In solids, electronic Bloch states are formed by atomic orbitals. While it is natural to expect that orbital composition and information about Bloch states can be manipulated and transported, in analogy to the spin degree of freedom extensively studied in past decades, it has been assumed that orbital quenching by the crystal field prevents significant dynamics of orbital degrees of freedom. However, recent studies reveal that an orbital current, given by the flow of electrons with a finite orbital angular momentum, can be electrically generated and transported in wide classes of materials despite the effect of orbital quenching in the ground state. Orbital currents also play a fundamental role in the mechanisms of other transport phenomena such as spin Hall effect and valley Hall effect. Most importantly, it has been proposed that orbital currents can be used to induce magnetization dynamics, which is one of the most pivotal and explored aspects of magnetism. Here, we give an overview of recent progress and the current status of research on orbital currents. We review proposed physical mechanisms for generating orbital currents and discuss candidate materials where orbital currents are manifest. We review recent experiments on orbital current generation and transport and discuss various experimental methods to quantify this elusive object at the heart of orbitronics —an area which exploits the orbital degree of freedom as an information carrier in solid-state devices.
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ISSN: 1286-4854
A Letters journal serving all areas of physics and its related fields, EPL publishes the highest quality research from around the world, and provides authors with fast, fair and constructive peer review thanks to an Editorial Board of active scientists, who are experts in their respective fields.
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Sauro Succi et al 2023 EPL 144 10001
We present a pedagogical introduction to the current state of quantum computing algorithms for the simulation of classical fluids. Different strategies, along with their potential merits and liabilities, are discussed and commented on.
Colin Benjamin and Ritesh Das 2024 EPL 146 16006
We propose a set of thermoelectric experiments based on Aharonov-Bohm interferometry to probe Majorana bound states (MBS), which are generated in 2D topological insulators (TI) in the presence of superconducting and ferromagnetic correlations via the proximity effect. The existence and nature (coupled or uncoupled) of these MBS can be determined by studying the charge and heat transport, specifically, the behavior of various thermoelectric coefficients like the Seebeck coefficient, Peltier coefficient, thermal conductance, and violations of Wiedemann-Franz law as a function of the Fermi energy and Aharonov-Bohm flux piercing the TI ring with the embedded MBS.
Francisco A. Rodrigues 2023 EPL 144 22001
Machine learning is a rapidly growing field with the potential to revolutionize many areas of science, including physics. This review provides a brief overview of machine learning in physics, covering the main concepts of supervised, unsupervised, and reinforcement learning, as well as more specialized topics such as causal inference, symbolic regression, and deep learning. We present some of the principal applications of machine learning in physics and discuss the associated challenges and perspectives.
Mahdi Nasiri et al 2023 EPL 142 17001
The question of how "smart" active agents, like insects, microorganisms, or future colloidal robots need to steer to optimally reach or discover a target, such as an odor source, food, or a cancer cell in a complex environment has recently attracted great interest. Here, we provide an overview of recent developments, regarding such optimal navigation problems, from the micro- to the macroscale, and give a perspective by discussing some of the challenges which are ahead of us. Besides exemplifying an elementary approach to optimal navigation problems, the article focuses on works utilizing machine learning-based methods. Such learning-based approaches can uncover highly efficient navigation strategies even for problems that involve, e.g., chaotic, high-dimensional, or unknown environments and are hardly solvable based on conventional analytical or simulation methods.
Charles Andrew Downing and Muhammad Shoufie Ukhtary 2024 EPL 146 10001
The challenge of storing energy efficiently and sustainably is highly prominent within modern scientific investigations. Due to the ongoing trend of miniaturization, the design of expressly quantum storage devices is itself a crucial task within current quantum technological research. Here we provide a transparent analytic model of a two-component quantum battery, composed of a charger and an energy holder, which is driven by a short laser pulse. We provide simple expressions for the energy stored in the battery, the maximum amount of work which can be extracted, both the instantaneous and the average powers, and the relevant charging times. This allows us to discuss explicitly the optimal design of the battery in terms of the driving strength of the pulse, the coupling between the charger and the holder, and the inevitable energy loss into the environment. We anticipate that our theory can act as a helpful guide for the nascent experimental work building and characterizing the first generation of truly quantum batteries.
Zeynep Çoker et al 2023 EPL 143 59001
Based on the fractional black-hole entropy (Jalalzadeh S. et al., Eur. Phys. J. C, 81 (2021) 632), we derive the modified Friedmann equations from two different frameworks. First, we consider the modifications of Friedmann equations from the first law of thermodynamics at the apparent horizon. We show that the generalized second law (GSL) of thermodynamics always holds in a region bounded by the apparent horizon. Then, we obtain Friedmann equations from Verlinde's entropic gravity framework. We also compute the fractional corrections to the deceleration parameter q in the flat case k = 0 for both frameworks. Furthermore, we consider the time to reach the initial singularity for the two frameworks. The results indicate that the initial singularity is accessible for both frameworks. However, fractional effects may provide a constraint on the equation-of-state parameter in the entropic gravity scenario since the time is imaginary for .
Vaibhav Raj Singh Parmar and Ranjini Bandyopadhyay 2024 EPL 145 47001
The growth of interfacial instabilities during fluid displacements can be driven by gradients in pressure, viscosity and surface tension, and by applying external fields. Since displacements of non-Newtonian fluids such as polymer solutions, colloidal and granular slurries are ubiquitous in natural and industrial processes, understanding the growth mechanisms and fully developed morphologies of interfacial patterns involving non-Newtonian fluids is extremely important. In this perspective, we focus on displacement experiments, wherein competitions between capillary, viscous, elastic and frictional forces drive the onset and growth of primarily viscous fingering instabilities in confined geometries. We conclude by highlighting several exciting open problems in this research area.
Min Liu et al 2024 EPL 146 21001
Network resilience measures complex systems' ability to adjust its activity to retain the basic functionality for systematic errors or failures, which has attracted increasingly attention from various fields. Resilience analyses play an important role for early warning, prediction, and proposing potential strategies or designing optimal resilience systems. This letter reviews the advanced progress of network resilience from three aspects: Resilience measurement, resilience analysis, as well as resilience recovery strategies. We outline the challenges of network resilience which should be investigated in the future.
Haoran Liu et al 2024 EPL 145 61001
Network science has already been fruitful and confirmed effective on the description of real-world or abstract systems. An increasing number of researches and instances have successfully verified, however, that interactions in systems may occur among three, four, or even more components. The introduction of higher-order perspective brings a revolution on network science, and refreshes researchers' understanding of synchronization. Hence, an overview is presented here in regard of synchronization on higher-order networks. We start from an introduction of how the higher-order networks are represented using algebraic tools. Then a series of landmark researches on synchronization is reviewed under circumstances of whether or not the dynamics contains control. Finally, we summarize our conclusions and propose our outlooks on expectations of future works.
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Davide Venturelli et al 2024 EPL 146 27001
We develop a framework for the stochastic thermodynamics of a probe coupled to a fluctuating medium with spatio-temporal correlations, described by a scalar field. For a Brownian particle dragged by a harmonic trap through a fluctuating Gaussian field, we show that near criticality (where the field displays long-range spatial correlations) the spatially-resolved average heat flux develops a dipolar structure, where heat is absorbed in front and dissipated behind the dragged particle. Moreover, a perturbative calculation reveals that the dissipated power displays three distinct dynamical regimes depending on the drag velocity.
Chaitra Chooda Chalavadi and V. Venkatesha 2024 EPL 146 39001
The aim of this manuscript is to study traversable wormhole geometries in the non-metricity and matter coupling gravity. We investigate the Morris-Thorne wormhole metric within the framework of extended symmetric teleparallel gravity. With an anisotropic matter distribution, we explore two distinct wormhole models under two different scenarios. First, we consider the equations of state, and then we assume specific shape functions for each scenario. In both cases, the shape function satisfies all fundamental criteria for a traversable wormhole. We present our results through graphical representations and analyze the energy conditions. Furthermore, we examine the behavior of the wormhole through the anisotropic parameter. Finally, we present our conclusions based on the obtained results.
P. A. Varotsos et al 2024 EPL 146 22001
Upon employing the new concept of time, termed natural time, the analysis of seismicity reveals that, before major earthquakes, the variations of the Earth's electric and/or magnetic field are accompanied by increase of the fluctuations of the entropy change of seismicity under time reversal as well as by decrease of the fluctuations of the seismicity order parameter. Hence, natural time analysis reveals that before major earthquakes independent datasets of different geophysical observables (seismicity, Earth's magnetic and/or electric field) exhibit changes, which are observed simultaneously.
To the memory of the Academician Seiya Uyeda.
Hongying Yang et al 2024 EPL 146 38002
In the field of quantum thermometry, usually temperature is estimated by the framework of quantum metrology. In this work, an alternative approach to quantum thermometry is suggested, based on interferometric power (IP). IP is defined as the worst-case quantum Fisher information in a double-channel interferometer. Specifically, the time evolution of the IP for a two-qubit state as a probe contacting with a finite-temperature bath is considered. The IP dynamics of the probe with three kinds of initial states (i.e., entangled, separable, and mixed) strongly depend on the bath temperature. The dynamical evolution of IP would be measured experimentally, considering that the IP is a measurable quantity in the experiment. Thus, the IP dynamics can be adopted to extract the value of the bath temperature directly. In this sense, the IP could be exploited as a quantum thermometer.
Arunoday Sarkar and Buddhadeb Ghosh 2024 EPL 146 29002
We derive an potential of slow-roll inflation in the warped D brane set-up featuring three intersecting D7 branes under type of CY3-compactification within type-IIB/F theory with some near-conifold regions. The underlying quadratic structure of the kinetic poles is found to arise from a correction in the Kähler potential when an extra contribution of open string moduli is turned on. While the closed string sector of the moduli spectrum is completely stabilized via quantum corrections of perturbative and non-perturbative origin, the open string sector plays the lead role in driving the inflationary expansion in the radial direction. A generic asymptotic behaviour of the inflaton field near the pole boundaries manifests itself as the slow-roll plateau in canonical field space, which becomes responsible for giving universal predictions of the cosmological parameters. We find that the presence of the open strings near conifold regions brings the realization of pole inflation in the present set-up. Finally we compare our results with similar models and discuss the importance of exploring precise values of α in the light of ongoing and forthcoming cosmological surveys.
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Mondal et al
In this work, we investigate the interplay between correlated disorder and hopping dimerization on bias driven circular
current in a loop conductor that is clamped between two electrodes. The correlated disorder is introduced in site energies of the
ring in the form of Aubry-Andr\'e-Harper (AAH) model. Simulating the quantum system within a tight-binding framework all the results
are worked out based on the wave-guide theory. Unlike transport current, circular current in the loop conductor can get
enhanced with increasing disorder strength. This enhancement becomes much effective when hopping dimerization is included which is
taken following the Su-Schrieffer-Heeger (SSH) model. The characteristic features of bias driven circular current are studied under
different input conditions and we find the results are robust for wide range of physical parameters. For the sake
of completeness, uncorrelated disorder is also considered. Our analysis may provide a new insight in analyzing transport behavior
in different disordered lattices in presence of additional restrictions in hopping integrals.
Watson
Identifying possible microscopic mechanisms underlying superfluidity has been the goal of various studies since the introduction of the original BCS theory. Recently a series of papers have proposed microscopic dynamics based on normal modes to describe superfluidity without the use of real-space Cooper pairs. Multiple properties were determined with excellent agreement with experimental data. The group theoretic basis of this general N-body approach has allowed the microscopic behavior underlying these results to be analyzed in detail. This reimagination is now used to reinterpret several interrelated phenomena including Cooper pairs, the Fermi sea, and Pauli blocking. This approach adheres closely to the early tenets of superconductivity/superfluidity which assumed pairing only in momentum space, not in real space. The Pauli principle is used, in its recently revealed role in collective motion, to select the allowed normal modes. The expected properties of superfluidity including the rigidity of the wave function, interactions between the fermions in different pairs, convergence of the momentum and the gap in the excitation spectrum are discussed.
Xin et al
We examined the effect of the lattice compression on the crystal structure of the Bi2Sr2CaCu2O8+δsuperconductor with nearly optimally doped and overdoped composition using x-ray diffraction technique. Our studies show that at high pressures (up to 30 GPa) the doping level does not affect the crystal structure of this superconductor. Along with this, structural anomalies in c/a ratio appear at a pressure that corresponds to that at which Tc begins to decrease. This fact indicates a close connection between the observed anomalies and superconductivity. We also studied the effect of doping and pressure on the Tc(P) and on the Raman active lattice modes of the Bi2Sr2CaCu2O8+δ superconductors. We find universal suppression of the Tc by the pressure starting from the critical pressure Pc in the range from 9 to 16 GPa, depending on the doping level of the Bi2Sr2CaCu2O8+δsamples. Concomitantly, we observe phonon anomalies around 10 to 20 GPa, which indicate possible pressure-induced charge redistribution in BiO layers. These newly detected anomalies may be related to the changes in the electronic structure which compete with the superconductivity.
Skeivalas et al
An ability to construct predictive models for identifying seismic oscillation parameters by using the mathematics of covariance functions and Doppler effect phenomena is examined in this work. In the calculations, the Mars seismic oscillations measurement data from InSight Mission V2, observed in the months 05, 06 and 07 of 2019, was used. To analyze the observation data arrays the Doppler phenomena and the expressions of covariance functions were employed. The seismic oscillations trend's intensity vectors were assessed by least squares method, and the random errors of measurements at the stations were eliminated partially as well. The estimates of the vector's auto-covariance and cross-covariance functions were derived by altering the quantization interval on the general time scale while varying the magnitude of the seismic oscillation vector on the same time scale. To detect the mean values of z – the main parameter of Doppler expression - we developed formula by involving the derivatives of cross-covariance functions of a single vector and algebraic sum of the relevant vectors.
Touil et al
Recent advances in quantum information science have shed light on the intricate dynamics of quantum many-body systems, for which quantum information scrambling is a perfect example. Motivated by considerations of the thermodynamics of quantum information, this perspective aims at synthesizing key findings from several pivotal studies, exploring various aspects of quantum scrambling. We consider quantifiers such as the Out-of-Time-Ordered Correlator (OTOC), the quantum Mutual Information, and the Tripartite Mutual Information (TMI), their connections to thermodynamics, and their role in understanding chaotic versus integrable quantum systems. Focusing on representative examples, we cover a range of topics, including the thermodynamics of quantum information scrambling, and the scrambling dynamics in quantum gravity models such as the Sachdev-Ye-Kitaev (SYK) model. By examining these diverse approaches, we highlight the multifaceted nature of quantum information scrambling and its significance in understanding the fundamental aspects of quantum many-body dynamics at the intersection of quantum mechanics and thermodynamics.
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Open all abstracts, in this tab
Davide Venturelli et al 2024 EPL 146 27001
We develop a framework for the stochastic thermodynamics of a probe coupled to a fluctuating medium with spatio-temporal correlations, described by a scalar field. For a Brownian particle dragged by a harmonic trap through a fluctuating Gaussian field, we show that near criticality (where the field displays long-range spatial correlations) the spatially-resolved average heat flux develops a dipolar structure, where heat is absorbed in front and dissipated behind the dragged particle. Moreover, a perturbative calculation reveals that the dissipated power displays three distinct dynamical regimes depending on the drag velocity.
P. A. Varotsos et al 2024 EPL 146 22001
Upon employing the new concept of time, termed natural time, the analysis of seismicity reveals that, before major earthquakes, the variations of the Earth's electric and/or magnetic field are accompanied by increase of the fluctuations of the entropy change of seismicity under time reversal as well as by decrease of the fluctuations of the seismicity order parameter. Hence, natural time analysis reveals that before major earthquakes independent datasets of different geophysical observables (seismicity, Earth's magnetic and/or electric field) exhibit changes, which are observed simultaneously.
To the memory of the Academician Seiya Uyeda.
Jonas Skeivalas et al 2024 EPL
An ability to construct predictive models for identifying seismic oscillation parameters by using the mathematics of covariance functions and Doppler effect phenomena is examined in this work. In the calculations, the Mars seismic oscillations measurement data from InSight Mission V2, observed in the months 05, 06 and 07 of 2019, was used. To analyze the observation data arrays the Doppler phenomena and the expressions of covariance functions were employed. The seismic oscillations trend's intensity vectors were assessed by least squares method, and the random errors of measurements at the stations were eliminated partially as well. The estimates of the vector's auto-covariance and cross-covariance functions were derived by altering the quantization interval on the general time scale while varying the magnitude of the seismic oscillation vector on the same time scale. To detect the mean values of z – the main parameter of Doppler expression - we developed formula by involving the derivatives of cross-covariance functions of a single vector and algebraic sum of the relevant vectors.
Hisa-Aki Tanaka et al 2024 EPL
Synchronisability of limit cycle oscillators has been measured by the width of the synchronous frequency band, known as the Arnold tongue, concerning external forcing.
We clarify a fundamental limit on maximizing this synchronisability within a specified extra low power budget, which underlies an important and ubiquitous problem in nonlinear science related to an efficient synchronisation of weakly forced nonlinear oscillators.
In this letter, injection-locked Class-E oscillators are considered as a practical case study, and we systematically analyse their power consumption;
our observations demonstrate the independence of power consumption in the oscillator from power consumption in the injection circuit and verify the dependency of power consumption in the oscillator solely on its oscillation frequency.
These systematic observations, followed by the mathematical optimisation establish the existence of a fundamental limit on synchronisability, validated through systematic circuit simulations.
The results offer insights into the energetics of synchronisation for a specific class of injection-locked oscillators.
George Livadiotis and David McComas 2024 EPL
This paper reveals the universality of the particle energy distribution function, despite the arbitrariness that characterizes the generalized thermodynamic entropic function. We show that the canonical distribution, that is, the distribution function that maximizes this entropy under the constraints of canonical ensemble, is always the same and given by the kappa distribution function. We use the recently developed entropy defect to express the generalized entropic formulation. The entropy defect is a thermodynamic concept that describes the loss of entropy due to the order induced by the presence of correlations. Then we carry out functional analysis to maximize the implicit expression of the generalized entropy. Critically, we show that the Lagrange multipliers have the same exact arbitrariness as the generalized entropic function, allowing us to cancel it out and proving the universality of canonical distribution as the kappa distribution function.
Jeremiah Lübke et al 2024 EPL
Synthetic turbulence is a relevant tool to study complex astrophysical and space plasma environments inaccessible by direct simulation. However, conventional models lack intermittent coherent structures, which are essential in realistic turbulence. We present a novel method featuring coherent structures, conditional structure function scaling and fieldline curvature statistics comparable to magnetohydrodynamic turbulence. Enhanced transport of charged particles is investigated as well. This method presents significant progress towards physically faithful synthetic turbulence.
Arkady P. Zhukov et al 2024 EPL
A unique combination of unusual magnetic properties, such as magnetic bistability associated with ultrafast domain wall propagation or ultrasoft magnetic properties, together with excellent mechanical and corrosion properties can be obtained in amorphous microwires. Such ferromagnetic microwires coated with insulating and flexible glass-coating with diameters ranging from 0.1 to 100 µm can be prepared using the Taylor-Ulitovsky method. Magnetic properties of glass-coated microwires are affected by chemical compositions of the metallic nucleus and can be substantially modified by post-processing. We provide an overview of the routes allowing tuning of hysteresis loops and domain wall dynamics in amorphous microwires and new experimental results on the dependence of hysteresis loops on exter-nal stimuli, such as applied stress and temperature.
Qi Gao et al 2024 EPL
We analyze the static response to kinetic perturbations of nonequilibrium steady states that can be modeled as diffusions. We demonstrate that kinetic response is purely a nonequilibirum effect, measuring the degree to which the Fluctuation-Dissipation Theorem is violated out of equilibrium. For driven diffusions in a flat landscape, we further demonstrate that such response is constrained by the strength of the nonequilibrium driving via quantitative inequalities.
Ellen Luckins et al 2024 EPL
We consider a liquid containing impurities saturating a porous material; when the liquid evaporates, the impurities are deposited within the material. Applications include filtration and waterproof textiles. We present a mathematical model incorporating coupling between evaporation, accumulation and transport of the impurities, and the impact of the deposited impurities on the transport of both the suspended impurities and the liquid vapour. By simulating our model numerically, we investigate the role of temperature and repeated drying cycles on the location of the deposited impurities. Higher temperatures increase the evaporation rate so that impurities are transported further into porous material before depositing than for lower temperatures. We quantify two distinct parameter regimes in which the material clogs: (i) the dry-clogging (high-temperature) regime, in which impurities are pushed far into the material before clogging, and (ii) the wet-clogging (high-impurity) regime, in which liquid becomes trapped by the clogging. Clogging restricts the extent to which drying time can be reduced by increasing the temperature.
Charles Andrew Downing and Muhammad Shoufie Ukhtary 2024 EPL 146 10001
The challenge of storing energy efficiently and sustainably is highly prominent within modern scientific investigations. Due to the ongoing trend of miniaturization, the design of expressly quantum storage devices is itself a crucial task within current quantum technological research. Here we provide a transparent analytic model of a two-component quantum battery, composed of a charger and an energy holder, which is driven by a short laser pulse. We provide simple expressions for the energy stored in the battery, the maximum amount of work which can be extracted, both the instantaneous and the average powers, and the relevant charging times. This allows us to discuss explicitly the optimal design of the battery in terms of the driving strength of the pulse, the coupling between the charger and the holder, and the inevitable energy loss into the environment. We anticipate that our theory can act as a helpful guide for the nascent experimental work building and characterizing the first generation of truly quantum batteries.