Statistical Mechanics
Necessary conditions for the Markovian Mpemba effect
Ido Avitan, Roee Factor and David Gelbwaser-Klimovsky
The Mpemba effect is a thermodynamic anomaly in which a system farther away in temperature from
equilibrium thermalizes before one that is initially closer. The effect has been experimentally observed across a wide range of systems, including water, colloids, and trapped ions. It has recently been the focus of numerous studies aimed at understanding its mechanisms and developing multiple applications. Despite extensive work in the field, clearly determining which types of systems exhibit the Mpemba effect remains an open question. To address this, we derive simple necessary conditions on the transition rates for the Mpemba effect in a Markovian 3-level system and show that they can be applied to study the Mpemba effect in an N-level system. Multiple time scales govern thermalization in these systems. This allows the
evolution to occur more quickly across larger temperature differences, explaining the Mpemba effect. We apply our protocol to evaluate which types of systems exhibit the Mpemba effect and, in doing so, explain why the Mpemba effect in Markovian systems remains a thermodynamic anomaly. In particular, due to the maximum
entropy principle, our conditions allow us to discard the sub-Ohmic and Ohmic spectra. The latter describes a wide range of physical and chemical phenomena, which will not exhibit the Mpemba effect. Moreover, our results provide a clear path to determine the minimal physical requirements for the Mpemba effect, and we apply them to understand its underlying mechanisms better. Finally, our protocol could help identify relevant parameters for experiments, numerical simulations and diverse applications.
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Statistical Mechanics · Cross-listed from physics.chem-ph
How to improve the accuracy of semiclassical and quasiclassical dynamics with and without generalized quantum master equations
Matthew R. Laskowski, Srijan Bhattacharyya and Andrés Montoya-Castillo
Semi- and quasi-classical (SC) theories can handle arbitrary interatomic interactions and are thus well-suited to predict
quantum dynamics in condensed phases that encode energy and charge transport, spectroscopic responses, and chemical reactivity. However, SC theories can be computationally expensive and inaccurate. When combined with generalized
quantum master equations (GQMEs), the resulting SC-GQMEs have been observed to enhance the efficiency and accuracy of SC dynamics. Yet, while the mechanism responsible for improved efficiency is clear, the underlying improved accuracy remains elusive. What is worse, SC-GQMEs can yield unphysical dynamics in challenging parameter regimes – a shortcoming that might be avoided if the mechanism of accuracy improvement were understood. Here, we uncover this mechanism. We leverage short-time analyses to prove that exact, "left-handed" time-derivatives delay the onset of SC inaccuracy, and show that their numerical integration yields dynamics with improved accuracy, even without the GQME. We find, however, that these derivatives are a double-edged sword: while offering greater short-time accuracy, they become unphysical in challenging parameter regimes. Because short-lived
memory kernels can leverage short-time accuracy while circumventing long-time instability, we develop a protocol to unambiguously determine the
memory kernel cutoff, even in challenging regimes where previous treatments had failed. Our insights into accuracy improvement and kernel cutoff protocol can be expected to apply to complex systems that go beyond simple models.
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Materials Science
Raman scattering spectroscopic observation of a ferroelastic crossover in bond-frustrated PrCd$_3$P$_3$
Jackson Davis, Jesse Liebman, Dibyata Rout et al. (+3 more)
2D magnetism in triangular
lattices has already shown potential for hosting exotic
magnetic states. Control of these
magnetic states, both in terms of
magnetic properties and in terms of charge doping would be the next step. This makes materials which combine triangular
lattice magnetic layers with layers hosting interesting structural or electronic properties particularly useful. PrCd$_3$P$_3$, studied in this work, is one of a family of materials where triangular
lattice layers of
magnetic rare earth ions alternate with semiconducting hexagonal CdP layers. Using Raman scattering spectroscopy we uncover a structural instability in the CdP layers, associated with a soft mode behavior of a
phonon in these layers. Raman scattering detects
crystal electric field excitations, and confirms a singlet ground state for Pr$^{3+}$ and splitting of the doublet levels as a result of the structural instability in CdP layers. While Pr$^{3+}$ is non-
magnetic in PrCd$_3$P$_3$ we speculate that this family of materials can realize control of the
magnetic layer through the CdP layer which can become ferroelectric under strain that would relieve frustration.
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All authors Jackson Davis, Jesse Liebman, Dibyata Rout, S.J. Gomez Alvarado, Stephen D. Wilson, Natalia Drichko
Mesoscale and Nanoscale Physics
Heat Capacity Anomalies and Thermal Crossovers in Finite Su-Schrieffer-Heeger Chains
Carlos Magno da Conceição, Julio César Pérez-Pedraza, Alfredo Raya et al. (+1 more)
We investigate the thermodynamic properties of finite Su-Schrieffer-Heeger (SSH) chains in thermal
equilibrium at fixed temperature and chemical potential. Using the canonical and grand canonical ensembles, we calculate the energy density, particle number density,
entropy, and heat capacity as functions of temperature, chemical potential, and hopping asymmetry. Our analysis reveals a double-peak anomaly in the heat capacity for non-dimerized configurations, in which two maxima are separated by a local minimum. We identify this feature as a Schottky-type thermal crossover governed by two distinct energy scales. The anomaly is most pronounced when the chemical potential is comparable to the band scale, and its two maxima separate further as the hopping asymmetry increases and the chain length grows, reflecting the widening gap between the two energy scales and the increasing density of states. We demonstrate that while the topological properties are determined by boundary states, the bulk thermodynamic behavior exhibits a rich crossover structure that can be tuned through the hopping parameter ratio. These findings provide insights into the interplay between
topology, finite-size effects, and thermal fluctuations in one-dimensional topological systems, with potential implications for experimental realizations in cold atoms, photonic systems, and topoelectrical
circuits.
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All authors Carlos Magno da Conceição, Julio César Pérez-Pedraza, Alfredo Raya, Cristian Villavicencio
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Markovian quantum master equations are exponentially accurate in the weak coupling regime
Johannes Agerskov and Frederik Nathan
We consider the
evolution of open
quantum systems coupled to one or more Gaussian environments. We demonstrate that such systems can be described by a Markovian
quantum master equation (MQME) up to a correction that decreases exponentially with the inverse system-bath coupling strength. We provide an explicit expression for this MQME, along with rigorous bounds on its residual correction, and numerically
benchmark it for an exactly solvable model. The MQME is obtained via a generalized Born-Markov approximation that can be iterated to arbitrary orders in the system-bath coupling; our error bound converges asymptotically to zero with the iteration order. Our results thus demonstrate that the non-Markovian component in the
evolution of an open
quantum system, while possibly inevitable, can be exponentially suppressed at weak coupling.
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Superconductivity
Superconducting States and Intertwined Orders in Metallic Altermagnets
Xuan Zou, Rafael M. Fernandes and Eduardo Fradkin
Altermagnets are a newly identified class of magnets with nodal
spin-split band structures, providing a fertile platform for studying unconventional superconductivity and intertwined orders. Here we investigate multicomponent superconductivity and fluctuation-induced intertwined orders in an interacting $d$-wave metallic altermagnet that is invariant under a combination of a fourfold rotation $C_4$ and time-reversal
symmetry $T$. Within mean-field theory, the superconducting ground-state
manifold is described in terms of two equal-
spin two-component $p$-wave gap functions $(\Delta_A^x,\Delta_B^y)$ and $(\Delta_A^y,\Delta_B^x)$, where $A$ and $B$ refer to the two
spin-polarized
Fermi surfaces related by $C_4T$
symmetry. Because these two sets of gap functions condense at different temperatures, a rich phase diagram with multiple superconducting phase transitions emerges. Distinct fluctuations of sub-leading normal-state instabilities that compete with altermagnetism lift the degeneracy of the multicomponent pairing state in different ways. While nematic fluctuations enhance competition between distinct superconducting components and stabilize nematic superconducting phases,
spin current-loop fluctuations promote coexistence and select a pair of
chiral states. Our results uncover the pairing structure and elucidate how intertwined sub-leading fluctuations shape superconducting order in altermagnetic metals, suggesting a route toward realizing nematic and topological superconductivity.
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Other Condensed Matter · Cross-listed from quant-ph
Fundamental Limits on Polarization Entanglement Distribution in Optical Fiber
Stefano Pirandola
Characterizing the ultimate rates of
entanglement distribution is essential for both foundational research and the practical deployment of
quantum technologies. To investigate these limits, we introduce an erasure-Pauli channel model describing the distribution of polarization
entanglement in optical fiber. For this channel, we derive bounds on the rates of
entanglement distribution and related
quantum resources under optimal local operations and two-way classical communication (two-way assisted capacities). This framework allows us to determine the optimal repeaterless performance achievable over realistic optical fibers affected by polarization mode dispersion, thereby providing a rigorous
benchmark for long-distance polarization-based
quantum communication. Finally, we show that both our model and capacity bounds remain robust under the inclusion of detector dark counts.
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Mesoscale and Nanoscale Physics
Ge as an orbitronic platform: giant in-plane orbital magneto-electric effect in a 2-dimensional hole gas
James H. Cullen and Dimitrie Culcer
Increasing demand for computational power has initiated the hunt for energy efficient and stable
memory devices. This is the overarching motivation behind the recent rise of orbitronics, which looks to harness the orbital angular momentum of charge carriers in computing devices. Orbitronic devices require materials with efficient generation of orbital angular momentum (OAM). In 2D materials, OAM can be electrically generated via the orbital magneto-electric effect (OME). In this paper we report the calculation of the OME in 2 dimensional hole gases (2DHGs). We show that the OME in Ge holes is very large, for an applied electric field of the order $10^4$ V$/$m the OAM density is of the order $10^{12}$ $\hbar/$cm$^{2}$. Furthermore, we find the OME to be an order of magnitude larger than the Rashba-Edelstein effect in 2DHGs. The OME we calculated in 2DHGs generates OAM aligned in the plane and arises due to transitions between heavy and light hole states, which is unique to this system. Our results put Ge, as well as other p-type
semiconductors, forward as strong candidates for building future orbitronic devices.
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Quantum Gases
Chiral and pair superfluidity in triangular ladder produced by state-dependent Kronig-Penney lattice
Domantas Burba, Giedrius Žlabys, Dzmitry Viarbitski et al. (+2 more)
We propose a concrete realization of a triangular ladder for ultracold atoms, which simultaneously hosts
geometric frustration and unusual two-body interactions, and in particular controllable pair hopping and density-induced tunneling. This is done by means of a
spin-dependent Kronig-Penney
lattice created using a spatially-dependent tripod-type atom-light coupling. We apply density
matrix renormalization group (DMRG) calculations to derive the
quantum phase diagram. We find that pair tunneling stabilizes a robust pair superfluid, characterized by power-law decay of pair correlations. Additionally, a
chiral superfluid arises from frustration induced by competing nearest neighbor (NN) and next-nearest neighbor (NNN) tunnelings. Finally, in the high barrier regime, we map our system onto the XXZ
spin model and find the exact phase transition points.
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All authors Domantas Burba, Giedrius Žlabys, Dzmitry Viarbitski, Thomas Busch, Gediminas Juzeliūnas
Strongly Correlated Electrons
Giant Magnetocrystalline Anisotropy in Honeycomb Iridate NiIrO3 with Large Coercive Field Exceeding 17 T
Chuanhui Zhu, Pengfei Tan, Xiao-Sheng Ni et al. (+13 more)
The realization of unconventional
quantum phases in frustrated and
spin-orbit coupled materials remains at the forefront of
quantum materials research. Here we report the synthesis and discovery of NiIrO3, the first honeycomb iridate with coupled 3d-5d
magnetic sublattices, through a soft topotactic reaction. Structural analysis reveals an ilmenite-type stacking of edge-sharing NiO6 and IrO6 octahedral honeycomb sublattices in a Kitaev geometry. Comprehensive
magnetic and electrical transport measurements unveil its long-range ferrimagnetic order below 213 K, which is in sharp contrast to the predominantly
antiferromagnetic order in the known honeycomb iridates. Notably, the titled compound displays an exceptionally large magnetocrystalline anisotropy energy of 32.2 meV/f.u. and a
giant coercivity with coercive field exceeding 17.3 T below 4.2 K, both ranking among the highest observed in iridates to date. Combined experimental and theoretical investigations indicate that the exceptional anisotropy and coercivity originate from the synergistic effect between strong
lattice frustration in the coupled 3d-5d honeycomb
lattice network and the robust
spin-orbit coupling of the Ir4+ (Jeff = 1/2) state. This work positions NiIrO3 as a promising platform to investigate low-dimensional and frustrated
quantum spin systems, and highlights its potential for spintronic applications through the targeted engineering of 3d-5d interactions.
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All authors Chuanhui Zhu, Pengfei Tan, Xiao-Sheng Ni, Jingchun Gao, Yuting Chang, Mei-Huan Zhao, Zheng Deng, Shuang Zhao, Tao Xia, Jinjin Yang, Changqing Jin, Junfeng Wang, Chengliang Lu, Yisheng Chai, Dao-Xin Yao, Man-Rong Li
Disordered Systems and Neural Networks · Cross-listed from physics.optics
Realizing anomalous Floquet non-Abelian band topology in photonic scattering networks
Yuze Hu, Mingyu Tong, Tian Jiang et al. (+10 more)
The concept of multi-gap
topology has recently been shown to give rise to uncharted phases beyond conventional single-gap classifications. These phases relate to band nodes with non-Abelian quaternion charges and momentum-space braiding processes characterized by new invariants such as paradigmatic Euler class, phenomena that intrinsically require at least two spatial dimensions. Extending such phases into the non-
equilibrium regime is predicted to unlock even richer multi-gap
topologies beyond static settings, yet their experimental realization has remained elusive due to the stringent requirements on dimensionality,
symmetry, and dynamical control. Here, we theoretically demonstrate and, for the first time, experimentally realize two-dimensional (2D) Floquet non-Abelian band
topology in photonic scattering networks. Within this platform, we uncover a sequence of topological phenomena unique to 2D multi-gap systems far from
equilibrium, including anomalous multi-gap phases interconnected by band nodes, Floquet Euler transfer, gapped phases with anomalous Dirac string configurations, and Floquet-induced non-Abelian braiding of band nodes. In addition, we observe Floquet-periodic anomalous edge states across multiple gaps, providing experimental signatures of these sought-after 2D multi-gap Floquet topological phases. Our results establish photonic scattering networks as a practical and versatile route to non-Abelian Floquet systems, opening avenues for dynamical topological physics with braiding capability and robust photonic functionalities.
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All authors Yuze Hu, Mingyu Tong, Tian Jiang, Shuxing Yang, Ning Han, Fujia Chen, Li Zhang, Rui Zhao, Qiaolu Chen, Hongsheng Chen, F. Nur Ünal, Robert-Jan Slager, Yihao Yang
Statistical Mechanics · Cross-listed from quant-ph
Unified Probe of Quantum Chaos and Ergodicity from Hamiltonian Learning
Nik O. Gjonbalaj, Christian Kokail, Susanne F. Yelin et al. (+1 more)
Developing measures of
quantum ergodicity and chaos stands as a foundational task in the study of
quantum many-body systems. In this work, we propose metrics for these effects based on
Hamiltonian learning that unify multiple advantages of existing metrics. In particular, we show how ergodicity and chaos improve the robustness of
Hamiltonian learning to small errors and furthermore demonstrate that this robustness can be used as a metric for such phenomena. We analytically and numerically show that our metrics not only distinguish between integrable and ergodic regimes in various
spin chains but also quantify chaos and ergodicity, allowing us to locate regions of parameter space displaying maximal ergodicity and maximal sensitivity to local perturbations. Our approach not only provides conceptual ways to study
quantum chaos and ergodicity but also presents viable experimental methods for
quantum simulators.
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All authors Nik O. Gjonbalaj, Christian Kokail, Susanne F. Yelin, Soonwon Choi
Mesoscale and Nanoscale Physics
Coherent Biexciton Transport in the Presence of Exciton-Exciton Annihilation in Molecular Aggregates
Rajesh Dutta and Chern Chuang
We present a theoretical framework for biexciton dynamics in molecular aggregates that explicitly treats populations and coherences across excitation
manifolds within a reduced density-
matrix formalism. By extending kinetic descriptions beyond the weak-coupling limit, the approach captures the influence of
exciton delocalization and
exciton-
exciton annihilation while remaining computationally tractable within a Markovian description of environmental relaxation. Using this framework, we investigate how the spatial profile and momentum composition of the initial biexciton state govern fluorescence decay and transport. Incoherent initial conditions lead to strongly non-exponential relaxation and time-dependent
diffusion driven by nonlinear population kinetics. In contrast, coherently prepared biexciton states exhibit pronounced early-time coherent transport, whose character depends sensitively on whether the initial state is prepared as a standing-wave or traveling-wave superposition of single-
exciton modes. Despite nearly identical emission dynamics for J and H aggregate, biexciton transport properties differ markedly due to band structure-dependent interference effect. Our results demonstrate that biexciton dynamics remains strongly influenced by initial-state coherence and momentum composition. Besides initial-state preparation, the coherent-to-incoherent crossover and the diffusive spreading of the
exciton density are sensitive to internal conversion processes such as
exciton fusion and the decay to the first excited state. The present work establishes initial-state preparation as a key control parameter for many-
exciton transport in excitonic systems and provides a general framework for interpreting nonlinear optical experiments beyond population-based descriptions.
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Disordered Systems and Neural Networks · Cross-listed from physics.optics
Hyperuniform Disorder in Photonic Crystal Slabs with Intrinsic non-Hermiticity
Zeyu Zhang, Koorosh Sadri, Brian Gould et al. (+1 more)
Hyperuniform disorder is a type of correlated disorder characterized by vanishing spectral density at small wavevectors, making the configuration effectively homogeneous on long length scales. In photonics, hyperuniform disorder is promising for generating isotropic photonic pseudogaps and engineering photonic
crystal waveguides. However, these studies are largely restricted to idealized lossless settings, although all photonic systems necessarily have loss. In this work, light propagation in photonic
crystal slabs with imposed hyperuniform disorder is investigated theoretically and numerically. The system is intrinsically non-Hermitian due to radiative loss, with non-Hermiticity appearing as a complex effective mass of a quadratic photonic band. A theoretical framework for disorder scattering is analytically derived in Hermitian and non-Hermitian quadratic bands with real and complex effective mass, respectively. In contrast to the power law behavior $|\mathbf{k}|^\alpha$ observed in the Hermitian case (where $\alpha$ is the hyperuniformity exponent), the scattering loss in the non-Hermitian band is given by $C_0+C_{\beta_2}\cdot|\mathbf{k}|^{\beta_2}$, where $C_0$ is a finite constant and the exponent $\beta_2\leq 2$. Our theoretical predictions are verified with tight-binding and Finite-Difference Time-Domain simulations with realistic photonic
crystal parameters, based on recent experiments.
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All authors Zeyu Zhang, Koorosh Sadri, Brian Gould, Mikael Rechtsman
Soft Condensed Matter
Dynamic properties in a collisional model for confined granular fluids. A review
Ricardo Brito, Rodrigo Soto and Vicente Garzó
Granular systems confined in a shallow box and driven by vertical vibration provide a simple geometry to study fluidized granular media. Grains gain kinetic energy vertically through collisions with the walls and redistribute it horizontally via interparticle collisions. The $\Delta$-model has been proposed as a simplified description of this setup. In this model, a fixed velocity increment $\Delta$ is added to the normal component of the relative velocity at collisions, effectively integrating out the vertical motion while preserving collisional energy injection. This compensates for inelastic losses and yields stable homogeneous steady states amenable to kinetic theory. An Enskog kinetic equation is formulated and analyzed to obtain the stationary temperature and equation of state. The Chapman–Enskog method is then applied to derive the Navier–Stokes transport coefficients and study inhomogeneous states. The theory is extended to granular mixtures with different masses, sizes, restitution coefficients, or $\Delta$ values, leading to nonequipartition of energy even in homogeneous states. The resulting hydrodynamic equations, with transport coefficients obtained in the low-density regime, show unconditional stability of the homogeneous state and violation of Onsager reciprocity. Theoretical predictions agree well with molecular dynamics and direct simulation Monte Carlo results.
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Quantum Gases · Cross-listed from quant-ph
Dynamical Behaviour of Density Correlations Across the Chaotic Phase for Interacting Bosons
Óscar Dueñas and Alberto Rodríguez
We investigate the propagation of two-point density correlations in the one-dimensional Bose-Hubbard
Hamiltonian in the thermodynamic limit in terms of the correlation transport distance (CTD), an experimentally measurable magnitude that characterizes the spatial spreading of correlations in time. We confirm that the integrable limits of the model exhibit CTD ballistic growth, while the onset of the chaotic phase leads to the emergence of a pronounced sub-ballistic regime, in agreement with previous results for finite systems. By a meticulous analysis of the spatio-temporal correlation profiles, we show that the correlation front nonetheless propagates ballistically for all interaction strengths, and that the chaos-induced slowdown of the CTD originates from the emergence of long-time distance-dependent correlation tails, together with an enhanced decay of the correlation front amplitude. Our results thus provide a detailed characterization of correlation transport that goes beyond a simple light-cone picture.
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Materials Science · Cross-listed from cs.RO
A Soft Robotic Demonstration in the Stratosphere
Codrin Tugui, Tirth Thakar, Anatol Gogoj et al. (+5 more)
Machines designed for operation in Space, as well as other extreme environments, need to be both resilient and adaptable when mission parameters change. Soft
robots offer advantages in adaptability, but most lack resilience to the pressure and temperature extremes found as close as the Stratosphere. Dielectric elastomer actuators overcome some of those limitations when built as solid state compliant capacitors capable of converting electrical energy into mechanical work, but the elastomer resilience limits the device's operating window. Here we present a crosslinking mechanism for silicone elastomers under ultraviolet light using trimethyl(methylcyclopentadienyl)platinum(IV) as a catalyst to react hydrosilane to vinyl groups. The formation of carbon-carbon bonds enables fast processing under UV light and exceptional electro-mechanical performance in dielectric elastomer actuators. The material resilience advantage is demonstrated in controlled experiments at -40{\deg} and 120{\deg} C, as well as near
vacuum, in comparison with state-of-the-art acrylic and silicone chemistries. Fully autonomous systems controlling grippers made with the novel silicone were integrated into payloads for high altitude balloon testing. Two stratospheric balloon missions were carried out and demonstrated DEAs as a viable soft robotic technology under space-like conditions (as high as 23.6 km elevation, at <0.05 atm and -55{\deg} C). The combinations of chemical building blocks and catalyst can be further expanded to address other challenges for silicones, including adhesion and additive manufacturing.
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All authors Codrin Tugui, Tirth Thakar, Anatol Gogoj, Alexander White, Ang Leo Li, Alexander Yin, Edward Pomianek, Mihai Duduta
Materials Science
Study on the Effect of Annealing on Ga$_2$O$_3$ Thin Films Deposited on Silicon by RF Sputtering
Ana Sofia Sousa, Duarte M. Esteves, Tiago T. Robalo et al. (+3 more)
Gallium
oxide is an ultra-wide bandgap
semiconductor with excellent opto-electronic properties, making it a highly promising material for a wide range of applications and devices. In this article, we report how the optical, morphological, structural, and compositional properties of $\beta$-Ga$_2$O$_3$ thin films deposited by RF sputtering on silicon substrates are affected by thermal treatments. Ellipsometric spectra recorded at multiple angles of incidence from several samples subjected to thermal annealing in the range of 550-1000 $^\circ$C were analyzed to extract the optical functions using appropriate multilayer models. This analysis is complemented by compositional, structural, and morphological characterization techniques. A significant increase of the refractive index was found after annealing at 1000 $^\circ$C, accompanied by a stark improvement in the samples' crystalline structure, as confirmed by complementary structural and compositional characterization techniques.
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All authors Ana Sofia Sousa, Duarte M. Esteves, Tiago T. Robalo, Mário S. Rodrigues, Katharina Lorenz, Marco Peres
Mesoscale and Nanoscale Physics
Sub-wavelength mid-infrared imaging of locally driven photocurrents using diamond campanile probes
Rajasekhar Medapalli, Nathan D. Cottam, Khushboo Agarwal et al. (+12 more)
Precise and high efficiency concentration of mid-infrared (mid-IR) light into sub wavelength volumes is essential for probing low-energy excitations and achieving strong field enhancements, which can be hindered by absorption losses and coupling inefficiencies at long wavelengths. Here, we introduce an innovative diamond-based metal-
insulator-metal campanile probe that adiabatically compresses free-space mid infrared light (10 \mum) into \approx 1 \mum domains. Integrated into a scanning photovoltage microscope, the probe enables sub-wavelength mapping of locally driven photocurrents in
graphene, resolving polarization dependent and contact-sensitive responses at energies down to \approx 0.1 eV. Experiments reveal a photocurrent signal density enhancement of 10^3 and coupling efficiencies approaching 80%, in agreement with numerical simulations. Operation of the probe with
quantum cascade and free electron
lasers demonstrates a robust, spectrally tunable platform for high-resolution exploration of low-energy carrier dynamics in atomically thin materials, opening opportunities for mid-IR optoelectronics and
quantum photonics.
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All authors Rajasekhar Medapalli, Nathan D. Cottam, Khushboo Agarwal, Benjamin T. Dewes, Nils Dessmann, Sergio Gonzalez-Munoz, Wenjing Yan, Vaidotas Mišeikis, Sergey Kafanov, Rostislav V. Mikhaylovskiy, Samuel P. Jarvis, Camilla Coletti, Britta Redlich, Amalia Patanè, Oleg V. Kolosov
Mesoscale and Nanoscale Physics
Hanle lineshapes and spin-rotation signatures from in-plane anisotropic spin relaxation in heterogeneous spin devices
Josef Světlík, Juan F. Sierra, Lorenzo Camosi et al. (+5 more)
Spin precession experiments in lateral
spin devices are a powerful tool for probing the
spin transport properties of materials. These experiments can be quantitatively described using the Bloch
diffusion equation, which offers a practical framework for modeling
spin-related phenomena. In this work, we present calculations of the
spin density across heterogeneous, diffusive spintronic devices. The modeled devices feature
spin transport channels that include both isotropic and in-plane anisotropic
spin relaxation regions. We analyze how different
geometric configurations and
spin transport parameters influence the lineshape of
spin precession signals under
magnetic fields applied in different orientations and compare with experimental observations. Our results introduce a theoretical framework for interpreting
spin transport measurements in lateral
graphene spin devices. The framework is especially relevant when the
graphene is partially proximitized by other two-dimensional materials, where proximity-induced
spin-orbit coupling leads to anisotropic
spin relaxation.
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All authors Josef Světlík, Juan F. Sierra, Lorenzo Camosi, Williams Savero Torres, Franz Herling, Vera Marinova, Dimitre Dimitrov, Sergio O. Valenzuela
Mesoscale and Nanoscale Physics
Ab initio study of saddle-point excitons in monolayer SnS2
Vinicius Alves Bastos, Fulvio Paleari, Eleonora Luppi et al. (+2 more)
Monolayer SnS2 has emerged as a promising visible-light photocatalyst for photoelectrochemical applications, owing to its strong optical absorption in the visible range and excellent chemical stability. Despite its reduced dimensionality - where excitonic effects are expected to be pronounced - comprehensive theoretical investigations of bound
excitons in this material remain scarce. Notably, unlike most two-dimensional hexagonal
crystals, monolayer SnS2 exhibits its lowest single-particle transition at the M point of the Brillouin zone (BZ). Here, the electronic valence bands form a saddle point while conduction states display a minimum with pronounced anisotropy, creating a distinctive band
topology whose impact on optical excitations has not yet been systematically explored. In this work, we present a first-principles study of bound
excitons in monolayer SnS2 based on state-of-the-art many-body perturbation theory, employing the GW approximation and the Bethe-Salpeter equation (BSE). We analyze how band
symmetry and anisotropy shape the excitonic wavefunctions and transition dipole moments. By resolving the
exciton dipoles in momentum space for different linear light polarizations, we demonstrate that linearly polarized light lifts the C3 rotational
symmetry relating the three inequivalent M points, giving rise to three linearly independent excitonic states. This polarization-selective coupling, previously identified for saddle points in
graphene, is achieved in SnS2 for bound
excitons and provides a potential route toward state encoding schemes in valleytronics applications.
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All authors Vinicius Alves Bastos, Fulvio Paleari, Eleonora Luppi, Marco Gibertini, Alice Ruini
Materials Science
The effect of chemical vapor infiltration process parameters on flexural strength of porous {\alpha}-SiC: A numerical model
Joseph J. Marziale, Jason Sun, Eric A. Walker et al. (+3 more)
The flexural strength variability of {\alpha}-SiC based ceramics at elevated temperatures creates the need for an Integrated Computational Materials Engineering (ICME) framework that relates the strength of a specimen directly to its manufacturing process. To create this ICME framework a model must first be developed which establishes a relationship between the chemical vapor infiltration (CVI) process and parameters, the resulting mesoscale pores, and the overall macroscale flexural strength. Here a nonlinear single pore model of CVI is developed used in conjunction with a four-way coupled themo-mechanical damage model. The individual components of the model are tested and a sample system under a four-point bending test is explored. Results indicate that specimens with an initial porosity greater than 30% require temperatures below 1273 K to maintain structural integrity, while those with initial porosities less than 30% are temperature-independent, allowing for optimization of the CVI processing time without compromising strength.
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All authors Joseph J. Marziale, Jason Sun, Eric A. Walker, Yu Chen, David Salac, James Chen
Statistical Mechanics
Kinetic Theory of Chiral Active Disks: Odd Transport and Torque Density
Raphael Maire, Alessandro Petrini, Umberto Marini Bettolo Marconi et al. (+1 more)
Parity-odd transport is a central signature of
chiral fluids, yet analytical predictions are sparse. Here, we introduce a minimal two-dimensional hard-disk gas in which chirality arises solely from a collision-induced transverse impulse. Motivated by granular spinners, collisions are dissipative and inject orbital angular momentum through a fixed tangential “kick” at contact. Starting from a Boltzmann-Enskog description, we derive nonlinear hydrodynamic equations for density, momentum, and temperature, and show that chirality generates an antisymmetric homogeneous stress corresponding to a nonzero torque density. In the dilute limit, a Chapman-Enskog expansion yields analytical predictions for transport coefficients, including odd viscosity, odd thermal conductivity, and odd self-diffusivity, in good agreement with numerical simulations. This minimal kinetic model can serve as a foundation for systematic coarse-graining of
chiral fluids and as a tractable
benchmark for gaining insight into odd transport across a broader class of
chiral systems.
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All authors Raphael Maire, Alessandro Petrini, Umberto Marini Bettolo Marconi, Lorenzo Caprini
Strongly Correlated Electrons
Dimensional reduction by singlet blockade in the distorted kagome magnet YCa$_3$(CrO)$_3$(BO$_3$)$_4$
Umashankar Jena, Satish Kumar, Harald O. Jeschke et al. (+3 more)
The distorted kagome borate YCa$_3$(CrO)$_3$(BO$_3$)$_4$ has a Curie-Weiss temperature of -140 K and shows no
magnetic order down to $65$ mK. We determine its Heisenberg
Hamiltonian by density-functional energy mapping, obtaining twenty-four
symmetry-inequivalent Cr-Cr exchange paths dominated by $J_1=116$ K, and measure the susceptibility, specific heat and ac susceptibility to $50$ mK. The
Hamiltonian does not by itself account for the absence of order: simulated classically it orders at $10$ K, a factor of $154$ above the bound. We trace the gap to the site
symmetry of the $P6_3$ structure, which divides the exchange network in two: $J_1$ binds two thirds of the Cr into dimers, while the remaining third forms uniform
spin-$3/2$ chains along $c$ through a weaker $J_2=33$ K. The chains share no direct bond, and each of the fourteen paths leaving a chain terminates on a
spin locked into a dimer singlet of gap $\Delta=J_1$. This singlet blockade demotes the interchain coupling to second order; summed over paths with their relative Néel parity it falls to a few tens of millikelvin, against $9.8$ K at first order, and what survives is frustrated on the kagome
lattice the chains themselves form. Treating the dimers exactly and the chains by exact diagonalization accounts, without free parameters, for the position of the
magnetic specific-heat maximum and the
entropy recovered by $100$ K, but not for the susceptibility, which additionally requires a broad distribution of exchange couplings that we attribute to Ca/Y site mixing. That disorder also impacts the thermodynamics at lowest temperatures: below $0.7$ K the
magnetic specific heat follows a field-robust $T^2$ law, which excludes one-dimensional chains with gapless excitations, Goldstone modes and spinons alike and implies a linear density of predominantly non-
magnetic states, matched by the singlet-triplet gaps the disorder generates.
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All authors Umashankar Jena, Satish Kumar, Harald O. Jeschke, G. B. G. Stenning, Panchanana Khuntia, Yasir Iqbal
Disordered Systems and Neural Networks
Predicting oscillations in complex networks with delayed feedback
Shijie Liu, Jinliang Han, Jianming Liu et al. (+2 more)
Oscillatory dynamics are common features of complex networks, often playing essential roles in regulating function. Across scales from gene regulatory networks to ecosystems, delayed feedback mechanisms are key drivers of system-scale oscillations. The analysis and prediction of such dynamics are highly challenging, however, due to the combination of high-dimensionality, non-linearity and delay. Here, we systematically investigate how structural complexity and delayed feedback jointly induce oscillatory dynamics in complex systems, and introduce an analytic framework comprising theoretical dimension reduction and data-driven prediction. We reveal that oscillations emerge from the interplay of structural complexity and delay, with reduced models uncovering their critical thresholds and showing that greater connectivity lowers the delay required for their onset. Our theory is empirically tested in an experiment on a programmable electronic
circuit, where oscillations are observed once structural complexity and feedback delay exceeded the critical thresholds predicted by our theory. Finally, we deploy a reservoir computing pipeline to accurately predict the onset of oscillations directly from timeseries data. Our findings deepen understanding of oscillatory regulation and offer new avenues for predicting dynamics in complex networks.
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All authors Shijie Liu, Jinliang Han, Jianming Liu, Tim Rogers, Yongzheng Sun
Mesoscale and Nanoscale Physics
Progress on artificial flat band systems: classifying, perturbing, applying
Carlo Danieli and Sergej Flach
We highlight recent progress in the study of artificial flat band systems with a threefold focus. First, we discuss single-particle flat band physics, which has advanced through the design of various flat band generators. These generators rely on the classification of flat bands in terms of compact localized states - their fundamental building blocks. A related development is the complete real-space description of flat band projectors. Next, we review studies on perturbations of flat bands, which provide new insights into the effects of disorder and, more importantly, the intricate interplay between many-body interactions and flat band physics. Finally, we survey the growing number of experimental realizations of flat bands across diverse physical platforms.
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Disordered Systems and Neural Networks
Non-equilibrium dynamics of the disordered Power of Two model
Kunal Singh and Sayan Choudhury
Motivated by recent experimental realizations of programmable
spin models with long-range interactions, we investigate the non-
equilibrium dynamics of the Power-of-Two (PWR2) model. This model consists of sparse long-range couplings between
spin-$1/2$ objects separated by $d = 2^n$. In the absence of disorder, the system exhibits rapid scrambling and fast thermalization. We explore the impact of disorder in this system by analyzing the time
evolution of the survival probability, half-chain
entanglement entropy, and out-of-time-ordered correlators (OTOCs). We find that sufficiently strong disorder suppresses information spreading and induces localization. Remarkably, in the strong-disorder regime, the OTOCs display a non-monotonic spatial profile arising from the intrinsic nonlocality of the interactions, signaling qualitatively distinct scrambling dynamics compared to conventional long-range interacting systems. To characterize the localization transition, we extract the critical disorder strength $h_c$ from the spectral statistics and the eigenstate
entanglement. We observe that $h_c$ increases with system size. Furthermore, at a fixed disorder strength, the eigenstate-averaged
entanglement entropy increases with system size, while the inverse participation ratio decreases, indicating enhanced delocalization at larger sizes. These results collectively suggest that the PWR2 model remains ergodic in the thermodynamic limit for any finite disorder strength.
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Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Graphs as focal interaction systems in higher-order dynamics
Elkaïoum M. Moutuou
Graphs and hypergraphs are commonly distinguished by the order of the relations they represent, with graphs encoding pairwise relations and hypergraphs encoding interactions among arbitrary groups. We show that, for node-update dynamics, a more natural viewpoint is to regard a graph as a collection of focal neighbourhoods, each centered on a vertex and consisting of the vertex and its neighbours. From this perspective, hypergraphs naturally generalise graph neighbourhoods by allowing arbitrary interaction domains without requiring a distinguished focal node. This viewpoint also clarifies the relationship between graph and hypergraph dynamical models. Although sufficiently general graph-based node functions can reproduce the dynamics of higher-order interactions, such dynamical equivalence does not imply equivalence of the underlying interaction structures. Graph representations may encode higher-order organisation implicitly in their functions while losing the explicit grouping, roles, and
symmetries carried by hyperedges. We therefore distinguish dynamical expressivity from structural representation and show that hypergraphs provide a generalisation of graph-based interaction domains even when their dynamics can be emulated by graph models.
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Quantum Gases · Cross-listed from quant-ph
Constructing Arbitrary Coherent Rearrangements in Optical Lattices
Alexander Roth, Liyang Qiu, Timon Hilker et al. (+2 more)
Coherent control of motional degrees of freedom of ultracold atoms in optical
lattices offers a promising route towards programmable
quantum dynamics with massive particles. We propose and analyze a scheme for implementing coherent rearrangement of ultracold atoms, corresponding to arbitrary
unitary transformations on single-particle motional states. Exploiting an analogy between dynamics in optical superlattices and discrete linear optics, we employ the Clements scheme to systematically construct any global $N$-dimensional single-particle
unitary from tunneling and phase shifts in arrays of double wells. Tunneling is controlled globally, while local operations are achieved through site-resolved potential shifts. We numerically investigate the susceptibility of the scheme to intensity noise and addressing crosstalk. We identify key subroutines enabled by this
unitary construction, including the Discrete
Fourier Transform and the implementation of non-native
Hamiltonians. Extending the scheme to two dimensions enables all-to-all atomic rearrangement with a
circuit depth that scales sublinearly with the atom number, providing a high-density and highly scalable approach to atom rearrangement.
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All authors Alexander Roth, Liyang Qiu, Timon Hilker, Titus Franz, Philipp M. Preiss
Materials Science
Electronic and structural properties of V$_2$O$_5$ layered polymorphs
Sakthi Kasthurirengan and Hartwin Peelaers
V$_2$O$_5$ is a promising battery electrode material that can intercalate not only Li, but also more abundant alkaline metals such as Na and K, and even multivalent ions such as Al, Ca, Cu, Mg, and Zn. V$_2$O$_5$ exhibits several different polymorphs, and phase transitions between the polymorphs can occur depending on intercalant or external conditions. At least 8 different layered polymorphs have been observed. However, detailed information about the energetics and structural properties of each polymorph is still lacking. To obtain a reliable computational reference, we use hybrid density functional theory calculations to investigate the properties of layered V$_2$O$_5$ polymorphs. We benchmarked several methods to include van der Waals interactions in combination with hybrid functionals, and found that the Grimme D3 method is most accurate. We obtain detailed information on the electronic properties and structures of the various unintercalated polymorphs and show that the main electronic effect of intercalants is a filling of the lowest conduction bands, as the intercalant contributions are well above the conduction-band minimum. Despite the structural differences between the unintercalated polymorphs, we find that they have very similar band gaps and band structures, with the exception of the high temperature and pressure phase $\beta$.
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