Paramagnetic Meissner effect in voltage-biased proximity systems

Abstract

Conventional superconductors respond to external magnetic fields by generating diamagnetic screening currents. However, theoretical work has shown that one can engineer systems where the screening current is paramagnetic, causing them to attract magnetic flux-a prediction that has recently been experimentally verified. In contrast to previous studies, we show that this effect can be realized in simple superconductor/normal-metal structures with no special properties, using only a simple voltage bias to drive the system out of equilibrium. This is of fundamental interest, since it opens up a new avenue of research, and at the same time highlights how one can realize paramagnetic Meissner effects without having odd-frequency states at the Fermi level. Moreover, a voltage-tunable electromagnetic response in such a simple system may be interesting for future device design.Introduction.-Conventional superconductors have two defining properties [1, 2]. The first is their perfect conductance of electric currents, from which they derive their name. The second is the so-called Meissner effect, whereby dissipationless electric currents screen magnetic fields. Both properties arise due to a coherent condensate of electron pairs (Cooper pairs) which exhibits spontaneous symmetry breaking, and it is of fundamental interest to understand both in depth.