STM Spectroscopy on Partially Deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br

We report the electron tunneling spectroscopy on κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br using a low temperature STM. Protonated d[0,0] and partially deuterated d[2,2] salts were studied. In both salts, the functional shape of the tunneling differential conductance curve in the superconducting state is explained by the d-wave pairing symmetry. We obtain the gap parameter Δ as 2.1-3.9 and 3.0-4.8 meV for d[0,0] and d[2,2] salt, respectively. The value of 2Δ/kT c in d[2,2] salt is slightly larger than that in d[0,0] salt. The pseudogap is observed below about 50 K in both salts.