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A.E. Koshelev - Materials Science Division, Argonne National Laboratory, USA

Anomalous proximity effects between s and s+- superconductors

The s+- state in which the order parameter has opposite signs in the electron and hole bands is the leading candidate for superconducting state in the ironbased superconductors. We study proximity effects between s and s+- superconductors. Frustration, caused by interaction of the s-wave gap parameter
with the opposite-sign gaps of s+- superconductor, leads to several anomalous features. In the case of strong frustration, a nontrivial time-reversal-symmetry breaking (TRSB) state, with nonzero phase angles between all gap parameters, is possible. In a more typical state, the s-wave order parameter is aligned with one of the s+- gaps. We study this system using a simple microscopic model assuming dirty limit in all bands. Using this microscopic theory in the regime of weak coupling between the superconductors, we established the range of parameters where the TRSB state is realized. In the aligned state the s+- gaps aligned with the s-wave order parameter induce positive features in the s-wave density of states while the anti-aligned gaps
induce negative features. These negative features may serve as fingerprints of s+- state. Another consequence of the frustration is an extended region in the parameter space in which s-wave superconductivity is suppressed despite being in contact with nominally stronger superconductor (negative proximity effect). This effect is always present for the TRSB state, but also considerably
extends into the aligned states. Observation of these anomalous features would provide a proof for the s+- state in the iron-based superconductors.



C.J. van der Beek - X 01 69 33 40 90 (

Y. Sidis - LLB 01 69 08 96 85

V. Brouet – LPS (coordinatrice) 01 69 15 53 34

F. Rullier Albenque - SPEC 01 69 08 75 48