Disordered Systems and Neural Networks
Empirical universality and non-universality of local dynamics in the Sherrington-Kirkpatrick model
Grace Liu and Dmitriy Kunisky
Several recent works have aimed to design
algorithms for optimizing the
Hamiltonians of
spin glass models from statistical physics. While Montanari (2018) eventually gave a sophisticated message-passing
algorithm to do this nearly optimally for the Sherrington-Kirkpatrick (SK) model, the recent work of Erba, Behrens, Krzakala, and Zdeborová (2024) also observed that a simple yet unusual
algorithm first proposed by Parisi (2003) seems to perform just as well: perform local reluctant search, repeatedly making the local adjustment improving the objective function by the smallest possible amount. This is in contrast to the more intuitive local greedy search that repeatedly makes the local adjustment improving the objective by the largest possible amount. We study empirically how the performance of these
algorithms depends on the distribution of entries of the coupling
matrix in the SK model. We find evidence that, while the runtime of greedy search enjoys universality over a broad range of distributions, the runtime of reluctant search surprisingly is not universal, sometimes depending quite sensitively on the entry distribution. We propose that one mechanism leading to this non-universality is a change in the behavior of reluctant search when the couplings have discrete support on an evenly-spaced grid, and give experimental results supporting this proposal and investigating other properties of a distribution that might affect the performance of reluctant search.
Read the full abstract ▾
Superconductivity
Flat band surface state superconductivity in thick rhombohedral graphene
Yi Guo, Owen I. Sheekey, Trevor Arp et al. (+11 more)
Rhombohedral multilayer
graphene has recently emerged as a rich platform for studying correlation driven
magnetic, topological and superconducting states. While most experimental efforts have focused on devices with N$\leq 9$ layers, the electronic structure of thick rhombohedral
graphene features flat-band surface states even in the infinite layer limit. Here, we use layer resolved capacitance measurements to directly detect these surface states for $N\approx 13$ layer rhombohedral
graphene devices. Using electronic transport and local magnetometry, we find that the surface states host a variety of
ferromagnetic phases, including both valley imbalanced quarter metals and broad regimes of density in which the system spontaneously
spin polarizes. We observe several superconducting states localized to a single surface state. These
superconductors appear on the unpolarized side of the density-tuned
spin transitions, and show strong violations of the Pauli limit consistent with a dominant attractive interaction in the
spin-triplet, valley-singlet pairing channel. In contrast to previous studies of rhombohedral multilayers, however, we find that superconductivity can persist to zero displacement field where the system is inversion symmetric. Energetic considerations suggest that superconductivity in this regime is described by the existence of two independent surface
superconductors coupled via tunneling through the insulating single
crystal graphite bulk.
Read the full abstract ▾
All authors Yi Guo, Owen I. Sheekey, Trevor Arp, Kryštof Kolář, Thibault Charpentier, Ludwig Holleis, Ben Foutty, Aidan Keough, Maya Kang-Chou, Martin E. Huber, Takashi Taniguchi, Kenji Watanabe, Cyprian Lewandowski, Andrea F. Young
Strongly Correlated Electrons
Measuring Anyonic Exchange Phases Using Two-Dimensional Coherent Spectroscopy
Nico Kirchner, Wonjune Choi and Frank Pollmann
Identifying experimental signatures of anyons, which exhibit fractional exchange statistics, remains a central challenge in the study of two-dimensional topologically ordered systems. Previous theoretical work has shown that the threshold behavior in linear response spectroscopy can reveal the fractional exchange statistics between an anyon and its antiparticle. In this work, we extend this framework to nonlinear, two-dimensional coherent spectroscopy. We demonstrate by analyzing time-ordered four-point correlation functions that the threshold behavior of nonlinear response functions encodes the fractional statistics between general pairs of anyons that can combine to any composite topological charge. This feature in particular provides a powerful probe for unambiguously distinguishing non-Abelian anyons, which can form multiple composite charges with distinct nontrivial braid statistics. Our approach is validated using numerical simulations that are consistent with the correct fractional exchange statistics for both the Abelian anyons in the toric code and non-Abelian Ising anyons.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Breakdown of chiral anomaly and emergent phases in Weyl semimetals under orbital magnetic fields
Faruk Abdulla, Anna Keselman and Daniel Podolsky
An external orbital
magnetic field applied perpendicular to the separation vector of a pair of Weyl points can couple them and induce a gap in the electronic spectrum. In this work, we investigate the gap-opening behavior in the presence of a
lattice, revealing rich phenomenology absent in the continuum picture. Specifically, we address the emergence of layered Chern insulating states, examining how the anisotropy of the Weyl cone dispersion influences the sequence of phase transitions, and establishing connections to the continuum limit. We analyze the
evolution of surface
Fermi-arc states across these regimes, highlighting their distinct behaviors during the gap-opening transitions.
Read the full abstract ▾
Materials Science
Momentum-Resolved Electronic Structure and Orbital Hybridization in the Layered Antiferromagnet CrPS$_4$
Lasse Sternemann, David Maximilian Janas, Eshan Banerjee et al. (+8 more)
Chromium thiophosphate (CrPS$_4$) is a layered two-dimensional
antiferromagnetic semiconductor exhibiting intriguing spintronic and magneto-optical properties, yet its electronic band structure has remained experimentally uncharacterized. Here, we employ momentum-resolved photoemission spectroscopy above and below the Néel temperature, complemented by density functional theory with Hubbard U corrections (DFT+U), to reveal a valence band dominated by Cr $3d$ and S $3p$ states with a ligand-to-metal charge-transfer band gap. We identify weakly hybridized t$_{2g}$ orbitals responsible for
magnetic ordering and strongly hybridized e$_{g}$ orbitals that relax dipole selection rules, enabling optically active orbital transitions. These findings establish a foundational understanding of CrPS$_4$'s electronic structure, providing a
benchmark for theoretical models and informing future investigations into its orbital physics and potential device applications.
Read the full abstract ▾
All authors Lasse Sternemann, David Maximilian Janas, Eshan Banerjee, Richard Leven, Jonah Elias Nitschke, Marco Marino, Leon Becker, Ahmet Can Ademoğlu, Frithjof Anders, Stefan Tappertzhofen, Mirko Cinchetti
Materials Science
Crystal Growth and Physical Properties of Orthorhombic Kagome Lattice Magnets $R$Fe$_6$Ge$_6$ ($R$=Y, Tb, Dy)
Abhijeet Nayak, Sk Jamaluddin, Fan Wu et al. (+10 more)
Kagome magnets represent a promising class of materials that exhibit intriguing electronic and
magnetic properties, and they have recently garnered significant
attention. While most kagome-
lattice compounds are hexagonal, we report here single-
crystal growth and physical property measurements of $R$Fe$_6$Ge$_6$ ($R$ = Y, Dy, Tb) compounds, which crystallize in an orthorhombic structure. The structure can be derived from a hexagonal prototype $R$Fe$_3$Ge$_2$ by replacing every other $R$ atom with a covalent Ge$_2$ dimer. Ordering of these dimers renders the structure orthorhombic, slightly distorts the kagome net, and makes the three Fe sites formally inequivalent. The iron and rare-earth sublattices order independently. Fe moments order above 400 K, forming
ferromagnetic kagome planes stacked antiferromagnetically, while rare-earth moments order below 9 K. TbFe$_6$Ge$_6$ exhibits a single
magnetic ordering transition associated with the Tb atoms, whereas DyFe$_6$Ge$_6$ shows two distinct
magnetic phase transitions, strongly influenced by
crystal electric field effects on the Dy$^{3+}$ ions. Density functional theory (DFT) calculations indicate that the
ferromagnetic ordering of the Fe planes is driven by a high density of states at the
Fermi energy. They also reveal three dramatically different structural energy scales: $R$ and Ge$_2$ form alternating 1D chains perpendicular to the kagome planes, and violating this alternation incurs a large energy cost. Aligning these chains is less costly, and achieving a two-dimensional order of anti-aligned chains requires very little energy. These compounds represent a unique class of materials, offering new opportunities to investigate the interplay between the distinct
crystal lattice geometry and the underlying electronic and
magnetic properties.
Read the full abstract ▾
All authors Abhijeet Nayak, Sk Jamaluddin, Fan Wu, Emily Rapp, Resham Babu Regmi, Mohamed El Gazzah, Bence G. Márkus, László Forró, Madhav P. Ghimire, Allen Oliver, Kateryna Foyevtsova, Igor I. Mazin, Nirmal J. Ghimire
Disordered Systems and Neural Networks
Non-Hermitian impurity problem
E. T. Kokkinakis, I. Komis, K. G. Makris et al. (+1 more)
The problem of a single Hermitian
impurity has long served as a cornerstone in condensed matter physics, offering fundamental insights into the mechanisms of Anderson localization. Yet, despite the increased interest in the spectral and localization properties of non-Hermitian
lattices with defects, the non-Hermitian extension of the single
impurity problem remains largely unexplored. In this work, we investigate the role of a single complex
impurity in one-, two-, and three-dimensional infinite tight-binding
lattices. Our study reveals a series of counterintuitive phenomena, including regions where localization vanishes and re-emerges as the
impurity strength varies. Next, we study the corresponding finite-sized
lattices, which are highly relevant to experimental realizations in readily accessible photonic platforms, revealing a variety of exotic features, such as scale-free localized states, exceptional points, and peculiar cross-shaped localized eigenstates, whose profiles deviate from the conventional exponential localization. This work paves the way for future studies on transport phenomena in non-Hermitian disordered
lattices.
Read the full abstract ▾
All authors E. T. Kokkinakis, I. Komis, K. G. Makris, E. N. Economou
Mesoscale and Nanoscale Physics
Building 3D superconductor-based Josephson junctions using a via transfer approach
Cequn Li, Le Yi, Kalana D. Halanayake et al. (+8 more)
The coupling of superconductivity to unconventional materials may lead to novel
quantum states and potential applications. Controlling the quality of the
superconductor-normal metal interface is of crucial importance to the understanding and engineering of the superconducting proximity effect. In many cases, conventional lithography-based deposition methods introduce undesirable effects. Using the concept of via contact and dry transfer, we have constructed smooth, van der Waals-like contact between 3D superconducting NbN/Pd and
graphene with low contact resistance of approximately 130 $\Omega \cdot \mu m$. Gate-tunable supercurrent, Fraunhofer pattern, and Andreev reflections are observed, the properties of which can be understood using an induced superconducting gap $\Delta$' in this planar contact geometry. We discuss potential mechanisms impacting the magnitude of $\Delta$' and suggest ways of further increasing the proximity coupling. This gentle, lithography-free contacting method can be applied to air- and damage-sensitive surfaces to engineer novel superconducting
heterostructures.
Read the full abstract ▾
All authors Cequn Li, Le Yi, Kalana D. Halanayake, Jessica L. Thompson, Yingdong Guan, Kenji Watanabe, Takashi Taniguchi, Zhiqiang Mao, Danielle Reifsnyder Hickey, Morteza Kayyalha, Jun Zhu
Strongly Correlated Electrons
Critical Berezinskii-Kosterlitz-Thouless dynamics in the archetypal two-dimensional spin system Ba$_2$CuSi$_2$O$_6$Cl$_2$
K. M. Ranjith, Maxime Dupont, Steffen Krämer et al. (+6 more)
We study the
spin dynamics in the quasi-2D
spin-$1/2$ dimer compound Ba$_2$CuSi$_2$O$_6$Cl$_2$, which exhibits a
magnetic field-induced Bose-Einstein condensate (BEC) of triplons. Using
nuclear magnetic resonance
spin-
lattice relaxation rate ($T_1^{-1}$) measurements combined with large-scale
quantum Monte Carlo (QMC) simulations, we investigate critical fluctuations across the field-temperature phase diagram. Bridging the behavior observed in 1D and 3D systems, the $T_1^{-1}$ relaxation rate shows a pronounced peak extending well above the Néel temperature $T_N$, indicating strong two-dimensional Berezinskii-Kosterlitz-Thouless (BKT)-type fluctuations. A quantitative match between experimental and theoretical BEC phase boundaries validates an effective XXZ model. The study determines the intrinsic BKT transition temperature $T_{\mathrm{BKT}}$ from QMC, revealing a nearly field-independent $T_{\mathrm{BKT}}/T_N \approx 0.74$. Scaling analysis of the relaxation rate shows critical exponents consistent with 2D universality, and a narrow temperature window is identified where 2D physics dominates. These findings establish Ba$_2$CuSi$_2$O$_6$Cl$_2$ as a model system for exploring BKT dynamics in
quantum magnets.
Read the full abstract ▾
All authors K. M. Ranjith, Maxime Dupont, Steffen Krämer, Sylvain Capponi, Edmond Orignac, Nicolas Laflorencie, Nobuyuki Kurita, Hidekazu Tanaka, Mladen Horvatić
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Robust detection of an entanglement transition in the projective transverse field Ising model
Felix Roser, Etienne M. Springer, Hans Peter Büchler et al. (+1 more)
We propose a scalable and noise-resilient protocol for the detection of the
entanglement transition in a projective version of the transverse field Ising model.
Entanglement transitions are experimentally difficult to observe due to the inherent randomness of projective measurements and noise in large-scale experimental settings. Our approach combines error correction
algorithms with classical shadow
tomography to overcome both problems. This allows for experimentally accessible upper and lower bounds on the
entanglement transition without postselection or full state
tomography. These bounds remain robust under noise and their sharpness is a measure of the noise rate.
Read the full abstract ▾
All authors Felix Roser, Etienne M. Springer, Hans Peter Büchler, Nicolai Lang
Soft Condensed Matter
DoS Dos and Don'ts
Lucas Warwaruk, Konstantinos Zinelis, Randy H. Ewoldt et al. (+2 more)
Dripping-onto-Substrate (DoS) rheometry is a well-established method for measuring the extensional rheology of low-viscosity
liquids. However, clear guidelines on the capabilities and limitations of the technique are lacking. In the present work, we define operational limits for measuring a transient extensional viscosity directly from observation of the rate of filament thinning, as well as model-based bounds on calculating a viscosity $\eta$ and extensional relaxation time $\tau_E$ of a
liquid using DoS. Dilute solutions of polyethylene
oxide (PEO) and polyacrylamide (PAM) are used to probe the lower limit of measurable $\tau_E$, demonstrating that values as low as 0.1 ms can be resolved, provided (a) the intrinsic Deborah number (based on the ratio of the relaxation time and the Rayleigh breakup time scale) is $De \geq \mathcal{O}(0.1)$ and (b) an instrumental constraint related to spatial and temporal resolution is satisfied. This instrumental constraint is quantified through a new metric we define as the filament capture rate, a “figure of merit” (expressed in Hz) that can be used to quantify the number of data points within the elasto-capillary regime that are available for extraction of $\tau_E$. We also investigate the sensitivity to other experimental parameters including variations in nozzle radius and Bond number ($Bo$). Across the tested range ($0.2 < Bo < 0.7$), extensional relaxation times for the same fluid vary by less than $\pm16$ %; however, experiments with low viscosity fluids at $Bo > 0.5$ exhibit damped gravitational oscillations that affect early-time dynamics. Collectively, these results provide a quantitative roadmap for reliable DoS rheometry and affirm its use for measuring sub-millisecond relaxation times in weakly elastic fluids.
Read the full abstract ▾
All authors Lucas Warwaruk, Konstantinos Zinelis, Randy H. Ewoldt, Christopher W. Macosko, Gareth H. McKinley
Quantum Gases · Cross-listed from physics.optics
Aspects of quantum geometry in photonic time crystals
Karthik Subramaniam Eswaran, Ali Emami Kopaei and Krzysztof Sacha
We develop a
geometric description of
quantum light in photonic time
crystals on the SU(1,1) coherent-state
manifold. In a projective picture, the
evolution of each mode appears as a Möbius isometry on the Poincaré disk, where
topologies of trajectories distinguish stable, unstable, and critical regimes. The
geometric phase is related to the
hyperbolic area enclosed by cyclic paths in the complex projective
Hilbert space. This framework offers an intuitive view of stability and
topology in
quantum photonic time
crystals.
Read the full abstract ▾
Statistical Mechanics
Unveiling the degeneracy of bound magnon crystals from magnetic and thermodynamic features of the spin-1/2 Heisenberg octahedral chain
Jozef Strecka and Michal Nemcik
Magnetic, thermodynamic, and magnetocaloric properties of a
spin-1/2 Heisenberg octahedral chain with three distinct exchange interactions are investigated in an external
magnetic field using the variational method, extended localized-
magnon approach, and exact diagonalization. Variational arguments rigorously establish two distinct fragmented phases in the frustrated regime. In the former phase all four
spins of each square plaquette form a collective plaquette singlet, whereas in the latter phase two dimer singlets are formed along diagonals of each square plaquette. These bound two-
magnon states, supplemented with three localized one-
magnon states, enable us to elaborate a generalized localized-
magnon theory that is applicable in a frustrated regime across the entire field range as confirmed by comparison with exact diagonalization data. The concept of localized
magnons provides a consistent description of low-temperature magnetization curves featuring intermediate one-fifth and three-fifths plateaus, which intersect each other at temperature-independent crossing points determined by the relative degeneracies of competing bound-
magnon phases. Field variations of the specific heat reveal a pronounced double-peak structure near each field-driven transition with peak heights depending on the relative degeneracies of the respective bound-
magnon states. Our results demonstrate that the system supports highly efficient cooling via adiabatic demagnetization, making it a promising candidate for magnetocaloric refrigeration.
Read the full abstract ▾
Soft Condensed Matter
Polyampholyte model of ion clusters: double-layer interactions in the presence of dissociated simple salt
David Ribar, Clifford E Woodward and Jan Forsman
We explore interactions between equally charged surfaces, in the presence of simple salt and either neutral or monovalently charged polyampholytes. We consider the possibility of using these charged
polymers as crude models of ion clusters. The latter have been hypothesised to form in concentrated aqueous salt solutions, and are possibly related to anomalous underscreening. This phenomenon usually manifests itself by unexpectedly strong and long-ranged effective forces at very high ionic strengths. If ion clusters are formed, they are expected to carry at most a weak net charge. Keeping this in mind, we investigate how polyampholyte chains mediate interactions between charged surfaces. A significant amount of simple salt is also present, in most cases. We highlight that if the charges of the polyampholytes are unevenly distributed, there is a polarisation response that in turn can generate very strong and long-ranged surface forces, even at rather high concentrations of simple salt. Aside from their possible relevance to ion clusters and underscreening phenomena, these results also suggest the possibility of tailoring synthetic polyampholytes, in order to regulate colloidal stability.
Read the full abstract ▾
Materials Science
Altermagnetic Flatband-Driven Fermi Surface Geometry for Giant Tunneling Magnetoresistance
Xingyue Yang, Shibo Fang, Zongmeng Yang et al. (+3 more)
Altermagnetism, characterized by zero net magnetization and
symmetry-protected
spin-split band structures, has recently emerged as a promising platform for spintronics. In altermagnetic tunnel junctions (AMTJs), the suppression of tunneling in the antiparallel configuration relies on the mismatch between
spin-polarized conduction channels in momentum space. However, ideal nonoverlapping
spin-polarized
Fermi surfaces are rarely found in bulk altermagnets. Motivated by the critical influence of
Fermi surface geometry on tunneling magnetoresistance (TMR), we investigate three experimentally synthesized altermagnets – bulk $\mathrm{V_2Te_2O}$, $\mathrm{RbV_2Te_2O}$, and $\mathrm{KV_2Se_2O}$ – to elucidate how flatband-driven
Fermi surfaces minimize
spin-channel overlap and boost AMTJ performance. Notably, $\mathrm{RbV_2Te_2O}$ and $\mathrm{KV_2Se_2O}$ host flat altermagnetic
Fermi sheets, which confine
spin degeneracy to minimal arc-like or nodal-like regions. Such
Fermi surface geometry drastically reduces
spin overlap, resulting in an unprecedented intrinsic TMR well over $10^3\%$ in the $\mathrm{KV_2Se_2O}$-based AMTJ. Incorporating an insulating barrier further enhances the TMR to $\sim10^6\%$, surpassing most conventional MTJs. These results not only establish $\mathrm{KV_2Se_2O}$ as a compelling candidate AMTJ material, but also highlight the critical role of flatband
Fermi surface geometry in achieving high-performance altermagnetic-spintronic device technology.
Read the full abstract ▾
All authors Xingyue Yang, Shibo Fang, Zongmeng Yang, Pin Ho, Jing Lu, Yee Sin Ang
Soft Condensed Matter
Numerical study of the effect of the relative mobilities of chemical components on the Non solvent induced phase separation process for membrane elaboration
Abderraouf Bounjad, Aoran Wu, Cyril Chevarin et al. (+6 more)
The filtration membranes are often elaborated through a phase separation process where a
polymer rich phase and a
polymer poor phase spontaneously form through spinodal decomposition. One process that is still not well understood from a theoretical point of view is the Non-Solvent induced phase separation where a thermodynamically stable film of a a
polymer mixture is put in contact with a bad solvent of the
polymer. The invasion of the film by this non-solvent drives the film out of stability and leads to spinodal decomposition. During this phase separation
polymer poor and
polymer rich regions form. In this article we present a numerical study of the effect of kinetic coefficients: namely the relative mobilities of
polymer and solvent/non-solvent on the observed patterns. Using 2D numerical simulations of the ternary Cahn-Hilliard model we show that for a given thermodynamic landscape, this parameter has dramatic effects: depending on its value phase separation can be observed or not. We also show that it can affect the nature of the observed pattern. In addition analysing 3D simulations we analyse the final pattern using a quantitative indicator of its connectivity and show that for a wide range of initial composition of the film the final pattern is bicontinuous. We also quantify the transport properties of both
polymer rich and
polymer poor domains.
Read the full abstract ▾
All authors Abderraouf Bounjad, Aoran Wu, Cyril Chevarin, Patrick Guenoun, Florent Mallogi, Jean-Pierre Mericq, Charaff Merzougui, Denis Bouyer, Hervé Henry
Soft Condensed Matter
Molecular insight on ultra-confined ionic transport in wetting films: the key role of friction
Aymeric Allemand, Anne-Laure Biance, Christophe Ybert et al. (+1 more)
Nanofluidic transport is ubiquitous in natural systems from extra-cellular communication in biology to geological phenomena, and promotes the emergence of new technologies such as energy harvesting and water desalination. While experimental access to ultraconfined fluids has advanced rapidly, their behavior challenges conventional theoretical descriptions based on Poisson-Boltzmann theory or the Stokes equation whose possible extension remains an open question. In this work, we use molecular dynamics simulations to investigate ionic transport within wetting films of water confined on silica surfaces down to the sub-nanometer scale. We then analyze these results using a simple one-dimensional theoretical framework. Remarkably, we show that this model remains valid even at confinement close to the molecular scale. Our results reveal that the dynamic of ion plays a key role in ionic transport, through ion adsorption at the water-silica interface. Adsorbed cations do not participate in ionic conduction, but instead generate molecular-scale roughness and transmit additional frictional forces to the substrate. This mechanism produces an apparent viscosity increase in electrostatically driven flows, reaching up to four times the bulk value in the case of potassium. Our findings highlight the critical role of interfacial ion adsorption in nanoscale hydrodynamics and provide new insights for interpreting experiments and designing nanofluidic systems.
Read the full abstract ▾
All authors Aymeric Allemand, Anne-Laure Biance, Christophe Ybert, Laurent Joly
Superconductivity · Cross-listed from quant-ph
Basic cell for a quantum microwave router
Evgeniya Mutsenik, Aidar Sultanov, Leonie Kaczmarek et al. (+4 more)
We report the first experimental realization of a scalable basic
cell for
quantum routing, enabling coherent control and exchange of microwave
photons between two spatially separated superconducting waveguides coupled via a single transmon
qubit. The
cell was characterized at 10 mK with an average input signal of approximately 1
photon at approximately 6 GHz, and with the
qubit biased to its optimal point to minimize sensitivity to external
magnetic fluctuations. By combining steady-state and time-domain measurements, we reconstructed the key parameters of the system, including
qubit relaxation and dephasing, waveguide-
qubit couplings, and cross-waveguide
photon transfer efficiency. The observed performance is consistent with a non-Hermitian
Hamiltonian formalism and demonstrates clear limits set by flux bias, temperature, and
photon number, in agreement with flux- and temperature-induced dephasing models. Crucially, the
cell operates reliably at the single-
photon level, and in the high-
photon regime we directly observe
photon dressing induced by the
qubit. These results establish a versatile platform for studying open
quantum system phenomena and pave the way for scalable implementations of
quantum routing and network nodes.
Read the full abstract ▾
All authors Evgeniya Mutsenik, Aidar Sultanov, Leonie Kaczmarek, Matthias Schmelz, Gregor Oelsner, Ronny Stolz, Evgeni Ilichev
Statistical Mechanics
Simulated Annealing for Quadratic and Higher-Order Unconstrained Integer Optimization
Kohei Suzuki
Simulated annealing (SA) is a key
algorithm for solving combinatorial optimization problems, which model numerous real-world systems. While SA is commonly used to solve quadratic unconstrained binary optimization (QUBO) problems, many practical problems are more naturally formulated using integer variables. We therefore study quadratic and higher-order unconstrained integer optimization (QUIO and HUIO) problems, which generalize QUBO by allowing integer-valued variables and higher-order interactions. Conventional approaches often convert these problems into QUBO formulations through binary encoding and the reduction of higher-order terms. Such conversions, however, greatly increase the number of variables and interactions, resulting in long computation times and, for large-scale problems, even making the conversion itself a dominant computational bottleneck. To overcome this limitation, we propose an efficient framework that directly applies SA to QUIO and HUIO problems without converting them into QUBO. Within this framework, we introduce an optimal-transition Metropolis method, designed to improve efficiency when the variable range is wide, and evaluate its performance alongside the conventional Metropolis and heat bath methods. Numerical experiments demonstrate that the proposed direct approach achieves higher efficiency and better solution quality than the conventional QUBO-based formulation and reveal the practical advantages of the optimal-transition Metropolis method. The
algorithm developed in this study is available as part of the open-source library OpenJij, which provides a Python front end with a C++ backend.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Coexistence of unconventional spin-orbit torque and in-plane Hall effect in a single ferromagnetic layer
Jiaxin Chen, Hongsheng Zheng, Hongliang Chen et al. (+18 more)
The
symmetry of a material fundamentally governs its
spin transport properties. While unconventional
spin transport phenomena have been predominantly explored in low-
symmetry systems (e.g., $C_{1v}$
symmetry), high-
symmetry crystals–which constitute the majority of industry-compatible materials–are generally expected to exhibit only conventional
spin-transport behavior. Here, we report the coexistence of two unconventional
spin transport effects, the
crystal spin-orbit torque (CSOT) and the
crystal in-plane
Hall effect (CIHE), in a CoPt single
ferromagnetic layer with $C_{3v}$
symmetry. Leveraging the CSOT, we achieve nearly 100% field-free perpendicular magnetization switching in a 6 nm CoPt layer at room temperature. Simultaneously, the CIHE observed in this material exhibits nearly identical dependencies on both current angle and growth temperature as the CSOT.
Symmetry analysis confirms that both effects share a common physical origin. Our work not only establishes CoPt as a high-performance
spin-orbit material, but also demonstrates that unconventional
spin transport can be realized in high-
symmetry systems, thereby opening a broad pathway for their application in practical spintronics.
Read the full abstract ▾
All authors Jiaxin Chen, Hongsheng Zheng, Hongliang Chen, Qia Shen, Chang Pan, Zhenyi Zheng, Hemian Yi, Dandan Guan, Xiaoxue Liu, Yaoyi Li, Shiyong Wang, Hao Zheng, Canhua Liu, Jinfeng Jia, Jingsheng Chen, Ruidan Zhong, Lei Wang, Xuepeng Qiu, Yumeng Yang, Aurélien Manchon, Liang Liu
Materials Science · Cross-listed from physics.acc-ph
A Short Introduction to Metal Forming
Charbel Moussa and Pierre Montmitonnet
The present paper is a short introduction to metal forming. The paper highlights the different disciplines that should be considered when analyzing metal forming. Hence, mechanical flow, heat flow, mechanical and thermal contact, and microstructure
evolution are presented within the perspective of metal forming. For every aspect, well-established knowledge is presented in addition to scientific open questions on which active research is still done.
Read the full abstract ▾
Materials Science · Cross-listed from physics.app-ph
Ferroelectric Nematic Liquid Crystals as Charge Boosters for Triboelectric Nanogenerators
Jia-Yao Ye, Susanta Chakraborty, Karthick Subramani et al. (+3 more)
Driven by growing demand for clean energy, triboelectric nanogenerators (TENGs) have emerged as promising self-powered systems, yet achieving high charge density remains a critical challenge. In
polymer dielectrics, triboelectricity can be further amplified by incorporating high-dielectric and polar materials for functional adaptability. Conventional dielectrics, including
liquid crystals (LCs), offer limited improvement for triboelectrification, whereas the breakthrough ferroelectric nematic
liquid crystals (NF-LCs), with
giant spontaneous polarization and high dielectric constant, act as highly effective charge boosters. Here, we introduce NF-LC (DIO) as a functional filler in a PVDF-based TENG. Increasing DIO content progressively grows the electroactive phase and effective polarization in PVDF and defines a marked improvement in TENGs electrical performances through favourable dipolar
alignment and strengthened charge-trap effects. The optimized composite film achieves an impressive open-
circuit voltage of 1.1 kV, short-
circuit current of 50 micro Amp, and power density of 110 W/m2 - seven times higher than pure PVDF. The device exhibits excellent charge-storage capability, powers over 500 LEDs without power management. This work establishes NF-LC-based TENGs as a new platform for high-performance self-powered energy harvesting, linking soft matter physics with applied energy technology.
Read the full abstract ▾
All authors Jia-Yao Ye, Susanta Chakraborty, Karthick Subramani, Xing-Zhou Tang, Yan-Nan Xie, Bing-Xiang Li
Materials Science
Ferroelectric Switchable Topological Magnon Hall Effect in Type-I Multiferroics
Quanchao Du, Jinlian Lu, Xueqing Wan et al. (+2 more)
Electric control of magnetism at room temperature is crucial for developing next-generation, low-power spintronic devices. However, the intrinsic incompatibility between ferroelectricity and magnetism in
crystal symmetry, along with the absence of strong magnetoelectric coupling mechanisms, continues to pose major challenges. In this work, we propose a general theoretical framework for
magnon manipulation based on ferroelectric polarization switching in two-dimensional multiferroics. Taking monolayer multiferroics $\mbox{Ti}_{2}\mbox{F}_{3}$ as an example, our calculations demonstrate that ferroelectric switching can significantly modulate
spin exchanges, thereby enabling nonvolatile and reversible electric control of the
magnons. More importantly, the ferroelectric polarization reversal leads to a sign change in the Berry
curvature, ensuring effective control over the valley
Hall and nonlinear
Hall response of
magnons. This study provides a new way for realizing low-power and electrically controllable magnonic devices.
Read the full abstract ▾
All authors Quanchao Du, Jinlian Lu, Xueqing Wan, Zhenlong Zhang, Zhijun Jiang
Mesoscale and Nanoscale Physics
Josep Ingla-Aynés, Serhii Volosheniuk, Talieh S. Ghiasi et al. (+5 more)
The interaction between itinerant electrons and localized
spins is key to a wide range of electronic phenomena. Of particular interest is the regime where the interacting electrons exhibit both
spin and valley degeneracy, resulting in SU(4) Kondo physics. However, this regime is challenging to realize in typical mesoscopic systems because it requires a strong interaction between electrons, resulting in a Kondo temperature ($T_\mathrm{K}$) significantly larger than the
spin and valley splittings. Here, we present conductance measurements of a
quantum point contact (QPC) in
bilayer graphene (BLG). Beyond the expected quantized conductance plateaus, which reflect
spin and valley degeneracy, we observe an additional subband, known as `0.7 anomaly' exhibiting signatures of Kondo physics and a $T_\mathrm{K}$ ranging from approximately 0.5 up to 2.4 K at zero
magnetic field, corresponding to Kondo energies between 40 and 200 $\mu$eV. Given that the
spin-orbit splitting in BLG is between 40 and 80 $\mu$eV, we argue that these results are consistent with a transition between four-fold degenerate SU(4) and two-fold degenerate
spin-valley locked SU(2) Kondo effects. Furthermore, we break the valley degeneracy of the lowest subband by an out-of-plane
magnetic field and show that Kondo signatures remain present, indicating a transition from SU(4) to a valley-polarized SU(2) Kondo effect, and showing the versatility of BLG QPCs for exploring many-body effects.
Read the full abstract ▾
All authors Josep Ingla-Aynés, Serhii Volosheniuk, Talieh S. Ghiasi, Angelika Knothe, Kenji Watanabe, Takashi Taniguchi, Vladimir I. Fal'ko, Herre S. J. van der Zant
Strongly Correlated Electrons
Probing Boundary Spins in the Su-Schrieffer-Heeger-Hubbard model
Armando A. Aligia, Alejandro M. Lobos, Lucila Peralta Gavensky et al. (+1 more)
Studying boundary excitations provides a powerful approach to probe correlations in topological phases. We propose that localized
spins near the ends of a Su-Schrieffer-Heeger-Hubbard chain embedded in an insulating environment can be detected experimentally using scanning tunneling microscopy (STM) combined with electron
spin resonance (ESR). When the STM tip is in the contact regime, the tip-end-
spin coupling realizes an effective Anderson
impurity problem, giving rise to a Kondo peak at low bias. Spatially resolving the Kondo resonance width as the STM tip approaches the chain ends provides an indirect yet clear signature of these localized
spins. To support this proposal, we use density-
matrix renormalization group (DMRG) to calculate the
spin gap and
spin projection of end states for chains of various lengths and interaction strengths $U$ at half-filling. In the non-interacting limit ($U=0$), we derive simple analytical expressions that reproduce the numerical results for sufficiently long chains. We also discuss how the correlated phase of the isolated chain is characterized by boundary zeros in its single-particle Green's function, and briefly comment on their localization properties in relation to the boundary
spins.
Read the full abstract ▾
All authors Armando A. Aligia, Alejandro M. Lobos, Lucila Peralta Gavensky, Claudio J. Gazza
Statistical Mechanics · Cross-listed from quant-ph
The Scrooge ensemble in many-body quantum systems
Max McGinley and Thomas Schuster
In many physical settings, the statistical properties of
quantum states are thought to be described by the Scrooge ensemble, a more structured generalization of the Haar ensemble. In this work, we prove several key results on the properties and complexity of Scrooge-random states in macroscopic
quantum systems, and provide a general-purpose calculus for evaluating their moments. A key theme of our results is a separation between universal random fluctuations in non-local properties and exponential concentration of all local properties. Implications for device benchmarking, sampling advantages beyond random
circuits,
quantum complexity growth, and the physical origin of Scrooge-random states are discussed.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Enhanced Efficiency of Intermediate-Band Semiconductor Solar Cells Embedded with Quantum Dot Superlattices
Naira Petrosyan, Lilit Yeganyan, Aram Manaselyan et al. (+3 more)
We present a multiscale approach for modeling an intermediate-band
solar cell based on a GaAs-GaAlAs
quantum dot superlattice of cubic
symmetry. Our framework combines high-accuracy theoretical calculations of the superlattice band structure and miniband-related absorption coefficient with experimentally determined interband absorption data. The
quantum-mechanically derived absorption spectrum is incorporated into a drift-
diffusion transport model in COMSOL Multiphysics, where key processes, including thermal and radiative recombination, are taken into account. This integrated methodology enables realistic modeling of device performance. Our results identify an optimal superlattice constant of 14 nm, yielding a maximum
solar cell efficiency of 13.3 percent. Further increase in the superlattice constant enhances the miniband-related absorption peak but reduces the generation rate in the n-type region, resulting in a net efficiency decrease. The proposed approach, integrating theoretical, experimental, and computational components, provides a reliable framework for assessing
solar cells based on
quantum dot superlattices.
Read the full abstract ▾
All authors Naira Petrosyan, Lilit Yeganyan, Aram Manaselyan, Vram Mughnetsyan, Vidar Gudmundsson, Albert Kirakosyan
Strongly Correlated Electrons
Anyon Quasilocalization in a Quasicrystalline Toric Code
Soumya Sur, Mohammad Saad and Adhip Agarwala
An exactly solvable model of a
quantum spin liquid on a quasicrystal, akin to Kitaev's honeycomb model, was introduced in Kim et al., \href{https://doi.org/10.1103/PhysRevB.110.214438}{\text{Phys. Rev. B} 110, 214438 (2024)}. It was shown that in contrast to the translationally invariant models, such a
spin liquid stabilizes a gapped ground state with a finite irrational flux density. In this work, we analyze the strong bond-anisotropic limit of the model and demonstrate that the aperiodic
lattice geometry naturally generates a hierarchy of exponentially separated coupling constants in the resulting toric code
Hamiltonian. Furthermore, a perturbative
magnetic field leads to anomalous localization properties where an anyonic excitation sequentially delocalizes over subsets of sites forming equipotential contours in the quasicrystal. In addition, certain background flux configurations, together with the underlying geometry, give rise to strictly localized eigenstates that remain decoupled from the rest of the spectrum. Using numerical studies, we uncover the key mechanisms responsible for this unconventional localization behavior. Our study highlights that topologically ordered phases, in the presence of geometrical constraints can lead to highly anomalous localization properties of fractionalized charges.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Single-Defect Spectroscopy via Random Telegraph Noise in Graphene-Contacted ReS$_2$-hBN Heterostructures
Shubhrasish Mukherjee, Gaurab Samanta, Shubhadip Moulick et al. (+5 more)
Defect spectroscopy in two-dimensional (2D) field-effect transistors (FETs) requires device architectures that suppress contact and disorder artifacts while preserving intrinsic carrier dynamics. Here, we demonstrate ReS$_2$-hBN FETs with few-layer
graphene (FLG) van der Waals contacts that form nearly barrier-free interfaces, enabling intrinsic transport in ReS$_2$, an anisotropic, low-
symmetry TMDC rarely exhibiting disorder-free behavior. The clean ReS$_2$-FLG platform allows direct observation of random telegraph noise (RTN) even in micron-scale channels, manifested as discrete two-level current fluctuations between 90-150 K arising from
stochastic trapping at localized hBN defect sites. With increasing temperature, the RTN evolves into a 1/f spectrum as multiple traps activate. Statistical analysis of RTN amplitudes and capture-emission kinetics identifies substitutional carbon-related centers in hBN as dominant defects. These findings establish a generalizable approach for probing dielectric-origin defect dynamics in intrinsically conducting, low-
symmetry 2D
semiconductors.
Read the full abstract ▾
All authors Shubhrasish Mukherjee, Gaurab Samanta, Shubhadip Moulick, Ruta Kulkarni, Kenji Watanabe, Takashi Taniguchi, Arumugum Thamizhavel, Atindra Nath Pal
Materials Science
Effect of temperature and excitation power on down-conversion process in Tb3+/Yb3+-activated silica-hafnia glass-ceramic films
S. E. Amrani, M. Sun, S. Valdueza-Felip et al. (+4 more)
Transparent glass ceramics, when activated by rare earth ions, are excellent photonic materials. Regarding photonic glass-ceramics based on silicates, hafnia and silica in a binary system has proved to be an excellent
matrix to incorporate rare earth ions in the hafnia nanocrystals, resulting in important luminescence enhancement and, consequently, allowing a large spectrum of critical applications. Here we will focus on the downconversion mechanism driven by the couple Tb3+/Yb3+, largely exploited in photovoltaic systems. The research presented here has been performed on 70SiO2-30HfO2 silica-hafnia glass-ceramic films activated with 19 % rare earth ions: [Tb + Yb]/[Si + Hf] = 19 %. Two main results will be discussed: (a) the intensity and the broadening of the Yb3+ emission band at 975 nm were found to be temperature-dependent, as shown in the figure; (b) the energy transfer mechanism Tb3+ >> Yb3+ will be discussed, referring to the mechanisms that have been proposed in the literature. In relation to the latter topic, the power dependence spectra for the luminescence of Yb3+: 2F5/2 >> 2F7/2 will be discussed.
Read the full abstract ▾
All authors S. E. Amrani, M. Sun, S. Valdueza-Felip, F. B. Naranjo, M. R. Britel, M. Ferrari, A. Bouajaj