Anomalous transport due to retroreflection
| Autor: | Klaus Pierz, René Lohmann, Hans Werner Schumacher, J. Schluck, Beate Horn-Cosfeld, Thomas Heinzel, Dominique Mailly, Nima H. Siboni, Jürgen Horbach |
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| Přispěvatelé: | Centre de Nanosciences et de Nanotechnologies (C2N), Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS) |
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Physics
Condensed matter physics Field (physics) Anomalous diffusion Order (ring theory) 01 natural sciences Power law 010305 fluids & plasmas Magnetic field Molecular dynamics 0103 physical sciences Diffusion (business) 010306 general physics Fermi gas [PHYS.COND.CM-MSQHE]Physics [physics]/Condensed Matter [cond-mat]/Mesoscopic Systems and Quantum Hall Effect [cond-mat.mes-hall] |
| Zdroj: | Physical Review B Physical Review B, American Physical Society, 2020, 102, ⟨10.1103/physrevb.102.081302⟩ |
| ISSN: | 2469-9950 2469-9969 |
| DOI: | 10.1103/physrevb.102.081302⟩ |
| Popis: | International audience; The magnetotransport of an electron gas in a two-dimensional, random arrangement of overlapping retrore-flective crosses is studied using a combination of experiment and classical event-driven molecular dynamics simulation. The experimentally measured magnetoconductivity σ xx as a function of the magnetic field B displays an anomalous behavior at low B fields, accompanied with an increase of σ xx with increasing temperature at B = 0. The simulations show that at B = 0 the magnetoconductivity does not exist and is associated with anomalous diffusion in the asymptotic long-time limit that depends on the orientational order of the obstacles. At any finite B field, the motion of the tracer particle is asymptotically diffusive but the diffusion coefficient vanishes with a power law in the limit B → 0. Introduction. Anomalous diffusion processes such as sub-and superdiffusion are ubiquitous in heterogeneous media [1-3]. However, there are only a few particle-based model systems that exhibit anomalous diffusion as an asymptotic process in the long-time limit. A celebrated example in this context is the disordered Lorentz gas (LG) [4] where, in its simplest version, a tracer particle probes the void space of a random arrangement of overlapping spherical objects. In this model, a conductor-insulator transition at a critical obstacle density n c coincides with the percolation transition of the obstacles, implying subdiffusion due to the fractal structure of the free space at n c [3,5-16]. Evidence for a completely different type of asymptotic subdiffusion has been found for Ehrenfest's wind-tree (EWT) model [17]. Here, a point tracer particle moves through the void space of a two-dimensional (2D) random arrangement of overlapping or nonoverlapping squares. The flat boundaries of the squares induce retracing events (or retroreflections) where the tracer particle is reflected back such that even in short-time windows it returns several times to a region where it has been earlier. For overlapping squares, kinetic theory for low densities [18-20] predicts that the multiple backscattering events of the tracer particle result in a mean-squared displacement (MSD) with an asymptotic sublinear growth in the long-time limit δr 2 (t) ∝ t 1−4n /3 (with n = na 2 a dimensionless obstacle density, where n is the number density of the squares and 2a the length of their diagonals). An early simulation study [21] has qualitatively confirmed the existence of anomalous diffusion in the EWT model with overlapping squares. These results for the EWT model raise many unsolved questions about anomalous transport in heterogeneous 2D |
| Databáze: | OpenAIRE |
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