We present high-precision measurements of the penetration depth of single crystals of k-(ET)2 Cu[N(CN)2]Br and k-(ET)2 Cu(NCS)2at temperatures down to 0.4 K. We find that, at low temperatures, the in-plane penetration depth (λ||)varies as a fractional power law, λ|| ∼T3/2. While this may be taken as evidence for novel pair excitation processes, we show that the data are also consistent with a quasilinear variation of the superfluid density, as is expected for a d-wave superconductor with impurities or a small residual gap. Our data for the interplane penetration depth show similar features and give a direct measurement of the absolute value, λ⊥(0)=100 ±20 μm.
ASJC Scopus subject areas
- Physics and Astronomy(all)