Statistical Mechanics
Turing patterns in Matrix-Weighted Networks
Anna Gallo, Wilfried Segnou and Timoteo Carletti
Diffusion-driven instability is a fundamental mechanism underlying pattern formation in spatially extended systems. In almost all existing works,
diffusion across the links of the underlying network is modeled through scalar weights, possibly complemented by cross-
diffusion terms that are homogeneous across links. In this work, we investigate the emergence of Turing patterns on
Matrix Weighted Networks (MWNs), a recently introduced framework in which each edge is associated with a
matrix weight. Focusing on the class of coherent MWNs, we provide a novel characterization of coherence in terms of node-dependent orthonormal
matrices, showing that link transformations can be written as relative rotations between nodes. This representation allows us to deal with coherent MWNs of any size and to introduce an orthonormal change of variables capable to reduce
diffusion on a coherent MWN to
diffusion on a standard weighted network with scalar weights. Building on this, we extend the classical Turing instability analysis to MWNs and derive the conditions under which a homogeneous
equilibrium of the local dynamics loses stability due to
matrix-weighted
diffusion. Moving beyond the dimensional constraints of previous approaches, our results show how network
topology, scalar weights, and inter-node transformations jointly shape pattern formation, and provide a constructive framework to analyze and design Turing patterns on
matrix-weighted and higher-order networked systems.
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Statistical Mechanics
Topological Reorganization and Coordination-Controlled Crossover in Synchronization Onset on Regular Lattices
Gunn Kim
The transition to global synchronization in coupled dynamical systems is governed by the interplay between coupling strength and structural
topology. Although abrupt, first-order-like synchronization transitions have been extensively reported in heterogeneous networks, it is unclear whether comparable accelerated onset behavior can emerge purely from coordination geometry in spatially homogeneous, regular
lattices. In this study, we investigate large-scale ($N=10^5$)
stochastic Stuart-Landau oscillator networks defined on regular
lattices with controlled coordination number. Using topological data analysis (TDA), simplicial-complex characterization, and optimal-transport-based
geometric diagnostics, we identify a coordination-controlled crossover in synchronization onset dynamics at approximately $z_{c} \approx 7$ within the class of regular
lattices considered. Low-coordination
lattices ($z < z_{c}$) exhibit persistent $H_2$ topological features in the dynamical amplitude field that correlate with delayed coherence and surface-limited propagation. In contrast, higher-coordination
lattices ($z > z_{c}$) display rapid fragmentation of these features, reduced interface roughness, and predominantly positive
Ricci curvature. This is consistent with enhanced path redundancy and improved transport efficiency. In this regime, the global order parameter exhibits accelerated exponential-like growth during the onset stage. Throughout this work, abrupt synchronization refers specifically to this exponential onset behavior rather than to thermodynamic first-order hysteresis. Our results demonstrate that increasing coordination density induces a qualitative reorganization of higher-order topological structure that strongly correlates with synchronization efficiency in regular
lattice systems.
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Materials Science
Mystery of the 175 cm$^{-1}$ Raman Mode in MnTe Altermagnet
Bishal Thapa, K. D. Belashchenko and Igor I. Mazin
MnTe has recently attracted exceptional
attention due to its well-established altermagnetism, prompting a thorough reexamination of its properties. In particular, it was found that a Raman-active excitation at ~175 cm$^{-1}$, routinely assigned to the E2g
phonon, is incompatible with this interpretation. It was further hypothesized that this mode is a "leakage", due to
symmetry lowering, of an otherwise forbidden
phonon. Here, using first-principles calculations, we decisively rule out this hypothesis and propose an alternative interpretation that the "mystery mode" is an electronic excitation, i.e., a plasmon, enabled by hole self-doping. The resolution of this mystery will require additional experiments and shed new light on the nature of electronic transport in MnTe.
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Superconductivity
Quantitative imaging of Abrikosov vortices by scanning quantum magnetometry
Clemens Schäfermeier, Ankit Sharma, Christopher Kelvin von Grundherr et al. (+5 more)
Understanding
vortex matter in type-II
superconductors is central to controlling dissipation and flux pinning in superconducting materials and devices. Here, we use cryogenic scanning nitrogen vacancy magnetometry (NVM) to image Abrikosov
vortices in the cuprate
superconductors BSCCO-2212 and YBCO under controlled field-cooled conditions. Measurements, which are performed using continuous-wave optically detected
magnetic resonance (cw-ODMR) in a closed-cycle cryostat, yield quantitative
magnetic-field maps with nanoscale spatial resolution. In BSCCO-2212 at 71 K, we resolve a well-ordered triangular
vortex lattice, whose
symmetry and spacing are confirmed through 2D
Fourier analysis and are consistent with flux quantization. YBCO thin films imaged at 3 K exhibit a more disordered
vortex arrangement reflecting stronger pinning, while maintaining quantitative agreement between measured
vortex density and the applied
magnetic field. These results render our cryogenic scanning NVM a reliable quantitative tool for real-space studies of
vortices in high-$T_c$
superconductors, in particular since such a remarkable
magnetic resolution has been achieved within relatively short acquisition times of 2 to 4 h.
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All authors Clemens Schäfermeier, Ankit Sharma, Christopher Kelvin von Grundherr, Dieter Andres, Andrea Morales, Jan Rhensius, Gabriel Puebla-Hellmann, Mirko Bacani
Materials Science
Negative thermal expansion in ice I polytypes
Leonardo del Rosso, A. Dominic Fortes, Daniele Colognesi et al. (+4 more)
The fundamental properties of ice have always attracted a lot of interest due to omnipresence of ice in many different natural contexts. Since cubic ice recently become experimentally accessible from a low-density gas hydrate precursor [1, 2], it has been possible to measure its density as a function of temperature in the whole thermodynamic range of metastability. We found strong analogies with respect to the other ice I polytype, i.e., hexagonal ice Ih [3], including the presence of a negative thermal expansion behavior at low temperature. Based on these results, a new enthalpy calculation quantifies the metastable nature of the cubic form and, consequently its inaccessibility from a "normal" ice Ih precursor.
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All authors Leonardo del Rosso, A. Dominic Fortes, Daniele Colognesi, Alberto Santonocito, Francesco Grazzi, Selene Berni, Milva Celli
Strongly Correlated Electrons
Topology of the Fermi surface and universality of the metal-metal and metal-insulator transitions: $d$-dimensional Hatsugai-Kohmoto model as an example
Gennady Y. Chitov
The earlier theory [1] of the
quantum phase transitions related to the change of the
Fermi Surface
Topology (FST) is advanced. For such transitions the
Fermi surface as a
quantum critical
manifold determined by the Lee-Yang zeros, the order parameter $\mathcal{P}$ as the $d$-volume of the
Fermi sea, and the special FST universality class were introduced in [1]. The exactly solvable Hatsugai-Kohmoto (HK) $d$-dimensional ($d=1,2,3$) model of interacting
fermions is analyzed. We explore the relation between the Lee-Yang zeros, the Luttinger and the plateau (Oshikawa)
theorems. The validity of the Luttinger
theorem in the HK model is confirmed. It is shown that the order parameter $\mathcal{P}$ and the FST universality class describe the transitions between metal and band/Mott
insulators, as well as the Lifshitz and van Hove gapless-to-gapless transitions. The gapless phases are established to be the Landau
Fermi liquids (metals). In addition to the conventional paradigm with a continuous order parameter, we apply the homology theory to analyze the FST transitions. They are critical points of the Morse function. To quantify FST we use the Euler characteristic, which is calculated for each phase of the HK model. We claim that the FST universality class is robust with respect to interactions and other model details, under the condition that the critical points are non-degenerate.
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Soft Condensed Matter
Modulated Anti-Ferroelectric Smectic Phases with Orthogonal and Tilted Structures
Jordan Hobbs, Calum J. Gibb, William C. Ogle et al. (+5 more)
The discovery of the ferroelectric nematic phase has brought with it a plethora of new polar
liquid crystalline phases. One in particular is the anti-ferroelectric smectic A SmA\textsubscript{AF} phase. In this letter we show via observation and analysis of satellite peaks in the X-ray scattering pattern that the structure of the SmA\textsubscript{AF} phase involves a density modulation of $\approx$10-20 nm lateral to the smectic layer normal. Further, we demonstrate a previously undiscovered phase where the anti-ferroelectric order is maintained into a tilted smectic phase demonstrating the robustness of the underlying frustration that leads to the modulated structure. We suggest that the modulations are only in a single dimension and appear parallel to the tilt plane. This new phase also shows a significantly different and complex response to an electric field from other discovered polar LC phases due to the ability to modulate both tilt and polarisation direction.
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All authors Jordan Hobbs, Calum J. Gibb, William C. Ogle, Peter Medle Rupnik, Natan Osterman, Nerea Sebastián, Alenka Mertelj, Richard J. Mandle
Strongly Correlated Electrons
Variational study of the magnetization plateaus in the spin-1/2 kagome Heisenberg antiferromagnet: An approach from vision transformer neural quantum states
Andreas Raikos, Sylvain Capponi and Fabien Alet
We analyze the magnetization curve of the
spin-1/2 kagome Heisenberg model in a
magnetic field. Using state-of-the-art variational wave functions based on neural networks, we confirm the presence of robust magnetization plateaus at $m=1/3$, $5/9$ and $7/9$ of the saturation value, stabilized by a spontaneous
symmetry breaking of
lattice translations with a $\sqrt{3}\times \sqrt{3}$ unit
cell. Regarding the more challenging $m=1/9$ plateau, we find two competing valence bond
crystals depending on the system size, both breaking translation as well as point group
symmetries and with a larger $3\times 3$ unit
cell. Such
quantum states with local modulations of the magnetization average values could be observed experimentally in the near future.
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Materials Science
Quantitative Photoemission Predictions of Semiconducting Photocathodes from Many-Body Ab Initio Theory
Richard Schier, Chen Wang, Jonas Dube et al. (+4 more)
The development of high-performance electron sources requires theoretical frameworks that accurately link the microscopic electronic properties of cathode materials to their macroscopic photoemission observables. Here, we present a many-body extension of the three-step photoemission model for semiconducting photocathodes, directly integrating the $GW$ approximation and the solution of the Bethe-Salpeter equation on top of density functional theory (DFT). This approach overcomes the intrinsic limitations of standard DFT by explicitly accounting for quasiparticle and excitonic effects in the photoexcitation process. The
quantum efficiency (QE) is evaluated by combining the ab initio absorption with an emission probability derived as an
exciton-weighted average. We validate this model on representative alkali antimonides and demonstrate that a qualitative many-body description successfully captures complex spectral features that empirical models fail to reproduce. Furthermore, by incorporating macroscopic optical effects such as thin-film interference and polarization via Fresnel post-processing, we achieve quantitative agreement with experimental QE values without any adjustment. Minor discrepancies near the photoemission threshold are attributed to the idealized surface barrier adopted in the model and
impurity effects in the samples, highlighting specific directions for future refinements. This work establishes a robust, parameter-free ab initio tool that bridges microscopic electronic correlation with macroscopic observables, providing a critical pathway for the rational design of next-generation electron sources.
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All authors Richard Schier, Chen Wang, Jonas Dube, Julius Kühn, Alice Galdi, Thorsten Kamps, Caterina Cocchi
Strongly Correlated Electrons · Cross-listed from physics.chem-ph
Neural Quantum States Based on Selected Configurations
Marco Julian Solanki, Lexin Ding and Markus Reiher
Neural
quantum states (NQS) provide a flexible and highly expressive parameterization of wave functions for strongly correlated problems in
quantum chemistry. Despite rapid advances in network architectures, the evaluation of electronic energies remains almost exclusively based on variational Monte Carlo (VMC). While VMC is effective for structured systems such as
spin chains, its accuracy and efficiency for electronic
Hamiltonians are hindered by sharply peaked distributions,
stochastic gradient noise, and slow convergence with sample size. In this letter, we assess the capability of NQS-VMC to efficiently capture correlation in electronic ground states by comparing it to a recently developed NQS-based selected configuration (NQS-SC) approach. We set up a systematic comparison of the ground-state optimizations obtained with NQS-VMC and NQS-SC for molecular systems dominated by either static or dynamical correlation. The comparison demonstrates a clear advantage of NQS-SC over NQS-VMC in both energy accuracy and wave-function coefficients, particularly for statically correlated molecules. Moreover, NQS-SC exhibits robust systematic improvability, whereas NQS-VMC does not. These findings position NQS-SC as the new default approach over NQS-VMC for electronic structure calculations. We further observe that neither NQS-SC nor NQS-VMC can efficiently capture dynamical correlation, highlighting the need for future hybrid methods, such as multiconfigurational perturbation theories built on top of NQS solutions.
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Materials Science
A molecular-spin photovoltaic device
Xiangnan Sun, Saül Vélez, Ainhoa Atxabal et al. (+6 more)
We fabricated a C60-based molecular
spin photovoltaic device that integrated a photovoltaic response with the
spin transport across the molecular layer. The photovoltaic response can be modified under the application of a small
magnetic field, with a magnetophotovoltage of up to 5% at room temperature. Device functionalities include a
magnetic current inverter and the presence of diverging magnetocurrent at certain illumination levels that could be useful for sensing. Completely
spin-polarized currents could be created by balancing the external partially
spin polarized injection with the photogenerated carriers.
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All authors Xiangnan Sun, Saül Vélez, Ainhoa Atxabal, Amilcar Bedoya-Pinto, Subir Parui, Xiangwei Zhu, Roger Llopis, Fèlix Casanova, Luis E. Hueso
Strongly Correlated Electrons
Diagnosing energy gap in quantum spin liquids via polarization amplitude
Takayuki Yokoyama and Yasuhiro Tada
Identifying whether a many-body ground state is gapped or gapless is a fundamental yet challenging problem, especially in
quantum spin liquids. In this work, we develop a gap-diagnostic scheme based on the polarization amplitude defined via a twist operator, evaluated within the infinite density-
matrix renormalization group (iDMRG) framework. As a
benchmark, analysis of the
spin-$1/2$ XXZ chain demonstrates that the polarization amplitude clearly distinguishes the gapless Tomonaga-Luttinger
liquid from the gapped Néel phase. We then extend this framework to infinite cylinders of the
spin-$1/2$ XY-$J_\chi$ model on the square
lattice. We find that the polarization amplitude sharply detects the transition between the gapless XY phase and the gapped
chiral spin liquid phase. These results show that polarization amplitudes provide a strong energy-gap diagnostic in two-dimensional frustrated
quantum magnets, including
quantum spin liquids.
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Materials Science
High-Tc Superconductivity in Functionalized Out-of-Plane Ordered Double Transition Metal MXenes
Mohammad Keivanloo, Fateme Dinmohammad, Shashi B. Mishra et al. (+10 more)
Two-dimensional (2D)
superconductors attracted growing interest in condensed-matter physics research. In this work, we explore the superconducting properties of surface-functionalized, out-of-plane ordered double transition-metal MXenes (o-MXenes), which exhibit distinctive structural and electronic characteristics. Using first-principles calculations, we investigate the effects of electronic structure, electron-
phonon coupling (EPC), anharmonicity, and anisotropy effect in superconductivity properties of o-MXenes. We examine a wide range of o-MXene systems, M$_{2}$M$^\prime$X$_{2}$T$_{2}$ (M = Mo, W; M$^\prime$ = Sc, Ti, V, Mo, Zr, Nb, Ta; X = C, N), functionalized with F, O, Cl, and H groups. Out of 128 candidates, 32 compounds are found to be mechanically, dynamically, and thermodynamically stable, exhibiting superconducting transition temperatures (T$_{c}$) from 0.1 K to 52 K. Notably, the Mo$_{2}$ScN$_{2}$O$_{2}$ compound achieves the highest T$_{c}$ of 52 K, with a superconducting gap of $\sim$10 meV. Solving the anisotropic Eliashberg equation reveals that Mo$_{2}$ScN$_{2}$O$_{2}$ is an anisotropic two-gap
superconductor, and incorporating anharmonic effects decreases its T$_{c}$ slightly. We further analyze flat-band-induced EPC enhancement and present EPC
matrix elements as functions of
phonon wavevector q for distinct vibrational modes that show anharmonic behavior of these materials.
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All authors Mohammad Keivanloo, Fateme Dinmohammad, Shashi B. Mishra, Mohammad Sandoghchi, Mohammad Javad Arshia, Mitsuaki Kawamura, Elena R. Margine, Muhammad Haris Mahyuddin, Hannes Raebiger, Reza Pamungkas Putra Sukanli, Kenta Hongo, Ryo Maezono, Mohammad Khazaei
Materials Science
Molecular Beam Epitaxy of Al$\mathrm{_{1-x}}$Sc$\mathrm{_{x}}$N Nanowires: Towards Group-III Nitride Piezoelectric Nanogenerators with Enhanced Response
Adriano Notarangelo, Rudeesun Songmuang, Mostafa Saleh et al. (+10 more)
We study the molecular beam epitaxy of self-assembled Al$\mathrm{_{1-x}}$Sc$\mathrm{_{x}}$N nanowires on conductive TiN layers and demonstrate their application in piezoelectric nanogenerators. Wurtzite Al$\mathrm{_{1-x}}$Sc$\mathrm{_{x}}$N nanowires with uniform Sc incorporation are grown across a wide composition range (0<x<0.35). At substrate temperatures below 700 $^\circ{}$C, these nanowires exhibit an inversely tapered morphology, whereas higher temperatures favor the nucleation of additional branches due to a phase separation of Al$\mathrm{_{1-x}}$Sc$\mathrm{_{x}}$N into wurtzite AlN and rock-salt ScN. Phase-pure Al$\mathrm{_{1-x}}$Sc$\mathrm{_{x}}$N nanowires are integrated into vertical nanogenerators, where the metallic TiN substrate serves as bottom electrode. The fabricated
polymer-nanowire composite devices achieve effective piezoelectric charge coefficients of up to 8.5 pC N$^{-1}$ at x=0.32, thus exceeding the piezoelectric response of bulk AlN by nearly a factor of two. Although the charge response remains lower compared to Al$\mathrm{_{1-x}}$Sc$\mathrm{_{x}}$N thin films, the reduced effective dielectric permittivity of the nanowire-
polymer composites compensates the reduction in piezoelectric charge coefficient, eventually yielding a higher voltage response and comparable energy harvesting efficiency. Finally, effective medium modeling reveals that the device architecture is the primary factor limiting performance, providing general design principles for highly efficient nanowire-based piezoelectric energy harvesters.
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All authors Adriano Notarangelo, Rudeesun Songmuang, Mostafa Saleh, Natthawadi Buatip, Ileana Florea, Philippe Vennéguès, Aidan F. Campbell, Hans Tornatzky, Jonas Lähnemann, Thomas Auzelle, Lutz Geelhaar, Oliver Brandt, Philipp M. John
Soft Condensed Matter
Divergent Impact Charging of Polymer Particles
Simon Jantač and Holger Grosshans
When a particle contacts a surface of another material, it is commonly believed that the particle acquires an impact charge that scales inversely with its pre-impact charge and whose polarity is set by the materials. We show that this belief holds for conductive particles but fails for
polymers. For
polymers, the impact charge increases linearly with the particle's pre-impact charge. Its polarity is not determined by the materials but by the pre-impact particle charge relative to a divergence point at which the net charge transfer reverses. We attribute this divergence to the attraction of surrounding ions to the particle surface. These attracted ions carry polarity opposite to that of the particle, and their amount scales with the particle charge. They transfer to the opposing surface during contact, thereby defining the impact charge. We propose a phenomenological model for the divergent impact charge arising from this mechanism. Finally, we reexamine previous measurements and show that they support this mechanism.
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Superconductivity
Limits of Thermal Conductance Quantization in Chiral Topological Josephson Junctions
Daniel Gresta, Fernando Dominguez, Raffael L. Klees et al. (+3 more)
We investigate thermal and non-local electrical transport in four-terminal Josephson junctions formed by a normal region coupled to two transverse
chiral superconducting leads, supporting phases characterized by Chern numbers ${\cal C}=0,\,1$\,and\,2. We identify the conditions under which a single
chiral Majorana mode (${\cal C}=1$) produces a robust half-quantized thermal conductance, while non-local electrical conductance remains strongly suppressed by particle-hole
symmetry. Thermal conductance quantization occurs near a superconducting phase difference $\pi$, but only in the low-doping regime of the central region and in the intermediate- to long-junction limits. At finite Zeeman fields, the thermal response broadly follows the
topology of the isolated superconducting leads for the $C=1$ phase while, in the ${\cal C}=2$ phase, the thermal conductance generally deviates from quantization, depending on the momentum-space location of the Majorana modes. Our results establish clear criteria for probing
chiral Majorana modes in Josephson junctions and highlight the essential role of momentum-space structure, finite-size geometry, and sample parameters in thermal transport.
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All authors Daniel Gresta, Fernando Dominguez, Raffael L. Klees, Florian Goth, Laurens W. Molenkamp, Ewelina M. Hankiewicz
Mesoscale and Nanoscale Physics
Electrostatic edge effects versus edge doping in graphene nanoribbons: a scanning gate microscopy and modelling study
Colm Durkan, Xiao Liu and Ed Saunders
The charge neutrality point (CNP) of
graphene nanoribbons (GNRs) patterned by oxygen
plasma etching moves towards zero as the ribbon narrows and, on 300 nm SiO2, changes sign below a crossover width of ~ 50 nm: an observation previously attributed to n-type edges surrounding a p-type bulk. We test this edge-doping hypothesis in three ways. First, finite element modelling of complete GNR transistors with uniform doping shows that fringing of the gate field at the edges reproduces the trend of the measured CNP with width down to ~ 50nm without any edge doping, while producing a bias-dependent inversion of the carrier type at the edges that mimics n-type edges in scanned-probe measurements. Second, fitting the CNP of ribbons on 90 nm and 300 nm SiO2 with the gate capacitance of a finite strip, which fixes the electrostatic contribution with no adjustable parameter other than the bulk doping, shows that fringing accounts for most of the width dependence and isolates the remainder as an edge charge. This is acceptor-like (0.24 e/nm per edge) in the present ribbons, which therefore have no n-type edges, and donor-like but small in devices on 300 nm SiO2; no single edge-charge, field-coupled or contact-doping mechanism describes both. Third, scanning gate microscopy finds no edge contrast of the sign expected for n-type edges. The width dependence of the CNP is therefore predominantly electrostatic, and n-type edges are not an intrinsic consequence of oxygen-
plasma etching. A design map shows that fringing dominates the width dependence whenever the gate dielectric is thicker than 30-50 nm, whereas in scaled high-K transistors, edge charge dominates and would shift the threshold voltage of a 10 nm ribbon by ~ 0.1-0.15 V. Fitting the CNP versus width with the strip capacitance provides a simple test for edge doping in any gated two-dimensional nanostructure
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Mesoscale and Nanoscale Physics
Non-renormalization of the Hall viscosity of integer and Jain fractional quantum Hall phases by Coulomb interactions
M. Selch
We proof the non-renormalization of the
Hall viscosity by Coulomb interactions for integer and Jain fractional
quantum Hall states in the presence of Galilean invariance building on previous results obtained for the
Hall conductivity. We employ Wigner-Weyl calculus in order to represent the
Hall viscosity in terms of a novel Green function expression supplemented by covariant derivatives. The Green function based expression is derived within the free field theory of electrons and explicitly calculated for this case as well as in the mean field approximation of the composite
fermion theory Jain states employing the model by Lopez and Fradkin. The topological orbital
spin of composite
fermions distinguishes their mean field treatment from that of electrons resulting in an additional topological contribution. We furthermore proof the topological invariance of the newly introduced Green function expression for the
Hall viscosity for the leading contribution in powers of the filling factor with and without Galilean boost
symmetry. The latter condition is known to already imply a
Hall viscosity per emergent quasiparticle number density quantized in units of one half times the average quasiparticle orbital
spin or one quarter times the Wen-Zee shift. The Wen-Zee shift features a contribution from the composite
fermion topological orbital
spin relative to that of electrons which we highlight within our formalism and connect to Haldane's
geometric Hall viscosity framework.
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Other Condensed Matter · Cross-listed from quant-ph
Quantum metrology with partially accessible chaotic sensors
Harshita Sharma, Sayan Choudhury and Jayendra N. Bandyopadhyay
Most
quantum metrology protocols harness highly entangled probe states and globally accessible measurements to surpass the standard
quantum limit. However, it is challenging to satisfy these requirements in realistic many-body sensors. We demonstrate that both of these constraints can be overcome in
quantum chaotic sensors. Crucially, we establish that even in the presence of partial measurement accessibility, chaotic dynamics enables initial unentangled states to exhibit Heisenberg scaling of the
quantum Fisher information, $I_{\alpha}$ with time. In the weakly chaotic regime, we identify
spin-coherent states placed at the edge of the regular islands in the mixed classical phase space as optimal initial states for enhanced sensitivity. On the other hand, in the strongly chaotic regime, $I_{\alpha}$ is insensitive to the choice of the initial state. Notably,
quantum-enhanced sensitivity is achieved even when a very low fraction ($\sim 5\%$) of the
qubits are accessible. These results establish
quantum chaos as a robust resource for
quantum-enhanced sensing under realistic accessibility constraints on accessibility.
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Materials Science
Interface-Driven Growth Mode Control of 2D GaSe on 3D GaAs Substrates with Distinct Crystallographic Orientations
Aida Sheibani, Mohammad Zamani, Charles Paillard et al. (+9 more)
Previous studies of the growth of two-dimensional (2D) gallium selenide (GaSe) by molecular beam epitaxy (MBE) on a gallium arsenide (GaAs) three-dimensional (3D) substrate have reported significant differences in growth morphology, polytype, and the nature of the interface. The results differ, ranging from GaSe 2D film growth at tilted 2D planes to observed spiral structures, thereby calling for a deeper understanding of the impact of the substrate interface on the growth of GaSe films. In this paper, we conduct a comprehensive reexamination of the growth mechanism of GaSe on GaAs substrates with (211)B and (001)B orientations, investigating the nature of the 2D/3D interface and the resulting morphology of the 2D GaSe films. We do this by investigating different methods of preparation of the GaAs substrate surface before the growth of GaSe by MBE, the importance of which has not been considered before. Our results resolve the mechanistic origin of tilted versus non-tilted 2D growth and establish a general interface-driven orientation selection rule linking substrate
symmetry and dangling-bond coordination to layered heteroepitaxy. This framework provides a scalable interface-engineering pathway for deterministic control of layered chalcogenide
heterostructures and enables wafer-scale integration with established
semiconductor device platforms.
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All authors Aida Sheibani, Mohammad Zamani, Charles Paillard, Kanagaraj Moorthi, Fernando Maia de Oliveira, Serhii Kryvyi, Mourad Benamara, Hryhorii Stanchu, Calbi Gunder, Hugh Churchill, Yuriy I. Mazur, Gregory Salamo
Soft Condensed Matter
A Variational Formulation for Deformable Particle Simulations and its Level Set Discrete Element Method Implementation
Thomas Henzel and Konstantinos Karapiperis
We present a deformable Discrete Element Method (DEM) that extends the classical rigid-particle formulation through a reduced-order description of elastic grain-scale deformation. The method hinges on two developments. First, an energetic variational formulation based on the Lagrange–d'Alembert principle extends classical rigid-body dynamics to incorporate particle deformability by
embedding translational, rotational, and deformation degrees of freedom within a unified energetic description. Second, particle deformation is realized within the Level Set DEM formalism through evolving level sets. The framework applies broadly to general particle geometries and
topologies, and supports arbitrary deformation modes. The resulting deformable DEM retains the robustness,
geometric and physical clarity, and scalability of classical DEM, while enabling physically grounded grain-scale deformability at a computational cost of the same order of magnitude as rigid DEM. Comparisons with full finite-element simulations demonstrate excellent agreement at both particle and system scales, establishing a general and extensible variational framework for modeling deformation in particulate systems.
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Materials Science
Dependence of the Mn sticking coefficient on Ga-rich, N-rich, and Ga/N-flux-free conditions in GaN grown by plasma-assisted molecular beam epitaxy
YongJin Cho, Changkai Yu, Huili Grace Xing et al. (+1 more)
This brief report examines the influence of Ga/N flux conditions on Mn incorporation in GaN. Mn-doped GaN layers were grown at 680$^{\circ}$C by molecular beam epitaxy on a Ga-polar GaN(0001) template substrate under Ga-rich, N-rich, and no-flux conditions (i.e., Mn $\delta$ doping). Mn incorporation was highest under N-rich condition, lowest under Ga-rich condition, and intermediate in the absence of Ga and N fluxes. For the growth conditions examined in this study, the corresponding Mn sticking coefficients, relative to that of the N-rich condition, were determined to be 0.31 for no-flux growth and 0.01 for the Ga-rich growth.
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All authors YongJin Cho, Changkai Yu, Huili Grace Xing, Debdeep Jena
Quantum Gases
Shift of the Bose-Einstein condensation transition in the presence of a second atomic species
Pedro M. Gaspar, Vanderlei S. Bagnato and Patricia C. M. Castilho
Atomic interactions play an important role in the properties of ultracold atomic gases. In single component bosonic systems, its effect is already present at the critical point for the Bose-Einstein condensate phase transition by shifting it to lower temperatures as a consequence of effective repulsion between the atoms. When considering atomic bosonic mixtures, interesting effects arise from the competition between intra- and interspecies interactions such as the miscible-immiscible phase transition and the particular case of self-bounded
quantum droplets. In such a scenario, it is natural to expect that these interactions will also affect the critical point of each species composing the mixture. In this paper, we obtain analytical expressions for the critical temperature shift of the phase transition to a Bose-Einstein condensate in the presence of a second species. We treat differently the cases in with the second species is above or below its own critical temperature and apply the obtained relations to the case of a $^{23}$Na-$^{39}$K bosonic mixture which can be realized in current running experimental setups. Our findings can be easily extended to other atomic mixtures trapped by arbitrary conservative traps.
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Materials Science
The role of radiation-induced segregation in defect-phase formation in Ni-Ge and Ni-Si alloys
Amit Verma, Yen-Ting Chang, Marie Charpagne et al. (+2 more)
The interactions between chemical phase fields and structural defects play a key role in the properties of
alloys. We illustrate the importance of these interactions in driven
alloys, where defects are continuously being created, with particular focus on systems where radiation-induced segregation occurs. Specifically, we compare the microstructural
evolution in undersaturated Ni-Si and Ni-Ge
alloys during both 100 keV He and 2 MeV Ti irradiations. While the
equilibrium phase diagrams of these systems are similar, and both systems show strong radiation-induced segregation, the evolving defect structures are remarkably different. Ni-Si reveals a high density of Frank loops, while Ni-Ge shows a complex array of dislocations. Moreover, a Ni3Ge precipitate shell is observed to coat He bubbles, while no segregation of Si is observed at such bubbles. We explain these differences in behaviors to solute drag by interstitial fluxes in Ni-Si vs solute drag by vacancy fluxes in Ni-Ge.
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All authors Amit Verma, Yen-Ting Chang, Marie Charpagne, Pascal Bellon, Robert S. Averback
Disordered Systems and Neural Networks
Lecture notes: From Gaussian processes to feature learning
Moritz Helias, Javed Lindner, Lars Schutzeichel et al. (+1 more)
These lecture notes develop the theory of learning in deep and recurrent neuronal networks from the point of view of
Bayesian inference. The aim is to enable the reader to understand typical computations found in the literature in this field. Initial chapters develop the theoretical tools, such as probabilities, moment and cumulant-generating functions, and some notions of large deviation theory, as far as they are needed to understand collective network behavior with large numbers of parameters. The main part of the notes derives the theory of
Bayesian inference for deep and recurrent networks, starting with the neural network Gaussian process (lazy-learning) limit, which is subsequently extended to study feature learning from the point of view of adaptive kernels. The notes also expose the link between the adaptive kernel approach and approaches of kernel rescaling.
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All authors Moritz Helias, Javed Lindner, Lars Schutzeichel, Zohar Ringel
Materials Science
Exploring Wetting and Optical Properties of CuAg Alloys via Surface Texture Morphology Analysis
Krzysztof Wieczerzak, Grzegorz Cios, Piotr Bała et al. (+2 more)
Copper-silver (CuAg)
alloys are increasingly explored for applications in high-performance electrical and electronic systems, owing to their unique combination of high electrical and thermal conductivity and enhanced mechanical strength. Nevertheless, a thorough understanding of how these
alloys surface characteristics fundamentally influence properties remains largely underdeveloped. Here, we explored the complex interplay between surface texture morphology, layer composition, wetting, and optical properties of Cu, Ag, and CuAg thin films deposited on textured silicon substrates via magnetron sputtering. Employing data mining and machine learning techniques, we identified robust correlations between contact angle and surface fractal dimension across all layer types promoting Cassie-Baxter surface state formation. Our analysis revealed a significant connection between layer thickness and surface topography
entropy deficit, suggesting a dynamic
evolution of surface order/disorder during metal film growth. Furthermore, we observed that contact angle sensitivity to layer thickness implied a correlation with microstructure
evolution. Through K-Means clustering, we successfully categorized the formed surface textures morphology. Finally, a Random Forest regression model was developed to accurately predict water contact angles (Mean Absolute Error around 5 deg) using only texture and optical parameters. The model, along with accompanying Python code, is publicly available. Our findings establish a pathway towards targeted surface texture morphology engineering for tailored material performance.
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All authors Krzysztof Wieczerzak, Grzegorz Cios, Piotr Bała, Johann Michler, Benedykt R. Jany
Mesoscale and Nanoscale Physics
Subcycle videography of lightwave-driven Landau-Zener-Majorana transitions in graphene
Vincent Eggers, Giacomo Inzani, Manuel Meierhofer et al. (+14 more)
Strong light fields have unlocked previously unthinkable possibilities to tailor coherent electron trajectories, engineer band structures and shape emergent phases of matter all-optically. Unravelling the underlying
quantum mechanisms requires a visualisation of the lightwave-driven electron motion directly in the band structure. While photoelectron momentum microscopy has imaged optically excited electrons averaged over many cycles of light, actual subcycle band-structure videography has been limited to small electron momenta. Yet lightwave-driven elementary processes in
quantum materials often occur throughout momentum space. Here, we introduce attosecond-precision, subcycle band-structure videography covering the entire first Brillouin zone (BZ) and visualize one of the most fundamental but notoriously elusive strong-field processes: non-adiabatic Landau-Zener-Majorana (LZM) tunnelling. The interplay of field-driven acceleration within the Dirac-like band structure of
graphene and periodic LZM interband tunnelling manifest in a coherent displacement and distortion of the momentum distribution at the BZ edge. The extremely non-thermal electron distributions also allow us to disentangle competing scattering processes and assess their impact on coherent electronic control through electron redistribution and thermalization. Our panoramic view of strong-field-driven electron motion in
quantum materials lays the foundation for a microscopic understanding of some of the most discussed light-driven phenomena in condensed matter physics.
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All authors Vincent Eggers, Giacomo Inzani, Manuel Meierhofer, Lasse Münster, Jakob Helml, Robert Wallauer, Sarah Zajusch, Suguru Ito, Leon Machtl, Hao Yin, Christian Kumpf, François C. Bocquet, Changhua Bao, Jens Güdde, F. Stefan Tautz, Rupert Huber, Ulrich Höfer
Soft Condensed Matter
Nanoscale Electroviscous Lift Force
Hao Zhang, Zaicheng Zhang, Thomas Guérin et al. (+1 more)
About forty years ago, it was predicted that a charged particle, moving parallel to a charged wall in an electrolyte, should experience a lift force that, contrarily to electrostatic forces, is not screened at large distances. Up to now, such electroviscous lift force has not been directly measured. Here, we use Atomic Force Microscopy to directly measure the electroviscous lift force and quantify its dependency with the distance to the wall, the translation velocity or the particle's size. Observing that existing theories exhibit large discrepancies with our experimental observations, we develop an analytical approach combining lubrication theory to a previously introduced formalism for small screening length. The experimentally observed lift forces are in good agreement with our theoretical predictions and reveal, for the first time, a saturation of the lift force for increasing velocities. Altogether, our results characterize, through direct measurements and analytical approach, the properties of electroviscous forces between charged particles in viscous electrolytes in non-
equilibrium conditions.
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All authors Hao Zhang, Zaicheng Zhang, Thomas Guérin, Abdelhamid Maali
Mesoscale and Nanoscale Physics
Nonparabolic dispersion of charge carriers in CsPbI$_3$ in the orthorhombic phase
O. S. Sultanov D. K. Loginov, I. V. Ignatiev, D. V. Pankin et al. (+2 more)
The dispersion curves for the electrons and holes in CsPbI$_3$ in the orthorhombic phase are calculated using the density functional theory (DFT), with the
spin-orbit coupling taken into account. The effective masses of the charge carriers are obtained using the
parabolic approximation of the dispersion curves in different directions in the $k$-space. It is found that the dispersion curves demonstrate strong nonparabolicity at energies above 0.2 eV for electrons and above 0.1 eV for holes, available for experimental study by the means of optical spectroscopy. We propose a model that describes the dispersion dependences of charge carriers at those energies, where the effective masses of the quasiparticles depend quadratically on the wave vector. An expression is obtained according to the model, which can accurately approximate the dispersion curves for the electron and the hole in all symmetric directions from the center to the boundary of the Brillouin zone.
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All authors O. S. Sultanov D. K. Loginov, I. V. Ignatiev, D. V. Pankin, M. B. Smirnov, M. S. Kuznetsova
Soft Condensed Matter
Investigating Disordered Granular Matter via Ordered Geometric Fragmentation
Malkhazi A. Meladze
The
evolution of occupied volume under progressive fragmentation of granular matter is studied using a purely
geometric model. Rather than modelling disorder directly, properties are investigated by analysing highly ordered reference configurations that provide sharp upper bounds on accessible volume. Grains are idealised as fragments from a hypothetical elongated parent prism with square cross section, sequentially sliced and reassembled into configurations that maximise enclosed volume. Analytic expressions are derived for the maximal volume at each fragmentation stage. Volume
evolution is non-monotonic: initial fragmentation produces structures exceeding the original volume, while further fragmentation leads to monotonic decrease converging to 5/4 times the initial volume, independent of fragment number. The packing fraction obeys the asymptotic scaling law of inverse proportionality to aspect ratio, in agreement with experimental observations. The model reveals pairs of configurations built from geometrically indistinguishable building blocks yet enclosing different volumes. These conjugate configurations constitute
geometric analogues of distinct phases connected by rearrangement-induced transitions. A criterion for observability is derived, showing such transitions are restricted to systems of limited grain number but may occur locally as domain formation in larger assemblies. Comparison with experimental data confirms the model provides a lower bound on packing fraction and predicts domain sizes should scale linearly with aspect ratio, testable through X-ray
tomography.
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