Mesoscale and Nanoscale Physics
Topological surface-state destruction via trivializing proximity effect: Lattice localization despite continuum criticality
Arthur Niwazuki and Matthew S. Foster
In a significant conceptual revision to the tenfold classification scheme for topological
insulators and
superconductors, it was recently demonstrated that most three-dimensional (3D) classes are simultaneously "localizable" in two distinct, but intricately connected ways: (1) There is no obstruction to Wannier localization of all bulk eigenstates, and (2) Almost all surface states can be Anderson localized by arbitrarily weak
symmetry-preserving quenched disorder. Here we consider the localizable class CI in 3D, and numerically investigate the stability of surface states. We demonstrate that surface states of a bulk class-CI topological
lattice model are fragile in that they can be Anderson localized by the combination of weak quenched randomness and hybridization with an additional trivial 2D band (a trivializing proximity effect, TPE). With the TPE, stronger disorder is more destructive to the surface states of the bulk
lattice model. By contrast, without additional bands the surface states remain extended, exhibiting robust spectrum-wide
quantum criticality. We also investigate the fragility of surface states in effective 2D class-CI continuum Dirac theories, including the
chiral limit of the Bistritzer-MacDonald model for twisted
bilayer graphene. Although the continuum models exhibit signs of Anderson localization near gap edges for weak disorder, stronger disorder instead appears to heal the surface, restoring criticality whilst filling in spectral energy gaps. Our results provide further evidence that effective continuum field theories fail to capture key aspects of surface-state physics in localizable topological phases.
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Strongly Correlated Electrons · Cross-listed from hep-th
On decoding the string from interfaces in 2d conformal field theories
Avik Banerjee, Tanay Kibe, Ayan Mukhopadhyay et al. (+1 more)
General solutions of a gravitational junction between two copies of a three-dimensional Einstein
manifold $\mathcal{M}$ correspond to the solutions of the non-linear Nambu-Goto equation for a string in $\mathcal{M}$. We show that, for the junctions in three-dimensional anti-de Sitter spacetimes constituted by tensile strings, which are dual to interfaces between thermal states in conformal field theories, the solutions of the Nambu-Goto equation describing the junction correspond to wave-packets, which are perfectly reflected at the interface to future null infinity without shape distortion when incident from past null infinity. These wavepackets are realized by half-sided conformal transformations and affect the expectation value of the displacement operator. We further show that the
entanglement entropy of an interval straddling the interface deciphers the stringy modes of the dual junction even in the tensionless limit. We also demonstrate that the strong sub-additivity of
entanglement entropy is satisfied and is saturated for symmetric intervals generally.
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All authors Avik Banerjee, Tanay Kibe, Ayan Mukhopadhyay, Giuseppe Policastro
Strongly Correlated Electrons
Topological BF Theory construction of twisted dihedral quantum double phases from spontaneous symmetry breaking
Zhi-Qiang Gao, Chunxiao Liu and Joel E. Moore
Nonabelian topological orders host exotic anyons central to
quantum computing, yet established realizations rely on case-by-case constructions that are often conceptually involved. In this work, we present a systematic construction of nonabelian dihedral
quantum double phases based on a continuous $O(2)$ gauge field. We first formulate a topological $S[O(2)\times O(2)]$ BF theory, and by identifying the Wilson loops and twist operators of this theory with anyons, we show that our topological BF theory reproduces the complete anyon data, and can incorporate all Dijkgraaf–Witten twists. Building on this correspondence, we present a microscopic model with $O(2)$
lattice gauge field coupled to Ising and rotor matter whose Higgsing yields the desired dihedral
quantum double phase. A perturbative renormalization group analysis further suggests a direct transition from this phase to a $U(1)$ Coulomb or
chiral topological phase at a stable multicritical point with emergent $O(3)$
symmetry. Our proposal offers an alternative route to nonabelian topological order with promising prospects in synthetic gauge field platforms.
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Mesoscale and Nanoscale Physics
Imaging Quantum Well States of Dirac Electrons in Exfoliated 3D Topological Insulators
Shreyashi Sinha, Shantanu Pathak, Saswata Bhattacharya et al. (+1 more)
We present a controlled mechanical exfoliation technique for bulk 3D topological
insulators that yields atomically clean ultrathin flakes, enabling
quantum well states (QWS) of Dirac electrons to be clearly resolved. Achieving reliable fabrication of pristine, high-quality two-dimensional layers suitable for atomic-scale spectroscopy remains a central experimental challenge in uncovering their emergent
quantum states and realizing device-relevant functionalities. Atomically resolved scanning probe microscopy and micro-Raman spectroscopy reveal a strong correlation between Raman intensity and film thickness, enabling rapid identification of (Bi\textsubscript{0.1}Sb\textsubscript{0.9})\textsubscript{2}Te\textsubscript{3} flakes with desired thickness. High resolution scanning tunneling spectroscopy on exfoliated flakes with atomically flat terraces reveals QWS, driven by
quantum confinement of Dirac electrons. This effect is rarely observed due to the electrons resistance to electrostatic confinement caused by Klein tunneling. The standard phase accumulation model accurately captures the characteristics of QWS and extracts the electronic band dispersion, showing excellent agreement with density functional theory calculations. Band structure calculation reveals that with increasing
quantum-layer thickness, the interlayer coupling enhances the electronic dispersion, progressively reducing subband splitting and giving rise to bulk-like continuous bands. Spatially resolved spectroscopy around surface defects further confirms that QWS of Dirac electrons in topological
insulators remains robust against defect scattering. This work paves the way for exploring diverse
quantum phenomena and device applications through
quantum confinement, surface-state engineering, and tunable topological phases.
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All authors Shreyashi Sinha, Shantanu Pathak, Saswata Bhattacharya, Sujit Manna
Strongly Correlated Electrons
Pair density wave in the fractional quantum Hall effect at even denominator
M. V. Milovanović
The fractional
quantum Hall effect (FQHE) at filling 5/2, which is usually understood as a $p$-wave paired state of underlying quasiparticles - composite
fermions, transforms into a nematic phase under pressure \cite{csathy0, csathy}. A pair density wave (PDW) may be a precursor, underlying state for this behaviour, and such state(s) were proposed that maintain the weak-pairing feature of the uniform paired state \cite{frad}. Based on considerations in the weak-coupling regime of a microscopic description of the pairing phase (to mimic the phase as it gives way to a nematic phase in the experiments), we argue that the ensuing and relevant PDW state has a strong-pairing character. Furthermore, due to the existence of a single collective mode associated with the order parameter in the uniform paired phase, in the weak-coupling regime, the $p$-wave paired state, in general (for example, in the superconducting state of electrons), may be prone to a PDW instability.
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Soft Condensed Matter
Cross-linked pair of polymer chains under strong tension
Geunho Noh and Panayotis Benetatos
We study two cross-linked
polymer systems in the strong stretching regime. The first consists of two
polymers sharing one endpoint, with the other two endpoints coupled by a harmonic potential. Within the weakly bending approximation, we analyze the tensile elastic response for freely jointed or wormlike chains; for the latter, the approximation applies either at large tension or at moderate tension with large persistence length (rodlike limit). We obtain analytic expressions for the force–extension relation and for the longitudinal and transverse mismatch of the cross-linked endpoints. In the thermodynamic limit, the cross-link does not affect the tensile elasticity, but it significantly suppresses transverse fluctuations, effectively forming a loop structure. The second system is a
polymer necklace in the thermodynamic limit, composed of two strongly stretched
polymers interconnected by a regular sequence of reversible cross-links. Using an analogy with a two-dimensional system of concatenated Gaussian loops ("Gaussian slinky"), we calculate the mean fraction of cross-linked sites as a function of the tensile force and find weak and strong binding regimes connected by a crossover. For shallow binding potential wells (compared with $k_{\rm{B}}T$), we employ a continuum description and exploit the mapping between directed
polymers and a two-dimensional
quantum particle to determine the crossover behavior and the mean transverse separation between the two
polymer chains.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.app-ph
Robotic chip-scale nanofabrication for superior consistency
Felix M. Mayor, Wenyan Guan, Erik Szakiel et al. (+2 more)
Unlike the rigid, high-volume automation found in industry, academic research requires process flexibility that has historically relied on variable manual operations. This hinders the fabrication of advanced, complex devices. We propose to address this gap by automating these low-volume, high-stakes tasks using a robotic arm to improve process control and consistency. As a proof of concept, we deploy this system for the resist development of Josephson junction devices. A statistical comparison of the process repeatability shows the robotic process achieves a resistance spread across chips close to 2%, a significant improvement over the ~7% spread observed from human operators, validating robotics as a solution to eliminate operator-dependent variability and a path towards industrial-level consistency in a research setting.
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All authors Felix M. Mayor, Wenyan Guan, Erik Szakiel, Amir H. Safavi-Naeini, Samuel Gyger
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Entanglement-limited linear response in fermionic systems
Hadi Cheraghi, Ali G. Moghaddam and Teemu Ojanen
We propose a general connection between
entanglement-
entropy scaling laws and the linear response functions of particle-conserving fermionic systems in their ground state. Specifically, we show that the response to perturbations coupled to the particle number within a finite region exhibits the same size scaling as the
entanglement entropy of that region. We explicitly verify this scaling in free-
fermion systems that display area-law, volume-law, and critical forms of
entanglement. The resulting
entanglement-governed scaling of response functions leads to unexpected physical consequences. For instance, contrary to conventional expectations, the energy absorption rate and particle-number fluctuations in gapped systems scale with the boundary of the perturbed region rather than with its volume. Our work thus establishes a direct link between linear-response properties and many-body
entanglement.
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Strongly Correlated Electrons
Chiral spin liquid instability of the Kitaev honeycomb model with crystallographic defects
Arnab Seth, Fay Borhani and Itamar Kimchi
We study the
spin-1/2 Kitaev honeycomb gapless
spin liquid in the presence of Stone-Wales-type local
lattice defects with odd-sided plaquettes. While the clean Kitaev model has no finite-temperature phase transitions, we find that introducing a finite defect density $n_d\approx 10^{-4}$–$10^{-2}$ produces a true phase transition with a sizeable $T_c \approx 2 n_d$ in units of the Kitaev exchange. The resulting non-Abelian
chiral quantum spin liquid exhibits scalar
spin chirality and electron orbital magnetization which peak near
lattice defects. This disorder-driven instability relies on an emergent long range
ferromagnetic interaction $r^{-\gamma}$ ($\gamma \approx 2.7$) between defect chiralities, mediated by the nearly-gapless
fermions, with implications for
topology generation in Dirac cones with fluctuating mass terms.
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Soft Condensed Matter
Evolution of the contact between rough viscoelastic solids after decreasing loads: memory erasure and monotonic increase
Zichen Li, Renald Brenner and Lucas Frérot
The real area of contact governs, in part, the magnitude of the friction force, yet its time
evolution in rough viscoelastic interfaces remains incompletely understood. In experiments of contact between polymethylmethacrylate blocks under decreasing normal loads, Dillavou and Rubinstein have shown that the true contact area exhibits, after unloading, a decreasing phase and long-term
memory of the contact state prior to unloading. It is however unclear what modeling ingredients are necessary to reproduce these two features. Here, we investigate these effects using fractional viscoelastic rough contact models. By adapting existing contact theories and numerical simulation methods to fractional viscoelasticity, which induces a wide relaxation spectrum, we reproduce logarithmic aging under constant load, but show that
memory of the contact state is erased upon unloading. Indeed, the contact area behaves as if it had always experienced the reduced load, even on short time-scales, contrasting with the response of a standard linear solid. Moreover, none of our results show a decreasing regime of the contact area after unload: we ultimately prove that this is the case for all linear viscoelastic models – despite capturing logarithmic aging – leading to the conclusion that additional local internal variables are required to explain both long-term contact
memory and contact area reduction after unloading.
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Strongly Correlated Electrons
Kondo screening and random-singlet formation in highly disordered systems
Lucas G. Rabelo, Igor C. Almeida, Eduardo Miranda et al. (+2 more)
We introduce a minimal effective framework designed to address the anomalous low-temperature thermodynamics observed in strongly disordered interacting systems near a metal-
insulator transition, such as doped
semiconductors. Our approach examines how a strongly inhomogeneous electronic bath quenches dilute pairs of local
magnetic moments. By solving the resulting two-
impurity Kondo-Heisenberg problem within a large-$\mathcal{N}$ variational framework, we capture the competition between Kondo screening and random-singlet formation. Both mechanisms give rise to singular thermodynamic responses, producing a
magnetic susceptibility of the form $\chi(T)\sim T^{-\alpha}$, where the exponent $\alpha$ evolves smoothly with model parameters and saturates in the metallic regime, consistent with experimental observations. Our results establish a unified framework that connects random-singlet physics and disorder-induced Kondo screening in strongly disordered correlated materials.
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All authors Lucas G. Rabelo, Igor C. Almeida, Eduardo Miranda, Vladimir Dobrosavljević, Eric C. Andrade
Materials Science
Artificial Intelligence Driven Workflow for Accelerating Design of Novel Photosensitizers
Hongyi Wang, Xiuli Zheng, Weimin Liu et al. (+2 more)
The discovery of high-performance photosensitizers has long been hindered by the time-consuming and resource-intensive nature of traditional trial-and-error approaches. Here, we present AI-Accelerated PhotoSensitizer Innovation (AAPSI), a closed-loop workflow that integrates expert knowledge, scaffold-based molecule generation, and
Bayesian optimization to accelerate the design of novel photosensitizers. The scaffold-driven generation in AAPSI ensures structural novelty and synthetic feasibility, while the iterative AI-experiment loop accelerates the discovery of novel photosensitizers. AAPSI leverages a curated database of 102,534 photosensitizer-solvent pairs and generate 6,148 synthetically accessible candidates. These candidates are screened via graph
transformers trained to predict singlet oxygen
quantum yield ($\phi_\Delta$) and absorption maxima ($\lambda_{max}$), following experimental validation. This work generates several novel candidates for photodynamic therapy (PDT), among which the hypocrellin-based candidate HB4Ph exhibits exceptional performance at the Pareto frontier of high
quantum yield of singlet oxygen and long absorption maxima among current photosensitizers ($\phi_\Delta$=0.85, $\lambda_{max}$=650nm).
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All authors Hongyi Wang, Xiuli Zheng, Weimin Liu, Zitian Tang, Sheng Gong
Strongly Correlated Electrons · Cross-listed from quant-ph
Simulating dynamics of the two-dimensional transverse-field Ising model: a comparative study of large-scale classical numerics
Joseph Vovrosh, Sergi Julià-Farré, Wladislaw Krinitsin et al. (+11 more)
The
quantum dynamics of many-
qubit systems is an outstanding problem that has recently driven significant advances in both numerical methods and programmable
quantum processing units. In this work, we employ a comprehensive toolbox of state-of-the-art numerical approaches to classically simulate the dynamics of the two-dimensional transverse field Ising model. Our methods include three different tensor network techniques –
matrix product states, tree-tensor networks, and two-dimensional tensor-networks under the belief propagation approximation – as well as time-dependent variational Monte Carlo with Neural
Quantum States. We focus on two paradigmatic dynamical protocols: (i)
quantum annealing through a critical point and (ii) post-quench dynamics. Our extensive results show the quantitative predictions of various state-of-the-art numerical methods providing a
benchmark for future numerical investigations and experimental studies with the aim to push the limitations on classical and QPUs. In particular, our work connects classical simulability to different regimes associated with
quantum dynamics in Rydberg arrays - namely, quasi-adiabatic dynamics, the Kibble-Zurek mechanism, and
quantum quenches.
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All authors Joseph Vovrosh, Sergi Julià-Farré, Wladislaw Krinitsin, Michael Kaicher, Fergus Hayes, Emmanuel Gottlob, Augustine Kshetrimayum, Kemal Bidzhiev, Simon B. Jäger, Markus Schmitt, Joseph Tindall, Constantin Dalyac, Tiago Mendes-Santos, Alexandre Dauphin
Materials Science · Cross-listed from physics.comp-ph
Electrified Metal-Water Interfaces at Constant Potential: Data-Efficient Transfer Learning for Machine-Learning-Based Molecular Dynamics
Michele Giovanni Bianchi, Michele Re Fiorentin, Francesca Risplendi et al. (+4 more)
Simulating electrified metal-water interfaces with explicit solvent under constant potential is essential for understanding electrochemical processes, yet remains prohibitively expensive with ab initio methods. We present TRECI, a data-efficient workflow for constructing machine learning force-fields (ML-FFs) that achieve ab initio-level accuracy in electronically grand-canonical molecular dynamics. By leveraging transfer learning from general-purpose and domain-specific models, TRECI enables stable and accurate simulations across a wide potential range using a reduced number of reference configurations. This efficiency allows the use of high-level meta-GGA functionals and rigorous surface-electrification schemes. Applied to Cu(111)-water, models trained on just one thousand configurations yield accurate molecular dynamics simulations, capturing bias-dependent solvent restructuring effects not previously reported. TRECI offers a general strategy for characterising diverse materials and interfacial chemistries, significantly lowering the cost of realistic constant-potential simulations and expanding access to quantitative electrochemical modelling.
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All authors Michele Giovanni Bianchi, Michele Re Fiorentin, Francesca Risplendi, Candido Fabrizio Pirri, Michele Parrinello, Luigi Bonati, Giancarlo Cicero
Materials Science
High-throughput validation of phase formability and simulation accuracy of Cantor alloys
Changjun Cheng, Daniel Persaud, Kangming Li et al. (+7 more)
High-throughput methods enable accelerated discovery of novel materials in complex systems such as high-
entropy alloys, which exhibit intricate phase stability across vast compositional spaces. Computational approaches, including Density Functional Theory (DFT) and calculation of phase diagrams (CALPHAD), facilitate screening of phase formability as a function of composition and temperature. However, the integration of computational predictions with experimental validation remains challenging in high-throughput studies. In this work, we introduce a quantitative confidence metric to assess the agreement between predictions and experimental observations, providing a quantitative measure of the confidence of machine learning models trained on either DFT or CALPHAD input in accounting for experimental evidence. The experimental
dataset was generated via high-throughput in-situ synchrotron X-ray diffraction on compositionally varied FeNiMnCr
alloy libraries, heated from room temperature to ~1000 {\deg}C. Agreement between the observed and predicted phases was evaluated using either temperature-independent phase classification or a model that incorporates a temperature-dependent probability of phase formation. This integrated approach demonstrates where strong overall agreement between computation and experiment exists, while also identifying key discrepancies, particularly in FCC/BCC predictions at Mn-rich regions to inform future model refinement.
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All authors Changjun Cheng, Daniel Persaud, Kangming Li, Michael J. Moorehead, Natalie Page, Christian Lavoie, Beatriz Diaz Moreno, Adrien Couet, Samuel E Lofland, Jason Hattrick-Simpers
Other Condensed Matter · Cross-listed from physics.optics
Scattering in Time-Varying Drude-Lorentz Models
Bryce Dixon, Calvin M. Hooper, Ian R. Hooper et al. (+1 more)
Motivated by recent experiments, the theoretical study of wave propagation in time varying materials is of current interest. Although significant in nearly all such experiments, material dispersion is commonly neglected in theoretical studies. Yet, as we show here, understanding the precise microscopic model for the material dispersion is crucial for predicting experimental outcomes. Here we study the temporal scattering coefficients of four different time-varying Drude-Lorentz models, exploring how an incident continuous wave splits into forward and backward waves due to an abrupt change in
plasma frequency. The differences in the predicted scattering are unique to time-varying media, and arise from the exact way in which the time variation appears in the various model parameters. We verify our results using a custom finite difference time domain
algorithm, concluding with a discussion of the limitations that arise from using these models with an abrupt change in
plasma frequency.
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All authors Bryce Dixon, Calvin M. Hooper, Ian R. Hooper, Simon A. R. Horsley
Strongly Correlated Electrons
Diagnosis of mixed-state topological phases in strongly correlated systems via disorder parameters
Shao-Hang Shi, Xiao-Qi Sun and Zi-Xiang Li
Characterizing topological phases for strongly interacting
fermions in the mixed-state regime remains a major challenge. Here we introduce a general and numerically efficient framework to diagnose mixed-state topological phases in strongly interacting systems via the disorder parameter (DP) of the U(1) charge operator. Specifically, from the finite-size scaling of the second derivative of the DP generating function, we introduce the topological scaling indicator, which exhibits a characteristic linear scaling with the system's linear dimension for topological phases, a signature that vanishes upon transition into a topologically trivial phase. Crucially, we develop an efficient determinant
Quantum Monte Carlo
algorithm that facilitates the evaluation of this indicator in interacting systems. We apply our approach to two paradigmatic models: for the Kane-Mele-Hubbard model, we successfully map the interaction-driven transition from a
quantum spin Hall insulator to a trivial Mott
insulator. Furthermore, our method circumvents the limitations imposed by the severe sign problem in the Haldane-Hubbard model, enabling robust identification of the
quantum anomalous
Hall phase at accessible temperatures. This work provides a powerful and accessible tool for the numerical exploration of topological phenomena in interacting mixed states, opening a pathway to study systems previously inaccessible due to computational obstacles.
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Materials Science
E-coherent crystalline interfaces: coherency enhanced by discohesion arrays
Ryan B. Sills, Alejandro Hinojos, Trevor J. Murray et al. (+3 more)
Coherent crystalline interfaces form when a pair of joined
crystals share
lattice sites. Such interfaces are ubiquitous in materials, minerals, and compounds, with examples including grain boundaries in polycrystals and phase boundaries in multi-phase systems. Existing methodologies such as the topological model provide a framework for understanding the nature of coherency between two
crystals and the line defect content within an interface. However, these methods only consider states of coherency achieved via affine transformations. Here we show that in some interfaces, local relaxations in the form of non-affine transformations lead to the introduction of additional coincidence sites within the interface; we term this class of interfaces as e-coherent. These non-affine relaxations are topologically equivalent to inserting disconnection (or disclination) dipoles or loops into the interface. Unlike traditional interfacial line defects, the defects associated with e-coherency cannot have long-range stress fields and their motion alters the state of coherency between the
crystals. Given these unique properties, we differentiate them from other defects by referring to them as discohesions. Through atomistic simulations and transmission electron microscopy, we show that the energetics and kinetics of e-coherent interfaces are strongly affected by the discohesion content in the interface, leading to fundamentally different behaviors compared to non-e-coherent interfaces. We demonstrate e-coherency in grain, twin, and phase boundaries, and that a given interface can have multiple possible e-coherent states. These results suggest that e-coherency is likely to be pervasive in crystalline solids.
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All authors Ryan B. Sills, Alejandro Hinojos, Trevor J. Murray, Shane H. Cooley, Xiaowang W. Zhou, Douglas L. Medlin
Statistical Mechanics
Tilings of a bounded region of the plane by maximal one-dimensional tiles
Eduardo J. Aguilar, Valmir C. Barbosa, Raul Donangelo et al. (+2 more)
We study the tiling of a two-dimensional region of the plane by $K$-
cell one-dimensional tiles, or $K$-mers. Unlike previous studies, which typically allowed for one single value of $K$ or sometimes a small assortment of fixed values, here a tiling may concomitantly employ $K$-mers comprising any number $K$ of
cells, provided a maximality constraint is satisfied. In essence, this constraint requires each of the $K$-mers in use to be as lengthy as possible, given its surroundings in the resulting tiling. Maximality aims to limit the variety of possible tilings while allowing for interesting behavior in terms of the statistical physical observables of interest. In fact, by introducing an energy function based on
cell contacts and parameterizing it appropriately, we have been able to observe relatively unexpected behavior, including the suggestion of phase transitions as the system's temperature evolves.
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All authors Eduardo J. Aguilar, Valmir C. Barbosa, Raul Donangelo, Welles A. M. Morgado, Sergio R. Souza
Materials Science
What is the signature of a trion in photoemission?
Jinyuan Wu, Zachary H. Withers, Thomas K. Allison et al. (+1 more)
Recent advances in time- and angle-resolved photoemission spectroscopy (tr-ARPES) allow for the probing of multiparticle excited-states in reciprocal space. While neutral two-particle excitations (
excitons) have been observed in tr-ARPES, signatures of trions – three-quasiparticle bound states – have only been probed via optical spectroscopy. Here, we develop a general theory for the ARPES signature of trions in the model system of a monolayer transition metal dichalcogenide (TMD). We simulate the ARPES signals of both positively and negatively charged trions and show that the interaction of the residual holes, or electron and hole, lead to large energy shifts, on the order of the
exciton binding energy, compared to the
exciton signal. For positive trions, the additional momentum degree of freedom of the residual particles removes any strict lower bound on the photoemission energy, leading to distinctive asymmetric spectral features. For negative trions, the photoemission process causes the tr-ARPES spectrum to reproduce inverted images of the
exciton band structure for multiple
exciton states, encompassing both
spin-allowed and
spin-forbidden states, providing a direct momentum-resolved probe of both trion and
exciton physics.
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All authors Jinyuan Wu, Zachary H. Withers, Thomas K. Allison, Diana Y. Qiu
Mesoscale and Nanoscale Physics
Spin-Flux Skyrmions: Anomalous Electron Dynamics and Spin-Hall Currents
Sandip Bera and Sajeev John
We introduce a topologically distinct skyrmion, termed a
spin-flux skyrmion, which shares the same real-space magnetization profile as a conventional skyrmion but differs fundamentally in its underlying topological structure. This distinction originates from the path traced by its rotation
matrices within the doubly connected SO(3) group
manifold, leading to a nontrivial spinor phase of $e^{i\pi}$ upon encircling the texture. Using an explicit SU(2) gauge field formalism, we derive the emergent
magnetic field components generated by both conventional and
spin-flux skyrmions. While conventional skyrmions exhibit a dominant $\sigma_z$ component with weak dipolar $\sigma_x, \sigma_y$ contributions,
spin-flux skyrmions possess an additional monopolar $\sigma_x$ component that yields a finite average emergent field for a finite density of skyrmions. This nontrivial component introduces a nontrivial term in the
Hall conductivity, enabling a direct explanation of experimental
Hall resistivity anomalies that cannot be accounted for by conventional skyrmions alone. Moreover, we show that this additional term couples to the in-plane
spin polarization of conduction electrons, providing a further tunable handle to control the transverse
Hall response.
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Materials Science
Communication: Modeling layered mosaic perovskite alloy microstructures across length scales via a packing algorithm
Murray Skolnick and Salvatore Torquato
Layered "mosaic" metal-halide perovskite materials display a wide-variety of microstructures that span the order-disorder spectrum and can be tuned via the composition of their constituent B-site octahedral species. Such materials are typically modeled using computationally expensive ab initio methods, but these approaches are greatly limited to small sample sizes. Here, we develop a highly efficient hard-particle packing
algorithm to model large samples of these layered complex
alloys that enables an accurate determination of the geometrical and topological properties of the B-site arrangements within the plane of the inorganic layers across length scales. Our results are in good agreement with various experiments, and therefore our
algorithm bypasses the need for full-blown ab initio calculations. The accurate predictive power of our
algorithm demonstrates how our minimalist hard-particle model effectively captures complex interactions and dynamics like incoherent thermal motion, out of plane octahedral tilting, and bond compression/stretching. We specifically show that the composition-dependent miscibility predicted by our
algorithm for certain silver-iron and copper-indium layered
alloys are consistent with previous experimental observations. We further quantify the degree of mixing in the simulated structures across length scales using our recently developed sensitive "mixing" metric. The large structural snapshots provided by our
algorithm also shed light on previous experimentally measured
magnetic properties of a copper-indium system. The generalization of our
algorithm to model 3D perovskite
alloys is also discussed. In summary, our packing model and mixing metric enable one to accurately explore the enormous space of hypothetical layered mosaic
alloy compositions and identify materials with potentially desirable optoelectronic and
magnetic properties.
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Materials Science
Velocity dependence of kinetic friction by multi-scale Quantum Mechanics/Green's Function molecular dynamics
Alberto Pacini, Seiji Kajita, Gabriele Losi et al. (+1 more)
Atomistic simulations are powerful tools for investigating tribological phenomena at a fundamental level; however, simulating a tribological system remains challenging due to the multiscale nature of frictional processes. Recently, we introduced a hybrid method, QM-GF, that enables an accurate description of both interfacial chemistry and phononic dissipation in semi-infinite bulks. In this work, we apply this simulation scheme to study the dependence of kinetic friction on sliding velocity. Using a prototypical diamond interface with varying hydrogen coverages, we find that the friction force decreases with increasing sliding velocity, revealing two distinct sliding regimes at low and high speeds. We provide a physical interpretation of this velocity dependence based on the modulation of the frictional force by the sliding motion over the periodic potential energy surface of the interface. High velocities lead to force cancellation, while low velocities result in a net frictional force characterized by a distinctive sawtooth profile.
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All authors Alberto Pacini, Seiji Kajita, Gabriele Losi, Maria Clelia Righi
Other Condensed Matter · Cross-listed from quant-ph
Synchronized Aharonov-Bohm Motifs via Engineered Dissipation
Christopher W. Wächtler and Gloria Platero
The interplay between external gauge fields and
lattice geometry can induce extreme localization dynamics through complete destructive interference. We show that combining this flux-induced localization with engineered dissipation leads to robust
spin synchronization in rotationally symmetric
spin geometries, referred to as Aharonov-Bohm motifs, with cyclic
symmetries of any order. The synchronized dynamics is independent of initial conditions and features
entanglement among
spins within each motif. We further demonstrate that multiple motifs can fully synchronize when coupled, which is achieved by applying additional collective dissipation acting on all intra-motif
spins. These results reveal a direct connection between flux-induced localization, dissipative engineering, and collective
quantum synchronization.
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Superconductivity
Compact stationary fluxons in the Josephson junction ladder
Andrii O. Prykhodko, Ivan O. Starodub and Yaroslav Zolotaryuk
Stationary compact fluxon profiles are shown to be exact solutions of the inductively coupled and dc-biased Josephson junction ladder. Such states do not exist in the parallel Josephson junction array which is described by the standard discrete sine-Gordon equation. It is shown that there are compact fluxon and multi-fluxon states which either satisfy the top-bottom antisymmetry or are asymmetric. The anti-symmetric states have zero energy if their topological charge is even and the asymmetric states always have zero energy. Depending on the anisotropy constant the compact fluxons can either coexist with the non-compact states or only compact states are possible. External
magnetic field prevents compact state existence.
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Strongly Correlated Electrons
Abhishek Karna, Hansen S. Wu, Shailesh Chandrasekharan et al. (+1 more)
Quantum Monte Carlo methods are powerful tools for studying
quantum many-body systems but face difficulties in accessing excited states and in treating sign problems. We present a continuous-time path-integral Monte Carlo method for computing the low-lying spectrum of generic
quantum Hamiltonians within a projection subspace. The method projects the thermal density
matrix onto a subspace spanned by a chosen set of linearly independent states. It is free of Trotter discretization errors and systematically converges to the low-energy states which have finite overlap with the projection subspace as the $\beta$ parameter increases. While most effective for systems without a sign problem, the method also yields information about low-energy spectra when sign problems are present. We illustrate the approach on two problems. For the sign-free case, we compute the first four low-energy levels in the scaling limit of the one-dimensional Ising model with both transverse and longitudinal fields, demonstrating the flow from the conformal limit to the massive $E_8$
quantum field theory. For the sign-problem case, we apply the method to the frustrated Shastry-Sutherland model and
benchmark it against exact diagonalization on small
lattices. We also present results for larger systems beyond the
lattice sizes accessible to exact diagonalization, while limited to small $\beta$ where sign problems occur. Our method provides a general route toward
quantum Monte Carlo spectroscopy for
lattice Hamiltonians.
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All authors Abhishek Karna, Hansen S. Wu, Shailesh Chandrasekharan, Ribhu K. Kaul
Superconductivity
YBa$_2$Cu$_3$O$_7$ nano-constriction Josephson junctions and SQUIDs fabricated by focused helium-ion-beam irradiation
Christoph Schmid, Christopher Buckreus, David Haas et al. (+9 more)
By focused $30\,\mathrm{keV}$ He ion beam irradiation, epitaxially grown YBa$_2$Cu$_3$O$_7$ (YBCO) thin films can be driven from the superconducting to the insulating state with increasing irradiation dose. A properly chosen dose suppresses superconductivity down to $4\,\mathrm{K}$, while crystallinity is still preserved. With this approach we create areas of normal-conducting YBCO that can be used to define resistively shunted constriction-type Josephson junctions (cJJs) on the nanometer scale. We also demonstrate that the fabricated cJJs can be incorporated in direct current superconducting
quantum interference devices and can be used as detector junctions in THz
antennas.
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All authors Christoph Schmid, Christopher Buckreus, David Haas, Max Pröpper, Robin Hutt, César Magén, Dominik Hanisch, Max Karrer, Meinhard Schilling, Dieter Koelle, Reinhold Kleiner, Edward Goldobin
Strongly Correlated Electrons
Nodal structure of bound-state wave functions for systems with quartic dispersion
E.V. Gorbar, B.E. Grinyuk and V.P. Gusynin
The nodal structure of bound-state wave functions for one-dimensional
quantum systems with quartic energy-momentum dispersion and
polynomial potentials is analysed by using the semiclassical approximation and variational approach. For energies of bound states, we derive the quantization condition, obtained by using the complex Wentzel method, where we take into account perturbative (up to the fourth order) and nonperturbative in the Planck constant corrections. The bound-state energies and wave functions for the harmonic and quartic potentials are compared with those found by applying the variational approach utilizing the universal Gaussian basis. It is shown that the classical oscillation
theorem, valid for systems with quadratic energy-momentum dispersion, breaks down in the classically forbidden region where wave functions also have nodes, while it still remains valid in the classically allowed region. These results are confirmed in addition via the solutions of the exactly solvable problem of the fourth-order Schrodinger equation with a square well potential.
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Quantum Gases
Probing Bardeen-Cooper-Schrieffer pairing and quasiparticle formation in ultracold gases by Rydberg atom spectroscopy
Emilio Ramos Rodríguez, Marcel Gievers and Richard Schmidt
Locally probing pairing in fermionic superfluids, ranging from micro- to macroscopic scales, has been a long-standing challenge. Here, we investigate a new approach that uses Rydberg
impurities as a spectroscopic sensor of the surrounding strongly correlated state of ultracold paired
fermions. The extended wavefunction of the Rydberg electron induces a finite-range potential that can bind atoms from the BCS medium, forming molecular states. As a consequence, the optical absorption spectrum of the
impurity encodes key many-body properties. Using the functional determinant approach, we provide a direct measure of the superfluid gap through frequency shifts of dimer and trimer peaks. The spectra also reveal whether the Cooper pairs are broken or trapped intact. For static Rydberg atoms, we relate this signature of pairing to the suppression of the orthogonality catastrophe due to the superconducting gap resulting in the formation of well-defined polaron quasiparticles. Our work establishes Rydberg atom spectroscopy as a powerful local probe of strongly correlated matter.
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Materials Science
Effect of FABr Over-Stoichiometry on the Morphology and Optoelectronic Properties of Wide-Bandgap FAPbBr_3 Films
G. Ammirati, F. Martelli, F. Toschi et al. (+9 more)
In this study, we investigate the impact of formamidinium bromide (FABr) over-stoichiometry in the precursor solution on the optoelectronic properties and morphology of the resulting films of formamidinium lead bromide (FAPbBr_3). Optical characterization, including steady-state absorption, photoluminescence (PL), and femtosecond transient absorption spectroscopy, reveals a systematic blueshift in emission energy with increasing FABr content, attributed to the passivation of bromine vacancies and to the reduction of defect-assisted recombination. Power-dependent PL confirms this interpretation: the stoichiometric film exhibits a PL band due to donor-acceptor pair (DAP) recombination as identified by the typical excitation-dependent blueshift, whereas FABr-enriched samples show no evidence of DAP emission, indicating effective defect passivation. Additionally, morphological characterization shows a reduction in grain size with increasing FABr excess, indicating a trade-off between improved electronic quality and enhanced structural disorder. The film synthesized with a 5% excess of FABr provides the optimal balance, yielding the highest power conversion efficiency (6.26%), average visible transmittance (61.6%), and light utilization efficiency (3.85%). These results demonstrate that fine-tuning the precursor stoichiometry through controlled FABr addition represents a simple yet effective strategy to enhance the optoelectronic quality and performance of semitransparent perovskite
solar cells.
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All authors G. Ammirati, F. Martelli, F. Toschi, S. Turchini, P. O'Keeffe, A. Paladini, F. Matteocci, J. Barichello, D. Di Girolamo, S. Piccirillo, A. Di Carlo, D. Catone