Muon-spin-relaxation measurements of magnetic penetration depth in organic superconductors (BEDT-TTF)2-X: X=Cu(NCS)2 and Cu

Abstract

The magnetic-field penetration depth λ in the organic superconductors κ-(BEDT-TTF) 2 Cu(NCS) 2 and κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br has been measured over a wide temperature region 20 mK≤T≤15 K via the muon-spin-relaxation technique. Linear variation of λ with T at low temperatures, found in both systems, is consistent with anisotropic superconducting pairings with line nodes in the energy gap. In the latter compound, we oberve flux depinning at T∼5 K, well below T c =12 K