Found 43 papers in cond-mat

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Quantum Tunneling Insights into the Atomic Landscapes of Graphite, Gold, and Silicon
Dhananjay Saikumar
arXiv:2402.10241v1 Announce Type: new Abstract: Scanning Tunneling Microscopy (STM) is a powerful technique that utilizes quantum tunneling to visualize atomic surfaces with high precision. This study presents detailed topographic maps and evaluates the local density of states (LDOS) for three distinct materials: Highly Oriented Pyrolytic Graphite (HOPG), gold, and silicon. By meticulously measuring the tunneling current from a finely pointed tip positioned nanometers above the sample, we successfully image the surface topography of HOPG, revealing a lattice constant of $0.28 \pm 0.01$ nm. Additionally, we determine the local work functions for gold and graphite to be $0.7 \pm 0.1$ eV and $0.5 \pm 0.1$ eV, respectively. Employing scanning tunneling spectroscopy, this work further investigates the LDOS for gold (a metal), graphite (a semi-metal), and silicon (a semiconductor), providing valuable insights into their electronic properties at the atomic level.

Standing spin waves in Permalloy-NiO bilayers as a probe of the interfacial exchange coupling
Diego Caso, Ana Garc\'ia-Prieto, Eugenia Sebastiani-Tofano, Akashdeep Kamra, Cayetano Hern\'andez, Pilar Prieto, Farkhad G. Aliev
arXiv:2402.10292v1 Announce Type: new Abstract: Ferromagnetic/Antiferromagnetic (FM/AFM) bilayers dynamics have been a recent topic of interest due to the interaction occurring at the interface, where the magnetic moments of the AFM can be imprinted into the FM, and the exchange bias field can affect these dynamics. Here, we investigate Permalloy (Py) and NiO (Py/NiO) hybrids and for comparison single Py films in the broad Py thickness range varied from few nm to 200 nm by using static (Kerr effect) and dynamic (spin waves) measurements along with micromagnetic simulations. We observe hybrid modes between uniform (ferromagnetic resonance FMR, n=0) and perpendicular standing spin waves (PSSWs, n=1, 2) and a clear enhancement of the PSSWs modes frequencies upon interfacing Py with NiO both from experiments and simulations. This enhancement becomes less pronounced as the thickness of the film increases, demonstrating its interfacial origin rooted in the exchange coupling between the FM and AFM layers. Besides, through micromagnetic simulations, we investigate and correlate changes in spatial profiles of the PSSWs with the interfacial exchange coupling. As the thickness is increased, we see that the n=1 and n=2 modes begin to couple with the fundamental FMR mode, resulting in asymmetric (with respect the Py layer center) modes. Our results suggest that PSSWs detection in a ferromagnet offers a means of probing the interfacial exchange coupling with the adjacent AFM layer. Furthermore, the controlled spatial symmetry breaking by the AFM layer enables engineering of PSSWs with different spatial profiles in the FM.

Athermal granular creep in a quenched sandpile
Nakul S. Deshpande, Paulo E. Arratia, Douglas J. Jerolmack
arXiv:2402.10338v1 Announce Type: new Abstract: Creep is a generic descriptor of slow motions -- in the context of materials, it describes quasi-static deformation of a solid when subjected to stresses below the global yield, at which all rigidity collapses and the material flows. Here, we experimentally investigate creep, flow, and the transition between the two states in a granular heap flow. Within the surface flowing layer the dimensionless strain rate diminishes with depth, there is an absence of spatial correlations, and there is no aging dynamics. Beneath this layer, the bulk creeps via localized avalanches of plasticity, and there is significant aging. The transition between fast surface flow and slow bulk creep and aging is observed to be in the vicinity of a critical inertial number of $I = 10^{-5}$. Surprisingly, at the cessation of surface flow and the `quenching' of the pile, creep persists in the absence of the flowing layer; albeit with significant differences for a pile that experiences a long duration of surface flow (strongly annealed) and one where flow during preparation does not last long (weakly annealed). Our results contribute to an emerging view of athermal granular creep, showing similarities across dry and submerged systems. Quenched quiescent heaps that creep indefinitely, however, present a challenge to granular rheology, and open new possibilities for interpreting and casting creep and deformation of soils in nature.

Orbital Competition in Bilayer Graphene's Fractional Quantum Hall Effect
Bishoy M. Kousa, Nemin Wei, Allan H. MacDonald
arXiv:2402.10440v1 Announce Type: new Abstract: The lowest Landau level of bilayer graphene has an octet of internal degrees of freedom, composed from spin, valley and orbital two-level systems. Dominance of $n=0$ orbitals over $n=1$ orbitals in low energy quantum fluctuations leads to distinct fractional quantum Hall characteristics compared dominance of $n=1$ over $n=0$. The competition between $n=0$ and $n=1$ orbitals depends sensitively on particle-hole asymmetry and on Lamb shifts due to exchange interactions with the negative energy sea, which must be accounted for simultaneously in assessing the orbital competition. We identify the circumstances under which $n=1$, which supports strong even-denominator FQH states with non-abelian quasiparticles, emerges robustly as the low-energy Landau level.

Electronic orders on the kagome lattice at the lower Van Hove filling
Yi-Qun Liu, Yan-Bin Liu, Wan-Sheng Wang, Da Wang, Qiang-Hua Wang
arXiv:2402.10455v1 Announce Type: new Abstract: We study the electronic orders at the lower van Hove filling in the kagome lattice. In the weak limit of the Hubbard interaction $U$ versus the hopping parameter $t$, we find that the system develops itinerant ferromagnetism; In the intermediate range of $U$, we find the system develops noncollinear magnetic order with orthogonal spin moments on nearest-neighbor bonds. This is in fact a Chern insulator supporting quantized anomalous Hall conductance; In the strong $U$ limit, we map the Hubbard model to the $t$-$J$ model with $J = 4t^2/U$. For moderate values of $J$ we recover the noncollinear magnetic order obtained in the Hubbard model. However, in the limit of $J\to 0$ (or $U\to \infty$) we find the ferromagnetic order revives. The results are obtained by combination of the random-phase approximation and functional renormalization group in the weak to moderate limit of $U$, and the variational quantum Monte Carlo for the $t$-$J$ model in the strong coupling limit. The phase diagram is distinctly different to that at the higher van Hove filling studied earlier, and the difference can be attributed to the lack of particle-hole symmetry in the band structure with respect to the Dirac point.

Electronic structure-property relationship in an Al0.5TiZrPdCuNi high-entropy alloy
Emil Babi\'c, Ignacio A. Figueroa, Vesna Mik\v{s}i\'c Trontl, Petar Pervan, Ivo Pletikosi\'c, Ramir Risti\'c, Amra Sal\v{c}inovi\'c Feti\'c, \v{Z}eljko Skoko, Damir Stare\v{s}ini\'c, Tonica Valla, Kre\v{s}o Zadro
arXiv:2402.10490v1 Announce Type: new Abstract: The valence band (VB) structure of an Al0.5TiZrPdCuNi high-entropy alloy (HEA) obtained from X-ray photoelectron spectroscopy has been compared to that recently calculated by Odbadrakh et al, 2019. Both experimental and theoretical VBs show split-band structures typical of alloys composed from the early (TE) and late (TL) transition metals. Accordingly, several properties of this alloy (both in the glassy and crystalline state) associated with the electronic structure (ES), are compared with those of similar TE-TL alloys. The comparison shows in addition to the usual dependence on the total TL content strong effect of alloying with Al on the density of states at the Fermi level, N(EF) and on the magnetic susceptibility of Al0.5TiZrPdCuNi HEA, which is like that of conventional glassy alloys, such as Zr-Cu-Al ones. Despite some similarity between the shapes of theoretical and corresponding experimental VBs there are significant quantitative differences between them which should be taken into account in any future studies of ES in HEAs and other compositionally complex alloys (CCA).

Moving and fusion of Majorana zero modes in the presence of nonadiabatic transitions
Qiongyao Wang, Jing Bai, Luting Xu, Wei Feng, Xin-Qi Li
arXiv:2402.10495v1 Announce Type: new Abstract: We perform simulations for moving and non-Abelian fusion of Majorana zero modes in topological superconducting quantum wires. We display interesting behaviors of nonadiabatic transition associated with the moving through mini-gate-controlled multiple-segments modulations. Owing to breaking of the initial fermion parity induced by nonadiabatic transitions, deviation from the standard fusion rule is analyzed. Moreover, we develop a measurement scheme to infer the amount of fermion parity breaking and nonadiabatic transition probability to excited states, based on the characteristic spectrum of measurement current by a uantum-point-contact detector, in measuring the charge occupation dynamics in a fusion-outcome-probing quantum dot.

Multiple localized-itinerant dualities in magnetism of 5f electron systems. The case of UPt$_2$Si$_2$
L. M. Sandratskii, V. M. Silkin, L. Havela
arXiv:2402.10507v1 Announce Type: new Abstract: The paper deals with the U based compound UPt$_2$Si$_2$ (UPS). The material was first treated as a localized 5f-electron system. Later, an opposite opinion of a predominantly itinerant nature of the system was put forward. The most recent publications treat UPS as a dual material. We suggest a material specific theoretical model based on the density functional theory plus Hubbard $U$ (DFT+$U$) calculations that describes the set of fundamental ground-state properties and high magnetic field experiment. The ground state properties include antiferromagnetic magnetic structure, magnetic easy axis, and the value of the U atomic moment. The in-field experiment shows the presence of a strong metamagnetic transition for the field parallel to the easy axis in contrast to the hard field direction where such a feature is absent. On the other hand, comparable induced magnetization values are obtained for both easy and hard field directions. Within the framework of the suggested model we show that the compound possesses well-formed atomic moments built by electrons treated as delocalized. To understand the experimental high-field properties we estimate exchange energy, magnetic anisotropy energy, and Zeeman energy. All three energies are shown to have comparable values what is crucial for the interpretation of the experiment. At all steps of the study we devote special attention to revealing and emphasizing the dual itinerant-localized properties of the material. The obtained forms of the duality are different: well defined atomic moments formed by the itinerant electrons, interplay of the single-site and two-site anisotropies, strong localization of two of the 5f electrons in contrast to the itinerant nature of the 5f electrons contributing to the states around the Fermi level.

Flat-band engineering of quasi-one-dimensional systems via supersymmetric transformations
Vit Jakubsky, Kevin Zelaya
arXiv:2402.10514v1 Announce Type: new Abstract: We introduce a systematic method to spectrally design quasi-one-dimensional crystal models described by the Dirac equation in the low-energy regime. The method is based on the supersymmetric transformation applied to an initially known pseudo-spin-1/2 model. This allows extending the corresponding susy partner so that the new model describes a pseudo-spin-1 system. The spectral design allows the introduction of a flat-band and discrete energies at will into the new model. The results are illustrated in two examples where the Su-Schriefer-Heeger chain is locally converted into a stub lattice.

Nonlinear optics driven magnetism reorientation in semiconductors
Qianqian Xue, Yan Sun, Jian Zhou
arXiv:2402.10518v1 Announce Type: new Abstract: Based on nonlinear optics, we develop a band theory to elucidate how light could manipulate magnetization, which is rooted by the quantum geometric structure and topological nature of electronic wavefunctions. Their existence are determined by the light polarization and specific material symmetry, based on the magnetic group theory. In general, both circularly and linearly polarized light could exert an effective magnetic field and torque effect, to reorient the magnetization. They are contributed by spin and orbital angular momenta simultaneously. Aided by group theory and first-principles calculations, we illustrate this theory using a showcase example of monolayer NiCl2, showing that light irradiation effectively generates an out-of-plane effective magnetic torque, which lifts its in-plane easy magnetization. According to magnetic dynamic simulations, the in-plane magnetization could be switched to the out-of-plane direction in a few nanoseconds under a modest light intensity, demonstrating its ultrafast nature desirable for quantum manipulation.

The Elusive member of the Ti-Al-C MAX family- Ti4AlC3
Subhajit Sarkar, Pratim Banerjee, Molly De Raychaudhury
arXiv:2402.10621v1 Announce Type: new Abstract: We report here perhaps the first successful synthesis and structural characterization of the n=3 family member of Tin+1AlCn, i. e. Ti4AlC3. X-ray Powder diffraction (XRD) data shows characteristic reflections of from corresponding to reflections from the (002), (004), (006), (008), (100), (102), (104), (0010), (105), (106), (0012), (1011) and (1012) planes at 2{\theta} =7.640, 15.170, 22.760, 30.50, 350, 37.40 38.30, 39.20, 41.30, 46.220, 55.240, 58.620 and 60.780 (double structure) respectively. Rietveld refinement of the XRD data reveals a phase purity of about 79 % for alpha-Ti4AlC3, 15 % for beta-Ti4AlC3 and the rest mostly that of cubic TiC (6 %). The primary crystal symmetry of the two dominant phases is the hexagonal P63/mmc. The precursors chosen were TiH2, Al metal powder and Carbon powder in a molar ratio of 3:1.2:2, which build the case for an Al-deficient condition. We adopted the pressureless sintering technique at 13500 C with a dwelling time of 4 hours under ultra-high vacuum of 10-7 mbar. The co-existence of trace amount of Ti2AlC at 1350 deg C is proven by the small structure at 2{\theta}=13.130. No trace of oxides like Al2O3 or TiO2 was found in the end product. The line profile width of XRD data indicates average grain size of the order of micro meter. The Scanning Electron Microscopy images show highly lamellar stacked growth of almost a pure MAX (alpha or beta) phase and grain size of micron order, agreeing well with the XRD data.

X-ray Linear Dichroic Tomography of Crystallographic and Topological Defects
Andreas Apseros, Valerio Scagnoli, Mirko Holler, Manuel Guizar-Sicairos, Zirui Gao, Christian Appel, Laura J. Heyderman, Claire Donnelly, Johannes Ihli
arXiv:2402.10647v1 Announce Type: new Abstract: The functionality of materials is determined by their composition and microstructure, that is, the distribution and orientation of crystalline grains, grain boundaries and the defects within them. The characterisation of the material's microstructure is therefore critical for materials applications such as catalysis, energy storage and buildings. Until now, characterization techniques that map the distribution of grains, their orientation, and the presence of defects have either been limited to surface investigations, to spatial resolutions of a few hundred nanometres, or to systems of thickness around one hundred nanometres, thus requiring destructive sample preparation for measurements and preventing the study of system-representative volumes or the investigation of materials under operational conditions. Here, we present X-ray linear dichroic orientation tomography, a quantitative, non-invasive technique that allows for an intra- and inter-granular characterisation of extended polycrystalline and amorphous materials in three dimensions (3D). We present the detailed characterisation of a polycrystalline sample of vanadium pentoxide (V2O5), a key catalyst in the production of sulfuric acid. In addition to determining the nanoscale composition, we map the crystal orientation throughout the polycrystalline sample with 73 nm spatial resolution. We identify grains, as well as twist, tilt, and twin grain boundaries. We further observe the creation and annihilation of topological defects promoted by the presence of volume crystallographic defects in 3D. Our method's non-destructive and spectroscopic nature opens the door to in-operando combined chemical and microstructural investigations of functional materials, including energy and mechanical materials in existing industries, as well as quantum materials for future technologies.

Human-machine collaboration: ordering mechanism of rank$-2$ spin liquid on breathing pyrochlore lattice
Nicolas Sadoune, Ke Liu, Han Yan, Ludovic D. C. Jaubert, Nic Shannon, Lode Pollet
arXiv:2402.10658v1 Announce Type: new Abstract: Machine learning algorithms thrive on large data sets of good quality. Here we show that they can also excel in a typical research setting with little data of limited quality, through an interplay of insights coming from machine, and human researchers. The question we address is the unsolved problem of ordering out of a spin-liquid phase described by an emergent rank-2 $U(1)$ gauge theory, as described by [H. Yan it et al., Phys. Rev. Lett. 124, 127203 (2020)]. Published Monte Carlo simulations for this problem are consistent with a strong first-order phase transition, out of the R2-U1 spin liquid, but were too noisy for the form of low-temperature order to be identified. Using a highly-interpretable machine learning approach based on a support vector machine with a tensorial kernel (TKSVM), we re-analyze this Monte Carlo data, gaining new information about the form of order that could in turn be interpreted by traditionally-trained physicists. We find that the low-temperature ordered phase is a form of hybrid nematic order with emergent $Z_2$ symmetry, which allows for a sub-extensive set of domain walls at zero energy. This complex form of order arises due to a subtle thermal order-by-disorder mechanism, that can be understood from the fluctuations of the tensor electric field of the parent rank-2 gauge theory. These results were obtained by a back-and-forth process which closely resembles a collaboration between human researchers and machines. We argue that this "collaborative" approach may provide a blueprint for solving other problems that have not yielded to human insights alone.

Fractional Spin Quantum Hall Effect in Weakly Coupled Spin Chain Arrays
Even Thingstad, Pierre Fromholz, Flavio Ronetti, Daniel Loss, Jelena Klinovaja
arXiv:2402.10849v1 Announce Type: new Abstract: Topological magnetic insulators host chiral gapless edge modes. In the presence of strong interaction effects, the spin of these modes may fractionalize. Studying a 2D array of coupled insulating spin-1/2 chains, we show how spatially modulated magnetic fields and Dzyaloshinskii-Moriya interactions can be exploited to realize chiral spin liquids or integer and fractional spin quantum Hall effect phases. These are characterized by a gapped bulk spectrum and gapless chiral edge modes with fractional spin. The spin fractionalization is manifested in the quantized spin conductance, which can be used to probe the fractional spin quantum Hall effect. We analyze the system via bosonization and perturbative renormalization group techniques that allow us to identify the most relevant terms induced by the spin-spin interactions that open gaps and render the system topological under well-specified resonance conditions. We show explicitly that the emerging phase is a genuine chiral spin liquid. We suggest that the phases can be realized experimentally in synthetic spin chains and ultracold atom systems.

Design of 2D Skyrmionic Metamaterial Through Controlled Assembly
Qichen Xu, Zhuanglin Shen, Alexander Edstr\"om, I. P. Miranda, Zhiwei Lu, Anders Bergman, Danny Thonig, Wanjian Yin, Olle Eriksson, Anna Delin
arXiv:2402.10874v1 Announce Type: new Abstract: Despite extensive research on magnetic skyrmions and antiskyrmions, a significant challenge remains in crafting nontrivial high-order skyrmionic textures with varying, or even tailor-made, topologies. We address this challenge, by focusing on a construction pathway of skyrmionics metamaterial within a monolayer thin film and suggest several promising lattice-like, flakes-like, and cell-like skyrmionic metamaterials that are surprisingly stable. Central to our approach is the concept of 'simulated controlled assembly', in short, a protocol inspired by 'click chemistry' that allows for positioning topological magnetic structures where one likes, and then allowing for energy minimization to elucidate the stability. Utilizing high-throughput atomistic-spin-dynamic (ASD) simulations alongside state-of-the-art AI-driven tools, we have isolated skyrmions (topological charge Q=1), antiskyrmions (Q=-1), and skyrmionium (Q=0). These entities serve as foundational 'skyrmionic building blocks' to forming reported intricate textures. In this work, two key contributions are introduced to the field of skyrmionic systems. First, we present a novel method for integrating control assembly protocols for the stabilization and investigation of topological magnets, which marks a significant advancement in the ability to explore new skyrmionic textures. Second, we report on the discovery of skyrmionic metamaterials, which shows a plethora of complex topologies that are possible to investigate theoretically and experimentally.

Classifying topology in photonic crystal slabs with radiative environments
Stephan Wong, Terry A. Loring, Alexander Cerjan
arXiv:2402.10347v1 Announce Type: cross Abstract: In the recent years, photonic Chern materials have attracted substantial interest as they feature topological edge states that are robust against disorder, promising to realize defect-agnostic integrated photonic crystal slab devices. However, the out-of-plane radiative losses in those photonic Chern slabs has been previously neglected, yielding limited accuracy for predictions of these systems' topological protection. Here, we develop a general framework for measuring the topological protection in photonic systems, such as in photonic crystal slabs, while accounting for in-plane and out-of-plane radiative losses. Our approach relies on the spectral localizer that combines the position and Hamiltonian matrices of the system to draw a real-picture of the system's topology. This operator-based approach to topology allows us to use an effective Hamiltonian directly derived from the full-wave Maxwell equations after discretization via finite-elements method (FEM), resulting in the full account of all the system's physical processes. As the spectral FEM-localizer is constructed solely from FEM discretization of the system's master equation, the proposed framework is applicable to any physical system and is compatible with commonly used FEM software. Moving forward, we anticipate the generality of the method to aid in the topological classification of a broad range of complex physical systems.

Quantum dimer models with Rydberg gadgets
Zhongda Zeng, Giuliano Giudici, Hannes Pichler
arXiv:2402.10651v1 Announce Type: cross Abstract: The Rydberg blockade mechanism is an important ingredient in quantum simulators based on neutral atom arrays. It enables the emergence of a rich variety of quantum phases of matter, such as topological spin liquids. The typically isotropic nature of the blockade effect, however, restricts the range of natively accessible models and quantum states. In this work, we propose a method to systematically overcome this limitation, by developing gadgets, i.e., specific arrangements of atoms, that transform the underlying Rydberg blockade into more general constraints. We apply this technique to realize dimer models on square and triangular geometries. In these setups, we study the role of the quantum fluctuations induced by a coherent drive of the atoms and find signatures of $U(1)$ and $\mathbb{Z}_2$ quantum spin liquid states in the respective ground states. Finally, we show that these states can be dynamically prepared with high fidelity, paving the way for the quantum simulation of a broader class of constrained models and topological matter in experiments with Rydberg atom arrays.

Lattice realization of complex CFTs: Two-dimensional Potts model with $Q>4$ states
Jesper Lykke Jacobsen, Kay Joerg Wiese
arXiv:2402.10732v1 Announce Type: cross Abstract: The two-dimensional $Q$-state Potts model with real couplings has a first-order transition for $Q>4$. We study a loop-model realization in which $Q$ is a continuous parameter. This model allows for the collision of a critical and a tricritical fixed point at $Q=4$, which then emerge as complex conformally invariant theories at $Q>4$, or even complex $Q$, for suitable complex coupling constants. All critical exponents can be obtained as analytic continuation of known exact results for $Q \le 4$. We verify this scenario in detail for $Q=5$ using transfer-matrix computations.

Weak Ergodicity Breaking in Optical Sensing
V. G. Ramesh, S. R. K. Rodriguez
arXiv:2402.10791v1 Announce Type: cross Abstract: The time-integrated intensity transmitted by a laser driven resonator obeys L\'evy's arcsine laws [Ramesh \textit{et al.}, Phys. Rev. Lett. \textit{in press} (2024)]. Here we demonstrate the implications of these laws for optical sensing. We consider the standard goal of resonant optical sensors, namely to report a perturbation to their resonance frequency. In this context, we quantify the sensing precision attained using a finite energy budget combined with time or ensemble averaging of the time-integrated intensity. We find that ensemble averaging outperforms time averaging for short measurement times, but the advantage disappears as the measurement time increases. We explain this behavior in terms of weak ergodicity breaking, arising when the time for the time-integrated intensity to explore the entire phase space diverges but the measurement time remains finite. Evidence that the former time diverges is presented in first passage and return time distributions. Our results are relevant to all types of sensors, in optics and beyond, where stochastic time-integrated fields or intensities are measured to detect an event. In particular, choosing the right averaging strategy can improve sensing precision by orders of magnitude with zero energy cost.

Observation of the two-photon Landau-Zener-St\"uckelberg-Majorana effect
Isak Bj\"orkman, Marko Kuzmanovi\'c, Gheorghe Sorin Paraoanu
arXiv:2402.10833v1 Announce Type: cross Abstract: Second-order processes introduce nonlinearities in quantum dynamics, unlocking a totally unexpected area of control operations. Here we show that the well-known Landau-Zener-St\"uckelberg-Majorana (LZSM) transition can be driven by a virtual process in a three-level system whereby two photons from a drive with linearly-modulated phase create excitations onto the third level while avoiding completely the first level. We implement this experimentally in a transmon qubit achieving a population transfer of $98\%$, limited by relaxation. We predict and observe experimentally the doubling of the LZSM velocity. The observation of this effect is made possible by the nearly-exact cancellation of the two-photon ac Stark shift when the third transition is included. Furthermore, we demonstrate considerable robustness to offsets in frequency and amplitude, both in theory and experimentally.

Fast counter-diabatic Thouless pumping in the Rice-Mele mode
Joshua Chiel, Christopher Jarzynski, Jay Sau
arXiv:2402.10872v1 Announce Type: cross Abstract: Thouless pumping is a transport phenomenon where a periodically varying Hamiltonian can transfer a quantized amount of charge when the time-dependence of the Hamiltonian is quasi-adiabatic. Past proposals to speed up this process involving Floquet techniques lead to a subtle problem of setting the initial state of the system. In this work we apply counter-diabatic driving to the Rice-Mele model, which is one of the simplest models for Thouless pumping, to ensure that the system remains in the ground state for any driving speed. We show that the pumped charge across each bond of the Rice-Mele model is given by a topologically quantized Chern number in this case. However, the counter-diabatic driving in a general case turns out to involve long-range hopping. We show that this can be mitigated either by choosing a very specific example of the Rice-Mele model or by numerical optimization of the Hamiltonian to create experimentally realizable variants of fast pumping in the Rice-Mele model.

Single-photon emitters in WSe$_2$: The critical role of phonons on excitation schemes and indistinguishability
Luca Vannucci, Jos\'e Ferreira Neto, Claudia Piccinini, Athanasios Paralikis, Niels Gregersen, Battulga Munkhbat
arXiv:2402.10897v1 Announce Type: cross Abstract: Within optical quantum information processing, single-photon sources based on a two-level system in a semiconductor material allow for on-demand generation of single photons. To initiate the spontaneous emission process, it is necessary to efficiently populate the excited state. However, reconciling the requirement for on-demand excitation with both high efficiency and high photon indistinguishability remains a challenge due to the presence of charge noise and phonon-induced decoherence in the solid-state environment. Here, we propose a method for reconstructing the phonon spectral density experienced by WSe$_{2}$ quantum emitters in the emission process. Using the reconstructed phonon spectral density, we analyze the performance of the resonant, phonon-assisted, and SUPER swing-up excitation schemes. Under resonant excitation, we obtain an exciton preparation fidelity limited to $\sim$0.80 by the strong phonon coupling, which improves to 0.96 for the SUPER scheme (or 0.89, depending on the type of emitter considered). Under near-resonant phonon-assisted excitation, we observe near-unity excitation fidelity up to 0.976 (0.997). Additionally, we demonstrate that, assuming the suppression of the phonon sidebands, residual dephasing mechanisms such as charge/spin fluctuations are the dominating decoherence mechanisms undermining the photon indistinguishability.

Intrinsic in-plane magnetononlinear Hall effect in tilted Weyl semimetals
Longjun Xiang, Jian Wang
arXiv:2209.03527v4 Announce Type: replace Abstract: Armed with the extended semiclassical theory, we propose a Hall effect at $EB$ order, particularly in Weyl semimetals (WSMs). We dub this effect the in-plane magnetononlinear Hall effect (IMHE) since the Hall current and the driving electric and magnetic fields are confined in the same plane. Similar to the intrinsic anomalous Hall effect, the IMHE features an intrinsic nature because it arises from the field-induced anomalous velocity $\vec{E} \times \vec{\Omega}^B$, where $\vec{\Omega}^B$ is the Berry curvature induced by the magnetic field through both minimal and Zeeman couplings. Employing the low-energy effective Hamiltonian of WSMs, we reveal that the tilt of the Weyl cone is the key to triggering this effect. Notably, we find that the IMHE can survive even when the \textit{chiral anomaly} disappears because $\vect{\Omega}^B$ (as the correction of the conventional Berry curvature) does not contribute to the monopole charge. Furthermore, we elucidate the interplay between minimal and Zeeman couplings for this effect. Finally, the experimental strategy to detect the IMHE is discussed.

Time-dependent properties of run-and-tumble particles: Density relaxation
Tanmoy Chakraborty, Punyabrata Pradhan
arXiv:2209.11995v4 Announce Type: replace Abstract: We characterize collective diffusion of hardcore run-and-tumble particles (RTPs) by explicitly calculating the bulk-diffusion coefficient $D(\rho, \gamma)$ in two minimal models on a $d$ dimensional periodic lattice for arbitrary density $\rho$ and tumbling rate $\gamma$. We focus on two models: Model I is the standard version of hardcore RTPs [Phys. Rev. E \textbf{89}, 012706 (2014)], whereas model II is a long-ranged lattice gas (LLG) with hardcore exclusion - an analytically tractable variant of model I; notably, both models are found to have qualitatively similar features. In the strong-persistence limit $\gamma \rightarrow 0$ (i.e., dimensionless $r_0 \gamma /v \rightarrow 0$), with $v$ and $r_{0}$ being the self-propulsion speed and particle diameter, respectively, the fascinating interplay between persistence and interaction is quantified in terms of two length scales - mean gap, or "mean free path", and persistence length $l_{p}=v/ \gamma$. Indeed, for a small tumbling rate, the bulk-diffusion coefficient varies as a power law in a wide range of density: $D \propto \rho^{-\alpha}$, with exponent $\alpha$ gradually crossing over from $\alpha = 2$ at high densities to $\alpha = 0$ at low densities. Thus, the density relaxation is governed by a nonlinear diffusion equation with anomalous spatiotemporal scaling. Moreover, in the thermodynamic limit, we show that the bulk-diffusion coefficient - for $\rho,\gamma \rightarrow 0$ with $\rho/\gamma$ fixed - has a scaling form $D(\rho, \gamma) = D^{(0)}\mathcal{F}(\psi=\rho a v/\gamma)$, where $a\sim r_{0}^{d-1}$ is particle cross-section and $D^{(0)}$ is proportional to the diffusivity of noninteracting particles; the scaling function $\mathcal{F}(\psi)$ is calculated analytically for model I and numerically for model II. Our arguments are independent of dimensions and microscopic details.

Field-induced hybridization of moir\'e excitons in MoSe$_2$/WS$_2$ heterobilayers
Borislav Polovnikov, Johannes Scherzer, Subhradeep Misra, Xin Huang, Christian Mohl, Zhijie Li, Jonas G\"oser, Jonathan F\"orste, Ismail Bilgin, Kenji Watanabe, Takashi Taniguchi, Alexander H\"ogele, Anvar S. Baimuratov
arXiv:2304.14037v2 Announce Type: replace Abstract: We study experimentally and theoretically the hybridization among intralayer and interlayer moir\'e excitons in a MoSe$_2$/WS$_2$ heterostructure with antiparallel alignment. Using a dual-gate device and cryogenic white light reflectance and narrow-band laser modulation spectroscopy, we subject the moir\'e excitons in the MoSe$_2$/WS$_2$ heterostack to a perpendicular electric field, monitor the field-induced dispersion and hybridization of intralayer and interlayer moir\'e exciton states, and induce a cross-over from type I to type II band alignment. Moreover, we employ perpendicular magnetic fields to map out the dependence of the corresponding exciton Land\'e $g$-factors on the electric field. Finally, we develop an effective theoretical model combining resonant and non-resonant contributions to moir\'e potentials to explain the observed phenomenology, and highlight the relevance of interlayer coupling for structures with close energetic band alignment as in MoSe$_2$/WS$_2$.

Lieb-Schultz-Mattis Theorem in Open Quantum Systems
Kohei Kawabata, Ramanjit Sohal, Shinsei Ryu
arXiv:2305.16496v2 Announce Type: replace Abstract: The Lieb-Schultz-Mattis (LSM) theorem provides a general constraint on quantum many-body systems and plays a significant role in the Haldane gap phenomena and topological phases of matter. Here, we extend the LSM theorem to open quantum systems and establish a general theorem that restricts the steady state and spectral gap of Liouvillians based solely on symmetry. Specifically, we demonstrate that the unique gapped steady state is prohibited when translation invariance and U (1) symmetry are simultaneously present for noninteger filling numbers. As an illustrative example, we find that no dissipative gap is open in the spin-1/2 dissipative Heisenberg model while a dissipative gap can be open in the spin-1 counterpart -- an analog of the Haldane gap phenomena in open quantum systems. Furthermore, we show that the LSM constraint manifests itself in a quantum anomaly of the dissipative form factor of Liouvillians. We also find the LSM constraints due to symmetry intrinsic to open quantum systems, such as Kubo-Martin-Schwinger symmetry. Our work leads to a unified understanding of phases and phenomena in open quantum systems.

Moir\'e fractals in twisted graphene layers
Deepanshu AggarwalIIT Delhi, Rohit NarulaIIT Delhi, Sankalpa GhoshIIT Delhi
arXiv:2306.04580v3 Announce Type: replace Abstract: Twisted bilayer graphene (TBLG) subject to a sequence of commensurate external periodic potentials reveals the formation of moir\'{e} fractals (MF) that share striking similarities with the central place theory (CPT) of economic geography, thus uncovering a remarkable connection between twistronics and the geometry of economic zones. MFs arise from the self-similarity of the emergent hierarchy of Brillouin zones (BZ), forming a nested subband structure within the bandwidth of the original moir\'{e} bands. We derive the fractal generators (FG) for TBLG under these external potentials and explore their impact on the hierarchy of the BZ edges and the wavefunctions at the Dirac point. By examining realistic super-moir\'{e} structures (SMS) and demonstrating their equivalence to MFs with periodic perturbations under specific conditions, we establish MFs as a general description for such systems. Furthermore, we uncover parallels between the modification of the BZ hierarchy and magnetic BZ formation in Hofstadter's butterfly (HB), allowing us to construct an incommensurability measure for MFs \textit{vs.} twist angle. The resulting bandstructure hierarchy bolsters correlation effects, pushing more bands within the same energy window for both commensurate and incommensurate TBLG.

Coexistence of symmetry-protected topological order and Neel order in the spin-1/2 ladder antiferromagnet C9H18N2CuBr4
Tao Hong, Imam Makhfudz, Xianglin Ke, Andrew F. May, Andrey A. Podlesnyak, Daniel Pajerowski, Barry Winn, Merce Deumal, Yasumasa Takano, Mark M. Turnbull
arXiv:2306.06021v3 Announce Type: replace Abstract: Topological phases of matter are beyond the paradigm of Landau's symmetry breaking and have challenged our understanding of condensed matter systems. Here we report a new type of symmetry-protected topological phase of matter in the spin-1/2 coupled two-leg ladder antiferromagnet C9H18N2CuBr4, DLCB for short. In this two-sublattice antiferromagnet with a weak easy-axis anisotropy, we find no evidence of a conventional spin-flop transition in the magnetization with the magnetic field applied parallel to the easy axis at T=0.4 K, well below TN=2.0 K. Moreover, the temperature dependence of the gapped transverse excitations across TN indicates that they are not the conventional S=1 magnons associated with explicit symmetry breaking. Instead, the thermal renormalization of the gap energy shows a remarkable agreement with a calculation for the three-dimensional O(3) nonlinear sigma model. Accordingly, the spin gap in DLCB is not due to the spin anisotropy but to the separation between a spin singlet state and a triplet excited state. Since an antiferromagnetic spin-1/2 ladder systems can be mapped onto the spin-1 chain, the notion of the Haldane gap is proposed to explain the opening of the spin gap in DLCB. Therefore, the ground state of DLCB is best described as a quantum superposition of a Haldane phase and a Neel-ordered phase, which resembles the quantum state of a qubit in quantum computing. Our results indicate the presence of a symmetry-protected topological order coexisting with an antiferromagnetic order in this material.

Pumping with Symmetry
Julio Andr\'es Iglesias Mart\'inez, Muamer Kadic, Vincent Laude, Emil Prodan
arXiv:2306.16401v3 Announce Type: replace Abstract: Re-configurable materials and meta-materials can jump between space symmetry classes during their deformations. Here, we introduce the concept of singular symmetry enhancement, which refers to an abrupt jump to a higher symmetry class accompanied by an un-avoidable reduction in the number of dispersion bands of the excitations of the material. Such phenomenon prompts closings of some of the spectral resonant gaps along singular manifolds in a parameter space. In this work, we demonstrate that these singular manifolds can carry topological charges. As a concrete example, we show that a deformation of an acoustic crystal that encircles a p11g-symmetric configuration of an array of cavity resonators results in an adiabatic cycle that carries a Chern number in the bulk and displays Thouless pumping at the edges. This points to a very general guiding principle for recognizing cyclic adiabatic processes with high potential for topological pumping in complex materials and meta-materials, which rests entirely on symmetry arguments.

Defect-Induced Low-Energy Majorana Excitations in the Kitaev Magnet $\alpha$-RuCl$_3$
K. Imamura, Y. Mizukami, O. Tanaka, R. Grasset, M. Konczykowski, N. Kurita, H. Tanaka, Y. Matsuda, M. G. Yamada, K. Hashimoto, T. Shibauchi
arXiv:2306.17380v2 Announce Type: replace Abstract: The excitations in the Kitaev spin liquid (KSL) can be described by Majorana fermions, which have characteristic field dependence of bulk gap and topological edge modes. In the high-field state of layered honeycomb magnet $\alpha$-RuCl$_3$, experimental results supporting these Majorana features have been reported recently. However, there are challenges due to sample dependence and the impact of inevitable disorder on the KSL is poorly understood. Here we study how low-energy excitations are modified by introducing point defects in $\alpha$-RuCl$_3$ using electron irradiation, which induces site vacancies and exchange randomness. High-resolution measurements of the temperature dependence of specific heat $C(T)$ under in-plane fields $H$ reveal that while the field-dependent Majorana gap is almost intact, additional low-energy states with $C/T=A(H)T$ are induced by introduced defects. At low temperatures, we obtain the data collapse of $C/T\sim H^{-\gamma}(T/H)$ expected for a disordered quantum spin system, but with an anomalously large exponent $\gamma$. This leads us to find a power-law relationship between the coefficient $A(H)$ and the field-sensitive Majorana gap. These results are consistent with the picture that the disorder induces low-energy linear Majorana excitations, which may be considered as a weak localization effect of Majorana fermions in the KSL.

Edge Theories for Anyon Condensation Phase Transitions
David M. Long, Andrew C. Doherty
arXiv:2307.12509v4 Announce Type: replace Abstract: The algebraic tools used to study topological phases of matter are not clearly suited to studying processes in which the bulk energy gap closes, such as phase transitions. We describe an elementary two edge thought experiment which reveals the effect of an anyon condensation phase transition on the robust edge properties of a sample, bypassing a limitation of the algebraic description. In particular, the two edge construction allows some edge degrees of freedom to be tracked through the transition, despite the bulk gap closing. The two edge model demonstrates that bulk anyon condensation induces symmetry breaking in the edge model. Further, the construction recovers the expected result that the number of chiral current carrying modes at the edge cannot change through anyon condensation. We illustrate the construction through detailed analysis of anyon condensation transitions in an achiral phase, the toric code, and in chiral phases, the Kitaev spin liquids.

Phase transitions out of quantum Hall states in moir\'e TMD bilayers
Xue-Yang Song, Ya-Hui Zhang, T. Senthil
arXiv:2308.10903v3 Announce Type: replace Abstract: Motivated by the recent experimental breakthroughs in observing Fractional Quantum Anomalous Hall (FQAH) states in moir\'e materials, we propose and study various unconventional phase transitions between quantum Hall phases and Fermi liquids or charge ordered phases upon tuning the bandwidth. At a fixed rational lattice filling $\nu$, we describe a quantum Ginzburg-Landau theory to describe the intertwinement between the FQAH and Charge Density Wave (CDW) orders. We use this theory to describe phase transitions between the FQAH and a CDW insulator. The critical theory for a direct second order transition resembles that of the familiar deconfined quantum critical point (DQCP) but with an additional Chern-Simons term. At filling -1/2, we study the possibility of a continuous transition between the composite Fermi liquid (CFL) and the Fermi liquid (FL) building on and refining previous work by Barkeshli and McGreevy. Crucially we show that filling constraints ignored in that work ensure that translation symmetry alone is enough to enable a second order CFL-FL transition. We argue that there must be critical CDW fluctuations though neither phase has long range CDW order. We present experimental signatures the most striking of which is a universal jump of both longitudinal and Hall resistivities at the critical point. With disorder, we argue that the CDW order gets pinned and the CFL-FL evolution happens through an intermediate electrically insulating phase with mobile neutral fermions. A clean analog of this insulating phase with long range CDW order and a neutral fermi surface can potentially also exist. We also present a critical theory for the CFL to FL transition at filling -3/4. Our work opens up a new avenue to realize deconfined criticality and fractionalized phases beyond familiar Landau level physics in the moire Chern band system.

Topology of Bi$_2$Se$_3$ nanosheets
Lucas Maisel Licer\'an, Sebastiaan Koerhuis, Daniel Vanmaekelbergh, Henk Stoof
arXiv:2309.02792v4 Announce Type: replace Abstract: Recently, the quantum spin-Hall edge channels of two-dimensional colloidal nanocrystals of the topological insulator Bi$_2$Se$_3$ were observed directly. Motivated by this development, we reconsider the four-band effective model which has been traditionally employed in the past to describe thin nanosheets of this material. Derived from a three-dimensional $\boldsymbol{k} \boldsymbol{\cdot} \boldsymbol{p}$ model, it physically describes the top and bottom electronic surface states at the $\Gamma$ point that become gapped due to the material's small thickness. However, we find that the four-band model for the surface states alone, as derived directly from the three-dimensional theory, is inadequate for the description of thin films of a few quintuple layers and even yields an incorrect topological invariant within a significant range of thicknesses. To address this limitation we propose an eight-band model which, in addition to the surface states, also incorporates the set of bulk states closest to the Fermi level. We find that the eight-band model not only captures most of the experimental observations, but also agrees with previous first-principles calculations of the $\mathbb{Z}_{2}$ invariant in thin films of varying thickness. Moreover, we demonstrate that the topological properties of thin Bi$_2$Se$_3$ nanosheets emerge as a result of an interplay between bands of surface-like and bulk-like character. Specifically, contrary to the situation in the four-band model, the surface-like bands of the eight-band model are topologically nontrivial due to a band inversion enabled by the presence of the additional bulk-like bands.

High-field immiscibility of electrons belonging to adjacent twinned bismuth crystals
Yuhao Ye, Akiyoshi Yamada, Yuto Kinoshita, Jinhua Wang, Pan Nie, Liangcai Xu, Huakun Zuo, Masashi Tokunaga, Neil Harrison, Ross D. McDonald, Alexey V. Suslov, Arzhang Ardavan, Moon-Sun Nam, David LeBoeuf, Cyril Proust, Beno\^it Fauqu\'e, Yuki Fuseya, Zengwei Zhu, Kamran Behnia
arXiv:2310.06685v2 Announce Type: replace Abstract: Bulk bismuth has a complex Landau spectrum. The small effective masses and the large g-factors are anisotropic. The chemical potential drifts at high magnetic fields. Moreover, twin boundaries further complexify the interpretation of the data by producing extra anomalies in the extreme quantum limit. Here, we present a study of angle dependence of magnetoresistance up to 65 T in bismuth complemented with Nernst, ultrasound, and magneto-optic data. All observed anomalies can be explained in a single-particle picture of a sample consisting of two twinned crystals tilted by 108$^{\circ}$ and with two adjacent crystals keeping their own chemical potentials despite a shift between chemical potentials as large as 68 meV at 65 T. This implies an energy barrier between adjacent twinned crystals reminiscent of a metal-semiconductor Schottky barrier or a p-n junction. We argue that this barrier is built by accumulating charge carriers of opposite signs across a twin boundary.

Quantum phases of spin-1/2 extended XY model in transverse magnetic field
Rakesh Kumar Malakar, Asim Kumar Ghosh
arXiv:2310.11243v2 Announce Type: replace Abstract: In this study, a spin-1/2 extended anisotropic XY chain has been introduced in which both time reversal and SU(2) symmetries are broken but $Z_2$ symmetry is preserved. Magnetic and topological phase diagrams in the parameter space have been drawn in the presence of transverse magnetic field. Entanglement measures like mutual information and quantum discord are also evaluated and it indicates that these transitions are second order in nature. Quantum phase transition is noted at zero magnetic field, as well as magnetic long range order is found to withstand magnetic field of any strength. Exact analytic results for spin-spin correlation functions have been obtained in terms of Jordan Wigner fermionization. Existence of long range magnetic order has been investigated numerically by finding correlation functions as well as the Binder cumulant in the ground state. Dispersion relation, ground state energy, and energy gap are obtained analytically. In order to find the topologically nontrivial phase, sign of Pfaffian invariant and value of winding number have been evaluated. Both magnetic and topological phases are robust against the magnetic field and found to move coercively in the parameter space with the variation of its strength. Long range orders along two orthogonal directions and two different topological phases are found and their one-to-one correspondence has been found. Finally casting the spinless fermions onto Majorana fermions, properties of zero energy edge states are studied. Three different kinds of Majorana pairings are noted. In the trivial phase, next-nearest-neighbor Majorana pairing is found, whereas two different types of nearest-neighbor Majorana pairings are identified in the topological superconducting phase.

Nonadiabatic transitions during a passage near a critical point
Nikolai A. Sinitsyn, Vijay Ganesh Sadhasivam, Fumika Suzuki
arXiv:2312.10664v2 Announce Type: replace Abstract: The passage through a critical point of a many-body quantum system leads to abundant nonadiabatic excitations. Here, we explore a regime, in which the critical point is not crossed although the system is passing slowly very close to it. We show that the leading exponent for the excitation probability then can be obtained by standard arguments of the Dykhne formula but the exponential prefactor is no longer simple, and behaves as a power law on the characteristic transition rate. We derive this prefactor for the nonlinear Landau-Zener (nLZ) model by adjusting the Dykhne's approach. Then, we introduce an exactly solvable model of the transition near a critical point in the Stark ladder. We derive the number of the excitations for it without approximations, and find qualitatively similar results for the excitation scaling.

Untangling the valley structure of states for intravalley exchange anisotropy in lead chalcogenides quantum dots
I. D. Avdeev, M. O. Nestoklon
arXiv:2312.14918v2 Announce Type: replace Abstract: We put forward a generalized procedure which allows to restore the bulk-like electron and hole wave functions localized in certain valleys from the wave functions of quantum confined electron/hole states obtained in atomistic calculations of nanostructures. As a demonstration, the procedure is applied to the lead chalcogenide quantum dots to extract the effective intravalley Hamiltonian of the exchange interaction for the ground exciton state PbS and PbSe quantum dots. Renormalization of the anisotropic intravalley matrix elemets of velocity is also calculated. The results demonstrate that the matrix elements of intravalley exchange in PbS quantum dots are much more anisotropic than ones in PbSe.

A Hybrid Machine Learning Framework for Predicting Hydrogen Storage Capacities: Unsupervised Feature Learning with Deep Neural Networks
Satadeep Bhattacharjee, Pritam Das, Swetarekha Ram, Seung-Cheol Lee
arXiv:2401.17587v2 Announce Type: replace Abstract: In this study, we present a sophisticated hybrid machine-learning framework that significantly improves the accuracy of predicting hydrogen storage capacities in metal hydrides. This is a critical challenge due to the scarcity of experimental data and the complexity of high-dimensional feature spaces. Our approach employs the power of unsupervised learning through the use of a state-of-the-art autoencoder. This autoencoder is trained on elemental descriptors obtained from Mendeleev software, enabling the extraction of a meaningful and lower dimensional latent space from the input data. This latent representation serves as the basis for our deep multi-layer perceptron (MLP) model, which consists of five layers and shows good precision in predicting hydrogen storage capacities. Furthermore, our results show very good agreement with the results of density functional theory (DFT). In addition to addressing the limitations caused by limited and unevenly distributed data in the field of hydrogen storage materials, we also focus on discovering new materials that show promising opportunities for hydrogen storage. These materials were identified using both feature-based approaches and predictions generated by a large language model. Finally, our investigation into the effectiveness of transferring weights from the autoencoder to the MLP, in addition to the latent features, suggests that while this strategy slightly improves model performance indicated by a slightly higher R$^2$ value and lower RMSE, it emphasizes the intricate challenge of adapting pre-trained weights for specific supervised tasks.

Theory of biexciton-polaritons in transition metal dichalcogenide monolayers
Andrey Kudlis, Ivan A. Aleksandrov, Mikhail M. Glazov, Ivan A. Shelykh
arXiv:2402.09110v3 Announce Type: replace Abstract: We theoretically investigate a nonlinear optical response of a planar microcavity with an embedded transition metal dicalcogenide monolayer of a when an energy of a biexcitonic transition is brought in resonance with an energy of a cavity mode. We demonstrate that the emission spectrum of this system strongly depends on an external pump. For small and moderate pumps we reveal the presence of a doublet in the emission with the corresponding Rabi splitting scaling as a square root of the number of the excitations in the system. Further increase of the pump leads to the reshaping of the spectrum, which demonstrates the pattern typical for a Mollow triplet. An intermediate pumping regime shows a broad irregular spectrum reminiscent of a chaotic dynamics of the system.

Correlation between upstreamness and downstreamness in random global value chains
Silvia Bartolucci, Fabio Caccioli, Francesco Caravelli, Pierpaolo Vivo
arXiv:2303.06603v2 Announce Type: replace-cross Abstract: This paper is concerned with upstreamness and downstreamness of industries and countries in global value chains. Upstreamness and downstreamness measure respectively the average distance of an industrial sector from final consumption and from primary inputs, and they are computed from based on the most used global Input-Output tables databases, e.g., the World Input-Output Database (WIOD). Recently, Antr\`as and Chor reported a puzzling and counter-intuitive finding in data from the period 1995-2011, namely that (at country level) upstreamness appears to be positively correlated with downstreamness, with a correlation slope close to $+1$. This effect is stable over time and across countries, and it has been confirmed and validated by later analyses. We first analyze a simple model of random Input/Output tables, and we show that, under minimal and realistic structural assumptions, there is a natural positive correlation emerging between upstreamness and downstreamness of the same industrial sector/country, with correlation slope equal to $+1$. This effect is robust against changes in the randomness of the entries of the I/O table and different aggregation protocols. Secondly, we perform experiments by randomly reshuffling the entries of the empirical I/O table where these puzzling correlations are detected, in such a way that the global structural constraints are preserved. Again, we find that the upstreamness and downstreamness of the same industrial sector/country are positively correlated with slope close to $+1$, even though the random reshuffling has destroyed any underlying economic information about inter-sectorial connections and trends. Our results strongly suggest that the empirically observed puzzling correlation may rather be a necessary consequence of the few structural constraints that Input/Output tables must meet.

Semiclassical dynamics of a superconducting circuit: chaotic dynamics and fractal attractors
Davide Stirpe, Juuso Manninen, Francesco Massel
arXiv:2303.17492v2 Announce Type: replace-cross Abstract: We study here the semiclassical dynamics of a superconducting circuit constituted by two Josephson junctions in series, in the presence of a voltage bias. We derive the equations of motion for the circuit through a Hamiltonian description of the problem, considering the voltage sources as semi-holonomic constraints. We find that the dynamics of the system corresponds to that of a planar rotor with an oscillating pivot. We show that the system exhibits a rich dynamical behaviour with chaotic properties and we present a topological classification of the cyclic solutions, providing insight into the fractal nature of the dynamical attractors.

Effects of topological structure and destination selection strategies on agent dynamics in complex networks
Satori Tsuzuki, Daichi Yanagisawa, Eri Itoh, Katsuhiro Nishinari
arXiv:2305.06454v3 Announce Type: replace-cross Abstract: We analyzed agent behavior in complex networks: Barab\'asi-Albert (BA), Erdos-R\'enyi (ER), and Watts-Strogatz (WS) models under the following rules: agents (a) randomly select a destination among adjacent nodes; (b) exclude the most congested adjacent node as a potential destination and randomly select a destination among the remaining nodes; or (c) select the sparsest adjacent node as a destination. We focused on small complex networks with node degrees ranging from zero to a maximum of approximately 20 to study agent behavior in traffic and transportation networks. We measured the hunting rate, that is, the rate of change of agent amounts in each node per unit of time, and the imbalance of agent distribution among nodes. Our simulation study reveals that the topological structure of a network precisely determines agent distribution when agents perform full random walks; however, their destination selections alter the agent distribution. Notably, rule (c) makes hunting and imbalance rates significantly high compared with random walk cases (a) and (b), irrespective of network types, when the network has a high degree and high activity rate. Compared with the full random walk in (a), (b) increases the hunting rate while decreasing the imbalance rate when activity is low; however, both increase when activity is high. These characteristics exhibit slight periodic undulations over time. Furthermore, our analysis shows that in the BA, ER, and WS network models, the hunting rate decreases and the imbalance rate increases when the system disconnects randomly selected nodes in simulations where agents follow rules (a)-(c) and the network has the ability to disconnect nodes within a certain time of all time steps. Our findings can be applied to various applications related to agent dynamics in complex networks.

Current-induced near-field radiative energy, linear-momentum, and angular-momentum transfer
Huimin Zhu, Gaomin Tang, Lei Zhang, Jun Chen
arXiv:2312.07954v3 Announce Type: replace-cross Abstract: In this paper, we study the near-field radiative energy, linear-momentum, and angular-momentum transfer from a current-biased graphene to nanoparticles. The electric current through the graphene sheet induces nonequilibrium fluctuations, causing energy and momentum transfer even in the absence of a temperature difference. The inherent spin-momentum locking of graphene surface plasmons leads to an in-plane torque perpendicular to the direction of the electric current. In the presence of a temperature difference, the energy transfer is greatly enhanced while the lateral force and torque remain within the same order. Our work explores the potential of utilizing current-biased graphene to manipulate nanoparticles.

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In‐Plane Topological‐Defect‐Enriched Graphene as an Efficient Metal‐Free Catalyst for pH‐Universal H2O2 Electrosynthesis
Zhixing Mou, Yuewen Mu, Lijia Liu, Daili Cao, Shuai Chen, Wenjun Yan, Haiqing Zhou, Ting‐Shan Chan, Lo‐Yueh Chang, Xiujun Fan
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