Persistent current in normal metals

Abstract

We discuss the recent experiments on persistent current in metallic rings in the backdrop of low temperature decoherence. The observed size of the persistent current, typically on the order of the Thouless energy, e/τD, is much larger than the theoretical results, obtained with or without electron interaction. In considering the phenomenology of both decoherence and persistent current, usually observed in similar systems, we argue towards a dynamic role played by decoherence in the generation of a persistent current. A field-induced phase shift from near-equilibrium high-frequency fluctuations-which otherwise gives rise to decoherence-under certain conditions of periodicity and asymmetry due to disorder, is argued to induce a steady state diffusion current on the order of e/τD, comparable to the observed persistent current.

Many-body physics and quantum chaos

“…However the magnitude of the average persistent current appears to be quite a bit larger (a factor three to five) than what is expected theoretically (Ambegaokar & Eckern 1990a). It has been suggested that this large magnetic response might be related to non-equilibrium effects, such as the coupling to a phonon or photon bath (Mohanty 1999, Kravtsov & Altshuler 2000, Entin-Wohlman et al 2003. In later experiments (Jariwala et al 2001) (see also Reulet et al (1995) and Deblock et al (2002) in this context), a further, and presumably more dramatic, discrepancy is that the sign of the magnetic response -which has not been determined in Lévy et al (1990) -was furthermore not the one expected for a repulsive interaction.…”

Of Decoherent Electrons and Disordered Conductors

“…Recent experiments, however, have challenged this traditional picture. These include the topics of the current paper, saturation of decoherence time at low temperature [10], large persistent current in normal metals [11] and metallic states in two dimensions [12]; it appears that the single-particle picture may be inadequate in explaining these phenomena.…”

“…Normal-metal phase-coherent rings exhibit persistent currents because of electron interference [5,6,11]. The presence of an Aharonov-Bohm flux Φ introduces a phase factor into the boundary condition for the electron wave function,…”

“…; decoherence time extracted from persistent current at low temperatures shows the saturation [11], consistent with the weak localization measurements on similar control samples [10].…”

“…In particular, an environment producing temperature-independent electric field fluctuations (in time) can result in a temperature-independent decoherence time τ 0 and a large persistent current I PC . These two quantities are related to each other with a form specific to the environment [11,26]. For example, the current arising from a high-frequency noise source is given by n denotes the flux harmonic of the current, and C β is a constant of the order one.…”