Mesoscale and Nanoscale Physics
Binayyak B. Roy, William B. Cason, Nimish Sharma et al. (+1 more)
We review the Pfaffian-based $\mathbb{Z}_2$ topological invariants in one dimensional
semiconductor-
superconductor (SM-SC) nanowire
heterostructures and clarify their validity in finite and disordered systems. For the clean nanowire, the product of the Pfaffians of the
Hamiltonian at particle-hole symmetric momenta $k=0,\pi$ changes sign at the topological phase transition defined by the bulk gap closing, leading to the definition of $\mathbb{Z}_2$ Kitaev invariant also known as Majorana number. We show that this momentum-space invariant is equivalent to a real space construction based on twisted boundary conditions, in which the sign of the product of the Pfaffians of the
Hamiltonian under periodic and anti-periodic boundary conditions defines the $\mathbb{Z}_2$ index. By introducing a superlattice description of periodically repeated disorder, we demonstrate that the real space Pfaffian invariant defined as the sign of the Pfaffians of the
Hamiltonian with periodic and anti-periodic boundary conditions, remains a well defined invariant even in the absence of microscopic translational
symmetry. Within this framework, it is also equivalent to the recently defined periodic disorder invariant (PDI), which constitutes an integer valued ($\mathbb{Z}$) topological invariant in the presence of
chiral symmetry. Finally, we prove that the sign of the Pfaffian of a quadratic
Hamiltonian equals the
fermion parity of its ground state, establishing a direct physical interpretation of the invariant, in terms of sign of the product of the ground state
fermion parity with periodic and anti-periodic boundary conditions. Numerical results confirm the correspondence between sign of the Pfaffian reversals, flux-induced level crossings, and ground-state parity switching in clean and disordered nanowires.
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All authors Binayyak B. Roy, William B. Cason, Nimish Sharma, Sumanta Tewari
Strongly Correlated Electrons
Thermal Hall conductivity from semiclassical spin dynamics simulations: implementation and applications to chiral ferromagnets and Kitaev magnets
Ignacio Salgado-Linares, Alexander Mook, Léo Mangeolle et al. (+1 more)
We investigate thermal
Hall transport in
magnetic systems, using semiclassical
spin dynamics simulations. Building on a linear response framework, we discuss the intricacies of computing the thermal
Hall conductivity from real-time energy current correlations and the energy magnetization. We then apply this methodology to two models: a square-
lattice chiral magnet with in-plane Dzyaloshinskii-Moriya interaction, and the
antiferromagnetic Kitaev model in a field. Our results demonstrate the efficiency of semiclassical
spin dynamics to study thermal
Hall transport capturing quantitative effects beyond the simple intrinsic non-interacting approximation. They can serve as a
benchmark for comparison with experiments in regimes where non-linearities from
magnon-
magnon interactions and strong thermal fluctuations play a crucial role.
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All authors Ignacio Salgado-Linares, Alexander Mook, Léo Mangeolle, Johannes Knolle
Strongly Correlated Electrons · Cross-listed from quant-ph
Coupled-Layer Construction of Quantum Product Codes
Shuyu Zhang, Tzu-Chieh Wei and Nathanan Tantivasadakarn
Product codes are a class of
quantum error correcting codes built from two or more constituent codes. They have recently gained prominence for a breakthrough yielding
quantum low-density parity-check (qLDPC) codes with favorable scaling of both code distance and encoding rate. However, despite its powerful algebraic formulation, the physical mechanism for assembling a general product code from its constituents remains unclear. In this letter, we show that the tensor and balanced product codes admit an intuitive coupled-layer construction by taking a stack of one code and condensing a set of excitations in the pattern given by the checks of the other code. We also make a connection to concatenated codes by showing that the tensor product code can be obtained by gauging large-weight logicals in concatenated codes, making them qLDPC. Our framework accommodates both classical or
quantum CSS input codes, unifies known physical mechanisms for constructing higher dimensional topological phases via anyon condensation, and naturally extends to non-topological codes.
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Strongly Correlated Electrons
Thermal and quantum fluctuations in extended Kitaev-Yao-Lee spin-orbital model
Jiefu Cen and Hae-Young Kee
Building upon the
spin-1/2 Kitaev model on a honeycomb
lattice, the Yao-Lee
spin-orbital model provides exactly solvable
quantum spin liquids with potentially better stability against perturbations due to the additional degree of freedom. Recently, the microscopic mechanism underlying the Yao-Lee interaction in honeycomb materials has been uncovered, leading to an extended Kitaev-Yao-Lee
spin-orbital model when the celebrated Kugel-Khomskii interaction is included. Numerical studies of this model have identified various disordered phases, including a broad region of the nematic phase that is reminiscent of a
spin-orbital
liquid. Here, we investigate the origin and stability of this nematic phase via thermal and
quantum fluctuations using classical Monte Carlo simulations and a generalized
spin wave theory appropriate for the
spin-orbital model. We demonstrate that the additional
spin-orbital degree of freedom gives rise to strong thermal and
quantum fluctuations in
spin-orbital models, providing insight into the emergence of disordered phases.
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Quantum Gases
Fermi-pressure-assisted superradiant transition with a mesoscopic Fermi gas in a cavity
Francesca Orsi, Ekaterina Fedotova, Rohit Prasad Bhatt et al. (+3 more)
We study the superradiant phase transition of a mesoscopic
Fermi gas comprising between a few tens and a few thousand $^6$Li atoms in a high-finesse cavity across a wide range of densities. We observe a non-monotonic variation of the superradiant threshold as a function of density, with a minimum reached when the
Fermi and
recoil wavevectors are comparable. The minimum corresponds to a crossover between
Fermi pressure-assisted ordering and Pauli blocking of
photon scattering, in good agreement with theory. This interpretation is confirmed by a study of the atom-number dependence of the ordering threshold and
photon number scaling. Our system opens the perspective of studying few-
fermion systems with strong and coherent light-matter coupling.
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All authors Francesca Orsi, Ekaterina Fedotova, Rohit Prasad Bhatt, Mae Eichenberger, Léa Dubois, Jean-Philippe Brantut
Statistical Mechanics
The quantum square-well fluid: a thermodynamic geometric view
J. L. López-Picón, L. F. Escamilla-Herrera, Alejandro Gil-Villegas et al. (+1 more)
We investigate several aspects of the thermodynamic geometry for a
quantum fluid with square-well interactions using a third-order perturbation theory framework based on the path-integral-necklace analogy. A comparison is made between the thermodynamic and
geometric properties of the
quantum fluid and its classical counterpart for the interaction ranges $\lambda ^{*}= 1.3$, 1.5, and 1.7. In particular, we analyze the scalar
curvature behavior, criticality, and the corresponding Widom lines derived from
curvature and several thermodynamic response functions.
Quantum effects are shown to smooth supercritical anomalies of the scalar
curvature and to shift its extrema for short-range interactions, while leaving the critical exponents of both the
curvature and its heat capacity consistent with mean-field predictions. Widom lines associated with temperature-dependent response functions and with the
curvature scalar exhibit pronounced classical-
quantum differences for short interaction ranges; in contrast, those derived from the isothermal compressibility exhibit only minor variations. Overall, these results highlight the sensitivity of
geometric information of thermodynamic systems due to
quantum effects and the crucial role of the interaction range in shaping supercritical thermodynamic behavior.
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All authors J. L. López-Picón, L. F. Escamilla-Herrera, Alejandro Gil-Villegas, José Torres-Arenas
Mesoscale and Nanoscale Physics
Nonlinear Mode Coupling in Silicon Nitride Membrane Resonators
Soumya Kanti Das, Nishta Arora, Hridhay A S et al. (+2 more)
Nonlinear interactions between vibrational modes play a crucial role in understanding the dynamical response of nanomechanical resonators. Here, we report the experimental observation and theoretical modeling of nonlinear mode coupling in a high-stress square silicon nitride membrane resonator. We quantify frequency shifts of the fundamental mode arising from tension-mediated
geometric nonlinearity by increasing the amplitude of the fundamental mode and higher-order flexural modes. A quantitative theoretical framework based on Kirchhoff-Love plate theory is developed, which incorporates both intrinsic Duffing nonlinearity and nonlinear intermodal coupling and shows good agreement with experimental measurements for the (1,1)-(2,1) and (1,1)-(2,2) mode pairs. We further compute the nonlinear coupling
matrix across mode families, revealing the role of mode
symmetry and spatial overlap in governing intermodal interactions. These results establish nonlinear mode coupling as a controllable resource for multimode frequency tuning and mechanical transduction.
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All authors Soumya Kanti Das, Nishta Arora, Hridhay A S, Akshay Naik, Chandan Samanta
Superconductivity
Evidence of intertwined pair density and charge density wave orders in UTe2
Zhen Zhu, Yudi Huang, Julian May-Mann et al. (+9 more)
The strongly correlated
spin-triplet
superconductor UTe2 hosts an unusual landscape of
magnetic-field-sensitive charge density wave (CDW) phases, positioning it as a compelling system for studying intertwined electronic orders. A central challenge is determining whether the observed charge modulations arise from a triplet pair density wave (PDW) order and, if so, how the anisotropic
magnetic field response of triplet superconductivity is manifested in the CDW response. Here, using a scanning tunneling microscope equipped with a vector
magnetic field, we systematically investigate the
evolution and interrelation of distinct CDW orders. Complementing the previously identified incommensurate CDW peaks (qi=1,2,3), we resolve an additional set of nondispersive modulations (pi=1,2,3 and h1,2) with distinct temperature and
magnetic field dependencies. The pi CDW peaks vanish near Tc, while the qi peaks survive well above Tc but are progressively suppressed by
magnetic field in an anisotropic manner. The critical fields of the qi peaks mirror the directional hierarchy of Hc2, which suggests a PDW is present above the bulk Tc. This is consistent with a Landau free-energy picture where PDWs with wavevectors pi form above the bulk Tc, leading to composite CDW orders with wavevector qi. Below Tc, the coupling of PDWs and uniform superconductivity leads to the pi CDWs. Together, these findings establish UTe2 as a rare platform where both the parent PDW and descendant orders are directly resolved, enabling access to both the fundamental and emergent manifestations of PDW physics.
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All authors Zhen Zhu, Yudi Huang, Julian May-Mann, Kaiming Liu, Zheyu Wu, Shanta R. Saha, Johnpierre Paglione, Alexander G. Eaton, Andrej Cabala, Michal Vališka, Eduardo Fradkin, Vidya Madhavan
Statistical Mechanics · Cross-listed from physics.optics
Experimental investigation of Lévy flights for step-length distributions with a length-dependent local power exponent
Isaac C. Nunes, Jesús P. López and Thierry Passerat de Silans
We experimentally investigate the transmission of light by dense atomic vapor. The light propagating in dense atomic vapor can be modeled as a Lévy flight random walk. For such system, the step-length distribution can be modeled as $P(\ell)\sim \ell^{-1-\alpha(\ell)}$, with the Lévy index $\alpha(\ell)$ varying smoothly with the step length. Moreover, the walkers alternate between two distinct distributions depending on the occurrence of collisions between atoms in the light scattering. We obtain the Lévy index from transmission measurements for different system sizes and atomic densities. The measured Lévy index is determined by the system size $\alpha=\alpha(\ell=L)$. Simulations are made for walkers alternating between two Lévy like step-length
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Strongly Correlated Electrons
Revisiting the $J_1$-$J_2$ Heisenberg Model on a Triangular Lattice: Quasidegenerate Ground States and Phase Competition
Oleksandra Kovalska, Ester Pagès Fontanella, Benedikt Schneider et al. (+2 more)
It is generally believed that the
spin-$\tfrac{1}{2}$ triangular-
lattice $J_1$-$J_2$ Heisenberg model hosts a
quantum spin liquid in the intermediate regime between the $120^\circ$ and stripe ordered phases. Density
matrix renormalization group studies on cylinders have consistently found two nearly degenerate ground states, commonly interpreted as distinct topological sectors. Using state-of-the-art
matrix product state simulations on YC6 cylinders, we compare the static and dynamical properties of these two sectors at $J_2/J_1 = 0.125$. Noticeable differences appear already in static correlations; moreover, high-resolution dynamical structure factors reveal qualitatively distinct low-energy excitations. These results suggest that the two ground states cannot be understood as merely topologically distinct sectors of a gapped $\mathbb{Z}_2$
spin liquid.
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All authors Oleksandra Kovalska, Ester Pagès Fontanella, Benedikt Schneider, Hong-Hao Tu, Jan von Delft
Soft Condensed Matter
Fluid-Solid Pattern Formation and Strain Localisation via Shear Banding Instability in Model Biological Tissues
Aidan J. Nicholas and Suzanne M. Fielding
The rheological properties of biological tissues are core to processes such as cancer metastasis, wound healing and embryo development. The emergence of tissue and organ structures during morphogenesis requires the precise formation of spatial patterns. Dating back to Turing, pattern formation has been suggested to arise in tissues via spontaneous
symmetry breaking instabilities in the concentration field of chemical morphogens. Within the vertex model of tissue mechanics, we show that spontaneous
symmetry breaking may also arise via a mechanical instability in the strain field of a deformed tissue, leading to a patterned coexistence of fluid and solid regions, with a strong localisation of the strain into shear bands. The nature of the bands differs between tissues in which internal
cell-
cell dissipation dominates external drag against a substrate, and vice versa.
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Statistical Mechanics · Cross-listed from quant-ph
The Grasshopper Problem on the Sphere
David Llamas, Dmitry Chistikov, Adrian Kent et al. (+2 more)
The spherical grasshopper problem is a
geometric optimization problem that arises in the context of Bell inequalities and can be interpreted as identifying the best local hidden variable approximation to
quantum singlet correlations for measurements along random axes separated by a fixed angle. In a parallel publication [arXiv:2504.20953], we presented numerical solutions for this problem and explained their significance for singlet simulation and testing. In this companion paper, we describe in detail the
geometric and computational framework underlying these results. We examine the role of spherical discretization and compare three natural variants of the problem: antipodal complementary lawns, antipodal independent lawns, and non-antipodal complementary lawns. We analyze the
geometric structure of the corresponding optimal lawn configurations and interpret it in terms of a spherical harmonics expansion. We also discuss connections to other physical models and to classical problems in
geometric probability.
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All authors David Llamas, Dmitry Chistikov, Adrian Kent, Mike Paterson, Olga Goulko
Mesoscale and Nanoscale Physics
Microwave response of electrically driven spins in a three-qubit quantum processor
Tanner M. Janda, Heun Mo Yoo, Connor Nasseraddin et al. (+3 more)
In electric dipole
spin resonance (EDSR), a single
spin is electrically driven in the field gradient produced by a micromagnet. While EDSR has enabled high fidelity gate operations in many devices, there are reports of unexpected non-linearities in the Rabi frequency as a function of microwave drive amplitude. We carefully measure the response of Loss-DiVincenzo (LD) single
spin qubits to resonant drives as well as simultaneous resonant and off-resonant drives, as would be encountered in a realistic
quantum processor. With the microwave amplitude carefully calibrated, we find that the Rabi frequency scales linearly with drive amplitude, even when all three
spins are driven simultaneously. We also determine that heating-induced resonance frequency shifts from off-resonant drives are comparable to typical temporal drifts. Our results indicate that the previously observed nonlinear response is not a general feature of LD
spin qubits.
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All authors Tanner M. Janda, Heun Mo Yoo, Connor Nasseraddin, Adam R. Mills, Zhaoyi Joy Zheng, Jason R. Petta
Materials Science
A Kagome-Derived Mosaic Lattice Family A3V9Te13 (A = Cs, Rb) with Tunable Strong Electronic Correlations
Yusen Xiao, Zhibin Qiu, Qingchen Duan et al. (+5 more)
The pursuit of geometrically frustrated
lattices beyond conventional paradigms remains a central challenge in the design of
quantum materials. Herein, we report the discovery of the A3V9Te13 (A = Cs, Rb) family of vanadium-based intermetallic compounds, which host a unique two-dimensional Mosaic
lattice derived from the Kagome network, composed of an ordered tessellation of triangles, squares, and pentagons. The Cs compound (CVT) exhibits strong electronic correlations, characterized by non-
Fermi liquid behavior at low temperatures, an exceptionally large Sommerfeld coefficient, and a bulk phase transition at T* $\approx$ 47 K with possible charge- or
spin-related origin. Inspired by pressure-tuning in related Kagome systems, we demonstrate that the electronic ground state of this
lattice is exquisitely tunable via chemical pressure. Systematic substitution of Cs with smaller Rb ions suppresses the T* phase transition and the correlated electronic response, ultimately driving the system into a highly frustrated semiconducting ground state without long-range
magnetic order down to 60 mK. This work unveils a new structural platform for exploring the interplay between
geometric frustration and strong electron correlations, providing a chemically controllable platform for exploring the phase space between distinct correlated electronic states.
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All authors Yusen Xiao, Zhibin Qiu, Qingchen Duan, Zhaoyi Li, Xiaotong Xu, Hengxin Tan, Shu Guo, Ruidan Zhong
Materials Science
Au and Ag nanoparticles produced by ion implantation in single-crystalline $\beta$-Ga$_2$O$_3$
Duarte Magalhães Esteves, Ana Sofia Sousa, Inês Freitas et al. (+5 more)
This work reports the successful formation of Ag and Au nanoparticles in $\beta$-Ga$_2$O$_3$ single-
crystals by ion implantation and annealing at 550 {\deg}C. X-ray diffraction measurements revealed that nanoparticles were formed after the annealing step, presenting a highly-ordered crystalline structure and conforming to a crystallographic relation with respect to the
matrix: $\left(0\overline{1}0\right)_\beta \parallel \left(110\right)_{\mathrm{Ag/Au}}$ and $\left[102\right]_\beta \parallel \left[1\overline{1}2\right]_{\mathrm{Ag/Au}}$. The presence of these nanoparticles was also confirmed via absorbance measurements revealing the localised surface plasmon resonance peaks associated with these particles. Considering the multiple advantages and the versatility of metallic nanoparticles, their combination with the exceptional properties of $\beta$-Ga$_2$O$_3$ paves the way for a wide range of applications.
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All authors Duarte Magalhães Esteves, Ana Sofia Sousa, Inês Freitas, Ângelo Rafael Granadeiro da Costa, Joana Madureira, Sandra Cabo Verde, Katharina Lorenz, Marco Peres
Materials Science
Anisotropic implantation damage build-up and crystal recovery in $\beta$-Ga$_2$O$_3$
Duarte Magalhães Esteves, Sérgio Magalhães, Ângelo Rafael Granadeiro da Costa et al. (+2 more)
The present work aims at investigating the defect accumulation and recovery dynamics in the inherently anisotropic $\beta$-Ga$_2$O$_3$
lattice. A systematic Rutherford Backscattering Spectrometry in Channelling mode (RBS/C) analysis of Cr-implanted samples was performed across multiple surface orientations and channelling directions. Distinct apparent defect accumulation and annealing rates were observed along different channelling axes, mainly attributed to the shadowing of certain types of defects along some directions. The efficient defect removal observed after annealing was correlated with the strain relaxation observed via High-Resolution X-ray diffraction (HRXRD) at temperatures as low as 500 {\deg}C, which is attributed to the removal of point defects. Annealing at higher temperature further improves crystalline quality but at a slower rate. In short, this work enhances the understanding of the effect of structural anisotropic properties of $\beta$-Ga$_2$O$_3$ during ion implantation, as well as the
crystal recovery during thermal annealing, highlighting the interplay between crystallography and defect dynamics.
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All authors Duarte Magalhães Esteves, Sérgio Magalhães, Ângelo Rafael Granadeiro da Costa, Katharina Lorenz, Marco Peres
Strongly Correlated Electrons
Collinear spin density wave state in distorted square-lattice GdNiSn$_4$
Charles C. Tam, Sarah Schwarz, Xin Zhang et al. (+5 more)
We characterize the
magnetic ground state of the newly synthesized lanthanide intermetallic GdNiSn$_4$ via resonant elastic x-ray scattering measurements. This compound forms distorted square nets of Gd that initially order magnetically below 23 K followed by a lower temperature transition at 16 K. Our scattering data identify the ground state order as a single-$q$ incommensurate, collinear order that slides towards a commensurate wave vector above the 16 K transition.
Magnetic symmetry analysis combined with azimuthal dependence resolves the ground state
magnetic structure as a moment-modulated
spin density wave state with Gd moments oriented parallel to the in-plane a-axis. We discuss connections between the observed
magnetic order and electronic properties in this square-net compound.
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All authors Charles C. Tam, Sarah Schwarz, Xin Zhang, Sudipta Chatterjee, Scott B. Lee, Rebecca Scatena, Leslie M. Schoop, Stephen D. Wilson
Materials Science
Defect-induced multiferroicity in bulk solid solutions of WSe$_2$ and WTe$_2$
H. Rojas-Páez, G. Villabón-Linares, J. Pazos et al. (+5 more)
Transition metal dichalcogenides provide a versatile platform for tunable ferroic phenomena at the atomic scale owing to their reduced dimensionality. Here we investigate the structural,
magnetic, and ferroelectric properties of bulk solid solution W(Se1-xTex)2(1-delta) single
crystals synthesized by chemical vapor transport. The room temperature behavior is analyzed as a function of tellurium concentration (x) and chalcogen defect fraction (delta). X ray diffraction and Raman spectroscopy reveal
lattice expansion and
symmetry reduction with increasing x, consistent with a 2H to 1Td structural transition above a critical composition xc about 18 percent. Piezoresponse force microscopy identifies piezoelectricity near stoichiometric compositions (delta less than 5 percent) and switchable ferroelectricity in the chalcogen deficient regime (delta greater than 20 percent). Magnetometry measurements show a corresponding
evolution from paramagnetic to
ferromagnetic behavior with increasing delta. Near stoichiometric Te poor samples exhibit piezoelectric and paramagnetic responses, whereas multiferroic states characterized by the coexistence of ferroelectric and
ferromagnetic responses emerge at high vacancy concentrations. The performed characterizations indicate that x primarily governs structural
symmetry, while delta controls the emergence of both
ferromagnetic and ferroelectric responses. These trends are summarized in a configurational phase diagram highlighting the cooperative influence of dopants and defects on ferroic behavior. Overall, controlled stoichiometry and vacancy engineering offer an effective strategy to tailor ferroic responses in transition metal dichalcogenides.
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All authors H. Rojas-Páez, G. Villabón-Linares, J. Pazos, E. Ramos, R. Moreno, O. Herrera-Sandoval, J. A. Galvis, P. Giraldo-Gallo
Superconductivity
Magnetic landscape of NbTiN superconducting resonators under radio-frequency excitation
J. Baumgarten, N. Lejeune, L. Nulens et al. (+3 more)
Planar superconducting resonators are essential components in
quantum circuits and highly sensitive sensors. However, their performance is often compromised by
magnetic flux penetration, as the interaction of flux quanta and the induced
radio-frequency (RF) currents in the superconducting thin film leads to significant energy dissipation. At low operating temperatures, this issue is aggravated as thermomagnetic instabilities can trigger the sudden propagation of
magnetic flux avalanches. An important open question is whether the RF excitation itself stimulates the nucleation and propagation of
magnetic flux avalanches in the superconducting thin film. The literature remains inconclusive on this point, partly due to the lack of compelling evidence for this phenomenon. In this work, we address this issue by unprecedented direct visualization of
magnetic flux penetration through Faraday rotation imaging under simultaneous RF excitation. We demonstrate that the avalanche activity exhibits a weak dependence on the RF intensity for RF excitations within the linear Campbell regime. However,
magnetic flux bursts clearly influence the RF transmission properties of the device. Furthermore, it is possible to unambiguously associate a particular avalanche event with a jump in resonance frequency. This enables us to identify the loci of most deleterious events and understand the distinct origins of upward and downward frequency shifts. These observations are supported by electromagnetic simulations in which local changes of the kinetic inductance mimic flux avalanches and confirm the invasive character of the MOI technique. The insights gained from this study aim to contribute to the broader understanding of the
magnetic resilience of superconducting resonators, with the goal of improving their efficiency and stability.
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All authors J. Baumgarten, N. Lejeune, L. Nulens, I. P. C. Cools, J. Van de Vondel, A. V. Silhanek
Soft Condensed Matter
Modeling the Slow Arrhenius Process (SAP) in Polymers
Valeriy V. Ginzburg, Oleg V. Gendelman, Simone Napolitano et al. (+2 more)
Amorphous glass-forming
polymers exhibit multiple relaxation processes, including the structural {\alpha}-relaxation associated with the glass transition and faster secondary relaxations that typically follow Arrhenius behavior. Recently, a distinct slow Arrhenius process (SAP) has been observed at frequencies well below the {\alpha}-process. Although Arrhenian in its temperature dependence, the SAP involves much longer relaxation times and its microscopic origin remains unclear. Here, we extend the two-state, two-timescale (TS2) theory to describe both the {\alpha}-relaxation and the SAP within a unified framework. We propose that the SAP represents the high-temperature limit of an {\alpha}-like process in a coarse-grained fluid of dynamically correlated clusters. With renormalized interaction energies and coordination parameters, the same model quantitatively reproduces both {\alpha} and SAP data across multiple
polymers without additional adjustable parameters and explains the observed Meyer-Neldel compensation behavior. The theory further predicts that the SAP should deviate from Arrhenius behavior at sufficiently low temperatures, transitioning to Vogel-Fulcher-Tammann-Hesse-like dynamics, thereby offering a physically transparent interpretation of cluster-scale relaxation in glass-forming
polymers.
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All authors Valeriy V. Ginzburg, Oleg V. Gendelman, Simone Napolitano, Riccardo Casalini, Alessio Zaccone
Mesoscale and Nanoscale Physics
Non-local effects in charge and energy transport with dissipative electrodes
Rodolfo A. Jalabert
Recent advances in nano-thermometry motivate the extension of the Landauer-Büttiker scattering theory as to include the non-local dissipation associated with charge transport. Such a program is implemented by describing the inelastic scattering in the connecting electrodes within an electrostatically self-consistent scheme. The restriction to quasi-one-dimensional geometries, weak excitation and low temperature allows to obtain general expressions of the current density and the dissipated power, valid in different regimes, for the cases of an energy-independent mean-free-path or an energy-independent relaxation-rate. In particular, the dissipation asymmetry at both sides of a nano-device and the conditions for observing heating spots with a local maximum of the dissipated power are formulated in terms of the key parameters that define the nano-device and its environment.
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Materials Science
Second harmonic study of thermally oxidized mono- and few-layer 2H-MoS2
Katharina Burgholzer, Henry Volker Hübschmann, Gerhard Berth et al. (+5 more)
A comprehensive study of second harmonic generation on thermally oxidized MoS2 flakes with thickness ranging from monolayer up to seven layers is presented. Observing the fundamental nonlinear behavior for non-treated and oxidized MoS2 reveals that oxidation causes significant changes in the second harmonic (SH) response for all investigated structures. Excitation power dependent measurements to analyze the nonlinear behavior with respect to the oxidation time show progressive oxidation within the maximum oxidation time of six hours, under the considered oxidation conditions. Here, polarization dependent measurements reveal the structural changes due to oxidation. Additionally, it is found that the oxidation depth is restricted to the top most layer and the oxidation behavior exhibits a layer dependency. These findings are supported by theoretical band structure calculations. The results demonstrate that the thermal oxidation progress of two dimensional MoS2 can be monitored with non-resonant and non-invasive SH microscopy, by following distinct fingerprints of structural modification in the nonlinear response.
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All authors Katharina Burgholzer, Henry Volker Hübschmann, Gerhard Berth, Adriana Bocchini, Uwe Gerstmann, Wolf Gero Schmidt, Klaus D. Jöns, Alberta Bonanni
Strongly Correlated Electrons
Stochastic Loop Corrections to Belief Propagation for Tensor Network Contraction
Gi Beom Sim, Tae Hyeon Park, Kwang S. Kim et al. (+6 more)
Tensor network contraction is a fundamental computational challenge underlying
quantum many-body physics, statistical mechanics, and machine learning. Belief propagation (BP) provides an efficient approximate solution, but introduces systematic errors on graphs with loops. Here, we introduce a hybrid method that achieves accurate results by stochastically sampling loop corrections to BP and showcase our method by applying it to the two-dimensional
ferromagnetic Ising model. For any pairwise Markov random field with symmetric edge potentials, our approach exploits an exact factorization of the partition function into the BP contribution and a loop correction factor summing over all valid loop configurations, weighted by edge weights derived directly from the potentials. We sample this sum using Markov chain Monte Carlo with moves that preserve the loop constraint, combined with umbrella sampling to ensure efficient exploration across all correlation strengths. Our
stochastic approach provides unbiased estimates with controllable statistical error in any parameter regime.
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All authors Gi Beom Sim, Tae Hyeon Park, Kwang S. Kim, Yanmei Zang, Xiaorong Zou, Hye Jung Kim, D. ChangMo Yang, Soohaeng Yoo Willow, Chang Woo Myung
Soft Condensed Matter
Torque Hyperuniformity in Frictional Granular Matter - Theory and Experiments
Jin Shang, Jie Zhang and Itamar Procaccia
A question of some fundamental importance is whether a given assembly of frictional granules (say sand or powder) will exhibit stress autocorrelations with long-range anisotropic decay as determined by the elastic Green's function. In
Hamiltonian systems with central forces, mechanical balance and material isotropy demand the stress auto-correlation
matrix to be fully determined by the pressure auto-correlation only. If the local pressure fluctuations are normal, it follows that stress autocorrelations decay at long distance like the elastic Green's function. With friction,
Hamiltonian symmetry is lost, and one may expect more constraints. Indeed, it was shown recently that for frictional amorphous solids mechanical balance and material isotropy demand the stress auto-correlation
matrix to be fully determined by two spatially isotropic functions: the pressure and torque auto-correlations. Elastic-like decay of the stress autocorrelations follows from normal fluctuations of the pressure and from the torque fluctuations being hyperuniform. The theoretical discovery of these conditions required experimental confirmation, to test whether these conditions are generically obeyed in actual frictional amorphous solids. Recently the confirmation was announced for 2-dimensional amorphous assemblies of frictional disks under isotropic load, in which torque is caused by tangential forces only. In this paper we review that case and report confirmation of the theoretical predictions in 2-dimensional systems of disks under shear and in isotropically loaded frictional ellipses, where contributions to torque come also from normal forces. The paper ends with physical explanations of the hyperuniformity of the torque fluctuations and predictions for how the results are expected to extend to d-dimensions.
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Mesoscale and Nanoscale Physics
Optical manipulation of valley coherence via Landau level transitions in black phosphorus and WTe2 monolayers
Xinyu Mu, Shihao Li, Xiaoying Zhou et al. (+1 more)
Valley coherence is of great significance for exploring fundamental
quantum phenomena and developing next-generation valleytronic devices. Herein, we theoretically investigate the valley
quantum interference engineered by inter-Landau level (LL) transitions in black phosphorus (BP) and WTe2 monolayers. In contrast to the non-Landau-quantized regime, valley
quantum interference is enhanced by over 20-fold, or even significantly stronger, in virtue of striking anisotropic environment. Such anisotropy originates from the distinct electron transition probabilities along the armchair and zigzag directions of BP and WTe2 monolayers. Especially, BP is capable of more effectively strengthening the valley
quantum interference response due to its greater directional disparity in electron transition probabilities. The interference fringes also present distinct spectral profiles (e.g., different dip and peak numbers in one interference period) owing to different transition selection rules in BP and WTe2 monolayers. In spite of these discrepancies, normalized interference intensities follow two exponential functions of
magnetic field and Landau level index for all the transitions {\delta}n = n'- n = -4, -2, 0, +2, +4 (where n and n' indicate the LL indexes of valence and conduction bands, respectively), and the interference spectra exhibit C2 rotational
symmetry about the crystallographic azimuthal angle of 90{\deg}.
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All authors Xinyu Mu, Shihao Li, Xiaoying Zhou, Guangyi Jia
Strongly Correlated Electrons
Microscopic theory of flexo Dzyaloshinskii-Moriya-type interaction
Takehito Yokoyama
We study interaction between two
magnetic impurities mediated by itinerant electrons on the surface of curved magnets based on perturbation theory. We show that Dzyaloshinskii-Moriya type interaction can arise from inhomogeneous
spin texture by bending, without any
spin-orbit coupling. Analytical expressions of the Dzyaloshinskii-Moriya type interaction are obtained. We demonstrate this effect in a one-dimensional ring model.
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Materials Science
Unveiling the Thermal and Aqueous Stability of 1D Lepidocrocite Titania
Risha A. Iythichanda, Sukanya Maity, Mustafa M. Aboulsaad et al. (+3 more)
One dimensional lepidocrocite titanium dioxide filaments are investigated with respect to their thermal and aqueous stability. Structural and phase
evolution are examined using in situ heating in
vacuum within transmission electron microscopy combined with electron energy loss spectroscopy, and at ambient conditions using Raman spectroscopy. The filaments retain their lepidocrocite structure up to 300 degree and above which localized sintering and amorphization occur at filament overlap junctions. With further heating, the amorphous regions crystallize into anatase, with Raman spectroscopy corroborating the onset of structural disorder. Long term aqueous storage up to 100 days at ambient conditions induces transformation into flake like anatase nanoparticles. This process is strongly suppressed under refrigerated storage, where no structural changes are observed over the same period. These results establish critical thermal and environmental stability thresholds that define operational advantages and limits for emerging applications of 1D lepidocrocite filaments.
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All authors Risha A. Iythichanda, Sukanya Maity, Mustafa M. Aboulsaad, Tomas Edvinsson, Johanna Rosen, Per O.Å. Persson
Statistical Mechanics
Synchronization of higher-dimensional Kuramoto oscillators on networks: from scalar to matrix-weighted couplings
Anna Gallo, Renaud Lambiotte and Timoteo Carletti
The Kuramoto model is the paradigmatic model to study synchronization in coupled oscillator systems. In its classical formulation, the oscillators move on the unit circle, each characterized by a scalar phase and a natural frequency, by interacting through a sinusoidal coupling. In this work, we propose a d-dimensional generalization in which oscillators are represented as unit vectors on the (d-1)-sphere and interact through a
matrix-weighted network (MWN), a recently introduced framework where links are endowed with a
matrix weight instead of a scalar one. We derive necessary conditions for global synchronization via a Master Stability Function approach: the existence of a synchronous solution requires identical frequency
matrices across nodes and, in the MWN case, a coherence condition on the network structure. Through a suitable change of variables, the stability analysis reduces the full Nd-dimensional problem to a family of d-dimensional
eigenvalue problems, each one parametrized by the
eigenvalue of a suitable scalar weighted
Laplacian, showing that the synchronous solution is locally stable for any positive coupling strength K on any connected network. Analytical results are complemented by numerical simulations.
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Mesoscale and Nanoscale Physics
Bound Trions in Two-Dimensional Monolayers: A Review
Roman Ya. Kezerashvili
Trions – Coulomb-bound three-particle excitations composed of two like-charge carriers and one oppositely charged carrier – are central quasiparticles in two-dimensional
semiconductors. Reduced dielectric screening and
quantum confinement strongly enhance their binding energies, making them robust and experimentally accessible. This review surveys theoretical and experimental advances in trion physics, emphasizing rigorous few-body approaches and the role of dielectric environment, anisotropy, and external electric and
magnetic fields. We analyze computational methods for describing trions in two-dimensional configuration spaces and discuss how reduced dimensionality modifies their structure and stability. Connections to many-body phenomena, including screening, Landau-level mixing, and
exciton–polaron crossover, are also highlighted.
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Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Mathematical modeling of urban sprawl
Marc Barthelemy and Ulysse Marquis
Urban land cover doubled between 1985 and 2015, yet the spatial dynamics of urban form remain under-quantified, despite its importance for sustainability, infrastructure planning, and
climate risk. Urban expansion is a non-
equilibrium process shaped by interactions between population growth, infrastructure, institutions, and
market failures – rendering static and
equilibrium models inadequate. We review key challenges and modeling approaches, focusing on partial differential equation (PDE) frameworks. Borrowed from statistical physics, PDEs capture spatial heterogeneity, anisotropy, stochasticity, and feedbacks between land use and transport networks. Integrating economic and institutional factors remains a major challenge for policy relevance. We propose a research agenda that bridges remote sensing, urban economics, and complexity science to develop dynamic, empirically grounded models of urban expansion.
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