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Entropy 2017, 19(1), 20; doi:10.3390/e19010020

Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems

1
Dipartimento di Fisica e Chimica, Interdisciplinary Theoretical Physics Group, Università di Palermo and CNISM, Unità di Palermo, Viale delle Scienze, Edificio 18, I-90128 Palermo, Italy
2
Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Catania, Italy
3
Radiophysics Department, Lobachevsky State University of Nizhni Novgorod, Nizhni Novgorod, Russia
4
SPIN-CNR, Via Dodecaneso 33, I-16146 Genova, Italy
5
NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, I-56127 Pisa, Italy
6
Institute of Physics, University of Augsburg, Universitätsstrasse 1, D-86135 Augsburg, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Kevin H. Knuth
Received: 12 November 2016 / Revised: 22 December 2016 / Accepted: 25 December 2016 / Published: 31 December 2016
(This article belongs to the Special Issue Nonequilibrium Phenomena in Confined Systems)
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Abstract

Nonlinear relaxation phenomena in three different systems of condensed matter are investigated. (i) First, the phase dynamics in Josephson junctions is analyzed. Specifically, a superconductor-graphene-superconductor (SGS) system exhibits quantum metastable states, and the average escape time from these metastable states in the presence of Gaussian and correlated fluctuations is calculated, accounting for variations in the the noise source intensity and the bias frequency. Moreover, the transient dynamics of a long-overlap Josephson junction (JJ) subject to thermal fluctuations and non-Gaussian noise sources is investigated. Noise induced phenomena are observed, such as the noise enhanced stability and the stochastic resonant activation. (ii) Second, the electron spin relaxation process in a n-type GaAs bulk driven by a fluctuating electric field is investigated. In particular, by using a Monte Carlo approach, we study the influence of a random telegraph noise on the spin polarized transport. Our findings show the possibility to raise the spin relaxation length by increasing the amplitude of the external fluctuations. Moreover, we find that, crucially, depending on the value of the external field strength, the electron spin depolarization length versus the noise correlation time increases up to a plateau. (iii) Finally, the stabilization of quantum metastable states by dissipation is presented. Normally, quantum fluctuations enhance the escape from metastable states in the presence of dissipation. We show that dissipation can enhance the stability of a quantum metastable system, consisting of a particle moving in a strongly asymmetric double well potential, interacting with a thermal bath. We find that the escape time from the metastable region has a nonmonotonic behavior versus the system- bath coupling and the temperature, producing a stabilizing effect. View Full-Text
Keywords: metastability; nonequilibrium statistical mechanics and nonlinear relaxation time; noise enhanced stability; Josephson junction; spin polarized transport in semiconductors; open quantum systems; quantum noise enhanced stability metastability; nonequilibrium statistical mechanics and nonlinear relaxation time; noise enhanced stability; Josephson junction; spin polarized transport in semiconductors; open quantum systems; quantum noise enhanced stability
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Spagnolo, B.; Guarcello, C.; Magazzù, L.; Carollo, A.; Persano Adorno, D.; Valenti, D. Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems. Entropy 2017, 19, 20.

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