Condensed-Matter Physics & Materials Science Seminar

The existence of an equilibrium persistent current (PC) in a non-superconducting mesoscopic system having a finite resistance [1,2] is one of the surprising fundamental results that characterize the Physics on these scales. We consider the magnitude of these currents in a very low-temperature superconductor with a bare transition temperature much smaller than the Thouless [3] energy. To resolve the long-standing discrepancy between the theoretical [4,5] and experimental [2] values (especially for Copper) for the magnitude of the average currents for the noble metals, we capitalize on the recent finding [6] that these metals almost always have some magnetic impurities which dominate their dephasing rates at low T. We show that in a rather broad range of pair-breaking rates, much larger than the bare transition temperature, but much smaller than the Thouless scale, the transition temperature is renormalized to zero, but the PC is hardly affected. This increases the predicted magnitudes of the PC and may provide an explanation for the values (and signs) of the average PC's in Copper2, as well as a way to determine their "bare" transition tempertures (those that would exist without the pair-breaking magnetic impurities). This work can be found in Cond-Mat 0804.0702 and Phys. Rev. Lett., 101, 057001 (2008). It is reviewed by H. Bouchiat in http://physics.aps.org/articles/v1/7.
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