Wednesday, June 19, 2013

1306.4268 (Valentin Stanev et al.)

Complex state induced by impurities in multiband superconductors    [PDF]

Valentin Stanev, Alexei E. Koshelev
In this paper we study the role of impurities in a two-band superconductor. We elucidate the nature of the recently predicted transition from s_{+-} state to s_{++} state induced by interband impurity scattering. Using a Ginzburg-Landau theory, derived from microscopic equations, we demonstrate that close to T_c this transition is necessarily a direct one, but deeper in the superconducting state an intermediate complex state appears. This state has a distinct order parameter, which breaks the time-reversal symmetry, and is separated from the s_{+-} and s_{++} states by phase transitions. Based on our results, we suggest a phase diagram for systems with weak repulsive interband pairing, and discuss its relevance to iron-based superconductors.
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