EPL (Europhysics Letters)

Journal Information
ISSN / EISSN : 0295-5075 / 1286-4854
Published by: IOP Publishing (10.1209)
Total articles ≅ 20,672
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, DaeGeun Jo, Hyun-Woo Lee, Mathias Klaeui, Yuriy Mokrousov
Published: 13 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac2653

Abstract:
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.
Published: 13 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac2654

Abstract:
We relate the anomaly in the noise color of spin ice to the emergent nature of its magnetic monopoles and their random walk. Monopoles are quasi-particles, and the spin vacuum in which they wander is not structureless. Rather, the underlying spin ensemble filters the thermal white noise, leading to non-trivial coevolution. Thus, monopoles can be considered as "dressed" random walkers, activated by a non-trivial stochastic noise that subsumes mutual interactions and the coevolution of their spin vacuum. From this, we suggest that recent experimental results are interpretable in terms of monopole subdiffusion. We then conjecture relations between the color of the noise and other observables, such as relaxation time, monopole density, the dynamic exponent, and the order of the annihilation reaction, which suggests to us the introduction of spin-ice-specific critical exponents in a neighborhood of the ice manifold criticality.
Published: 13 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac2655

Abstract:
Dry sliding friction is a complex but ubiquitous phenomenon. Experimental studies of friction produce large amounts of data, while most models are phenomenological rather than deduced from fundamental principles. Proper identification of relevant degrees of freedom is crucial for the development of adequate frictional models, such as the state-and-rate models. Topological data analysis is a mathematical method for the dimensionality reduction for datasets characterizing surface roughness, contact of rough surfaces and frictional sliding. We study tribological systems including the surface roughness and multiasperity contacts using 3×3, 4×4, and 5×5 pixel patches. Depending on whether the surface is isotropic or anisotropic with particular lay directions, the data tends to concentrate at certain "primary" and "secondary" circles yielding different values of the Betti numbers. Scale dependency of corresponding structures is analyzed with persistence diagrams. Moreover, statistics of stick-slip zones can provide insights on relevant internal degrees of friction.
Liming Zhao, Yun-Song Zhou, Gong-Min Wei
Published: 13 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac2652

Abstract:
The finding of Photon Hall effect (PHE) on metal surface is an important progress in photonics, but it will be more practical if PHE can be realized in line-type waveguide. In this paper, we suggested a way to realize PHE in two-dimensional photonic crystal (PC) waveguide. Numerical simulation results show that the propagating direction and strength of light in the PC waveguide can be controlled by the polarization state of incident light. Different from the PHE on metal surface, the PHE in PC waveguide can be driven not only by circularly polarized light, but also by linearly polarized light. The PHE in PC waveguide can be attributed to the interference of the two component waves excited by the incident light.
Hongxia Huang, Xin Jin, Yue Tan, Jialun Ping
Published: 10 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac25aa

Abstract:
In recent two decades, a large number of exotic hadron states have been observed in experiments, which arouses great attentions in hadron physics community. In this short review, we briefly summarize progresses of our group on several exotic hadron states. Two approaches, quenched and unquenched quark models, are adopted in the calculation. The channel coupling effects, the multiquark states couple to open-channels and the quark-antiquark states couple to meson-meson states, are emphasized. X(3872) is showed to be a mixture state of ccbar and DDbar* in the unquenched quark model. X(2900) can be explained as a resonance state Dbar*K* with the quantum numbers IJP=00+ in both the quark delocalization color screening model and the chiral quark model. The reported state X(6900) can be explained as a compact resonance state with IJP=00+ in both two quark models, and several fully heavy tetraquark states are predicated. The possible hidden-charm pentaquarks are systematically investigated in QDCSM, and seven resonance states are obtained in the corresponding baryon-meson scattering process, among which the ΣcD with JP=1/2-, ΣcD* with JP=3/2- and JP=1/2- are consistent with the experimental report of Pc(4312), Pc(4440), and Pc(4457), respectively. Experimental search for more exotic hadron states will provide more information for understanding the exotic hadron states in quark models.
, Pierre Le Doussal
Published: 10 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac25a9

Abstract:
We obtain a simple formula for the stationary measure of the height field evolving according to the Kardar-Parisi-Zhang equation on the interval [0, L] with general Neumann type boundary conditions and any interval size. This is achieved using the recent results of Corwin and Knizel (arXiv:2103.12253) together with Liouville quantum mechanics. Our formula allows to easily determine the stationary measure in various limits: KPZ fixed point on an interval, half-line KPZ equation, KPZ fixed point on a half-line, as well as the Edwards-Wilkinson equation on an interval.
, A. K. Rao
Published: 10 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac25a8

Abstract:
We demonstrate that the standard St{$\ddot u$}ckelberg-modified Proca theory (i.e. a massive Abelian 1-form theory) respects the classical gauge and corresponding quantum (anti-)BRST symmetry transformations in any arbitrary dimension of spacetime within the framework of Becchi-Rouet-Stora-Tyutin (BRST) formalism. We further show that the St{$\ddot u$}ckelberg formalism gets modified in the two (1+1)-dimensions of spacetime due to a couple of discrete duality symmetry transformations in the theory which turn out to be responsible for the existence of the nilpotent (anti-)co-BRST symmetry transformations corresponding to the nilpotent (anti-)BRST symmetry transformations of our theory. These nilpotent symmetries exist together in the modified version of the two (1+1)-dimensional (2D) Proca theory. We provide the mathematical basis for the modification of the St{$\ddot u$}ckelberg-technique, the existence of the discrete duality as well as the continuous (anti-)co-BRST symmetry transformations in the 2D modified version of Proca theory.
João Paulo Morais Graça, , Henrique Boschi-Filho
Published: 8 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac24c1

Abstract:
In this work we study the Joule-Thomson expansion for uncharged black holes in a noncommutative scenario characterized by a parameter θ, which is present in the horizon function. We calculate the inversion temperature for some values of θ and the isenthalpics for fixed masses. We find that the uncharged noncommutative black hole behaves as a charged commutative one.
, Hugo Fort
Published: 7 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac2457

Abstract:
In evolutionary game theory, pair interactions are usually defined through so-called payoff matrices, which can be decomposed as linear combinations of basis matrices that represent just four different orthogonal interaction types. In this paper, we take the first steps in exploring the utility of this decomposition in ecology. We introduce the componental cosines of the irrelevant, external, coordination, and conflict components of matrices to measure the relative weight of the different interaction types, and use them to analyse the composition of 33 experimentally obtained interspecific interaction matrices compiled from the literature, which reveals statistically significant correlations both between different components and some components and community productivity and biodiversity.
Mohd Alam, Arkadeb Pal, Khyati Anand, Surajit Ghosh, Saurabh Tripathi, Ranjan Kumar Singh, Anup K. Ghosh, H. D. Yang, Sandip Chatterjee
Published: 7 September 2021
EPL (Europhysics Letters); https://doi.org/10.1209/0295-5075/ac2455

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