpled
Debayan Jana and Abhik Basu
We show that stochastically driven nonequilibrium conserved growth models admit generic strong coupling phases for sufficiently strong nonlocal chemical potentials underlying the dynamics. The models exhibit generic roughening transitions between perturbatively accessible weak coupling phases satisfying an exact relation between the scaling exponents in all dimensions $d$, and strong coupling phases. In dimensions at or below the critical dimension $d_c$, the latter phases are unstable and argued to be crumpled, and thus distinct from the well-known strong coupling rough phase of the Kardar-Parisi-Zhang equation in dimensions $d\geq 2$. At $d_c$, conventional spatiotemporal scaling in the weak coupling phase is logarithmically modulated and are exactly obtained.
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Materials Science · Cross-listed from physics.optics
Binary $ZnSe:Fe^{2+}$ and ternary $ZnMgSe:Fe^{2+}$ optical crystals for mid-IR applications
Sergei V. Naydenov, Oleksii K. Kapustnyk, Igor M. Pritula et al. (+3 more)
In this study, binary $ZnSe:Fe^{2+}$
crystals and ternary $Zn_{1-x}Mg_{x}Se:Fe^{2+}$
crystals $(0 < x < 0.6)$ were grown by the vertical Bridgman method in graphite crucibles under high argon pressure. A comparative characterization of the structural, energetic, and optical parameters of the obtained
crystals was performed. Theoretical explanations of the observed experimental characteristics, including the specific red-shift of the absorption and emission spectra with increasing solid-solution concentration, are provided. These results could be useful for the development of new
laser media based on simple and complex AIIBVI
crystals and for targeted engineering of their optical properties.
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All authors Sergei V. Naydenov, Oleksii K. Kapustnyk, Igor M. Pritula, Dmitro S. Sofronov, Igor S. Terzin, Nazar O. Kovalenko
Statistical Mechanics
Dynamics of the Kac Ring Model with switching scatterers
Leonid A. Bunimovich, Emilio N. M. Cirillo, Matteo Colangeli et al. (+1 more)
We introduce a generalized version of the Kac ring model in which particles are of two types, black and white. Black particles modify the environment through which all particles move, thereby inducing indirect and potentially long-range interactions among them. Unlike the inert scatterers of Kac's original model, the scatterers in our setting possess internal states that change upon interaction with black particles and can be interpreted as energy levels of the environment. This makes the model self-consistent, as it incorporates a form of particle interactions, mediated by the environment, that drives the system toward some kind of stationary state. Although indirect and long-range interactions do not necessarily promote thermodynamic states, interactions are necessary for energy to be shared among the elementary constituents of matter, enabling the establishment of equipartition, which is a prerequisite for defining temperature. Therefore, our model is one step forward in this direction, elucidating the role of interactions and energy exchange. We prove that any initial state of the system converges to a time periodic state (i.e. a phase space orbit) and describe basins of attraction for some of such asymptotic periodic states.
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All authors Leonid A. Bunimovich, Emilio N. M. Cirillo, Matteo Colangeli, Lamberto Rondoni
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Approaching the scaling limit of transport through lattices with dephasing
Subhajit Sarkar, Gabriela Wójtowicz, Bartłomiej Gardas et al. (+2 more)
We examine the stationary–state equations for
lattices with generalized Markovian dephasing and relaxation. When the
Hamiltonian is quadratic, the single–particle correlation
matrix has a closed system of equations even in the presence of these two processes. The resulting equations have a vectorized form related to, but distinct from, Lyapunov's equation. We present an efficient solution that helps to achieve the scaling limit, e.g., of the current decay with
lattice length. As an example, we study the super–diffusive–to–diffusive transition in a
lattice with long–range hopping and dephasing. The approach enables calculations with up to $10^4$ sites, representing an increase of $10$ to $40$ times over prior studies. This enables a more precise extraction of the
diffusion exponent, enhances agreement with theoretical results, and supports the presence of a phase transition. There is a wide range of problems that have Markovian relaxation, noise, and driving. They include
quantum networks for machine–learning–based classification and extended reservoir approaches (ERAs) for transport. The results here will be useful for these classes of problems.
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All authors Subhajit Sarkar, Gabriela Wójtowicz, Bartłomiej Gardas, Marek M. Rams, Michael Zwolak
Other Condensed Matter
Operator dependence and robustness of spacetime-localized response in a quantum critical spin chain
Daichi Imagawa, Keiju Murata and Daisuke Yamamoto
We investigate the phenomenon of spacetime-localized response in a
quantum critical
spin system, with particular
attention to how it depends on the spatial profile and operator content of the applied perturbation, as well as its robustness against increase of amplitude and temporal discretization. Motivated by recent theoretical proposals linking such response patterns to the anti-de Sitter/conformal field theory correspondence, we numerically analyze the real-time dynamics of the one-dimensional transverse-field Ising model at criticality using the time-evolving block decimation
algorithm. We find that sharply localized and periodically recurring responses emerge only for specific types of perturbations, namely those that correspond to local density fields in the continuum limit. In contrast, perturbations involving other
spin components produce conventional propagating excitations without localization. Furthermore, we demonstrate that the response remains qualitatively robust when the time-dependent perturbation is approximated by a piecewise-linear function, highlighting the practical relevance of our findings for
quantum simulation platforms with limited temporal resolution. Our results clarify the operator dependence of emergent bulk-like dynamics in critical
spin chains and offer guidance for probing
holographic physics in experimental settings.
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Materials Science
Atomistic Machine Learning with Irreducible Cartesian Natural Tensors
Qun Chen, A. S. L. Subrahmanyam Pattamatta, Boyu Wang et al. (+2 more)
Atomistic machine learning is a powerful tool for accurate and efficient investigation of material behavior at the atomic scale. While attempts have been made to construct models directly within Cartesian space, they face challenges in providing a systematic framework based on irreducible representations - a core feature of widely used spherical models. Here we propose Cartesian Natural Tensor Networks to overcome these limitations and thus offer a general,
symmetry-preserving framework for atomistic machine learning. We present a theory of irreducible representations using Cartesian natural tensors, comprising their construction, their products, and a systematic scheme to decompose and reconstruct high-rank physical tensors. Leveraging this machinery, we develop equivariant machine learning interatomic potentials for materials and molecular systems with performance on par with leading spherical models. It further captures accurate structure-property relationships for tensorial quantities ranging from low-rank dipole moments to high-rank tensors with complex
symmetries, such as the elastic constant tensor.
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All authors Qun Chen, A. S. L. Subrahmanyam Pattamatta, Boyu Wang, David J. Srolovitz, Mingjian Wen
Mesoscale and Nanoscale Physics
Can out-of-equilibrium linear response reveal anyonic statistics?
Gu Zhang, Igor Gornyi and Yuval Gefen
Determination of the anyonic statistical braiding phase has relied on either Aharonov-Bohm inter- ference experiments or cross-correlations measured in
collider platforms. Here we consider
collider setups, supporting stationary far-from-
equilibrium anyonic beams, characterized by an effective chemical potential and an effective temperature, which carry universal information about the ele- mentary charge and the statistical braiding phase. We develop an out-of-
equilibrium linear response theory designed to describe charge and thermal
quantum transport under deviations from this ef- fective
equilibrium (unlike linear response designed to describe transport near genuine
equilibrium). Our effective linear-response transport coefficients directly reflect the fractional charge and statistics of the anyons involved, avoiding the need to measure higher-order current correlations. Moreover, the emergence of finite thermoelectric (Peltier and Seebeck) coefficients signifies the presence of real anyon collisions (as opposed to virtual braiding in the time domain), intimately associated with the breaking of a characteristic particle-hole
symmetry specific to anyonic gases.
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Mesoscale and Nanoscale Physics
Fractional quantum Hall state at $\nu = 1/2$ with energy gap up to 6 K, and possible transition from one- to two-component state
Siddharth Kumar Singh, Chengyu Wang, Adbhut Gupta et al. (+3 more)
The fractional
quantum Hall state (FQHS) observed in the lowest Landau level at filling factor $\nu=1/2$ in wide
quantum wells has been enigmatic for decades because the two-dimensional electron system (2DES) has a
bilayer charge distribution but with significant interlayer tunneling. Of particular interest is whether the 1/2 FQHS in this system has a one-component (1C) or two-component (2C) origin; these are typically identified as the Pfaffian (non-Abelian) or the $\Psi_{331}$ (Abelian) FQHSs, respectively. We report here our experimental study of the
evolution of the correlated states of an ultrahigh-quality 2DES confined to a 72.5-nm-wide GaAs
quantum well. At the lowest densities, the 2DES displays only odd-denominator FQHSs, and the ground state at $\nu = 1/2$ is a composite
fermion Fermi sea. As the density is increased, a FQHS emerges at $\nu = 1/2$, and becomes very strong. In a finite density range where the 1/2 FQHS is strongest, we also observe its daughter FQHSs at $\nu = 8/17$ and 7/13, consistent with the theoretically expected daughter states of a Pfaffian 1/2 FQHS. At the highest densities, the 2DES becomes 2C, signaled by the emergence of a
bilayer Wigner
crystal state and the transitions of FQHSs flanking $\nu=1/2$. The 1/2 FQHS remains robust near this transition and, notably, its charge transport energy gap exhibits an upward cusp with a maximum value of about 6 K on the 1C side of the transition; this is the largest gap reported for any even-denominator FQHS. Our observation of the transition of the 2DES ground states near $\nu=1/2$ to 2C states at high densities, and our measurements of the robustness of the 1/2 FQHS against charge distribution asymmetry, suggest that the 1/2 FQHS also makes a transition from 1C to 2C. Such a transition from a non-Abelian to Abelian state can open avenues for topological
quantum information and
quantum criticality.
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All authors Siddharth Kumar Singh, Chengyu Wang, Adbhut Gupta, Kirk W. Baldwin, Loren N. Pfeiffer, Mansour Shayegan
Mesoscale and Nanoscale Physics
Coupling a $^{73}$Ge nuclear spin to an electrostatically defined quantum dot
Paul Steinacker, Gauri Goenka, Rocky Yue Su et al. (+17 more)
Single
nuclear spins in silicon are a promising resource for
quantum technologies due to their long coherence times and excellent control fidelities.
Qubits and qudits have been encoded on donor
nuclei, with successful demonstrations of Bell states and
quantum memories on the
spin-1/2 $^{31}$P and cat-
qubits on the
spin-7/2 $^{123}$Sb
nuclei. Isoelectronic
nuclear spins coupled to gate-defined
quantum dots, such as the naturally occurring $^{29}$Si isotope, possess no additional charge and allow for the coupled electron to be shuttled without destroying the
nuclear spin coherence. Here, we demonstrate the coupling and readout of a
spin-9/2 $^{73}$Ge
nuclear spin to a gate-defined
quantum dot in SiMOS. The $^{73}$Ge
nucleus was implanted by isotope-selective ion-implantation. We observe the hyperfine interaction (HFI) to the coupled
quantum dot electron and are able to tune it from 180 kHz to 350 kHz, through the voltages applied to the lateral gate electrodes. This work lays the foundation for future
spin control experiments on the
spin-9/2 qudit as well as more advanced experiments such as
entanglement distribution between distant
nuclear spins or repeated weak measurements.
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All authors Paul Steinacker, Gauri Goenka, Rocky Yue Su, Tuomo Tanttu, Wee Han Lim, Santiago Serrano, Tim Botzem, Jesus D. Cifuentes, Shao Qi Lim, Jeffrey C. McCallum, Brett C. Johnson, Fay E. Hudson, Kok Wai Chan, Christopher C. Escott, Andre Saraiva, Chih Hwan Yang, Vincent Mourik, Andrea Morello, Andrew S. Dzurak, Arne Laucht