Superconducting and normal-state gaps in kappa-(BEDT-TTF)(2)Cu(NCS)(2) studied by STM spectroscopy

Scanning tunneling microscope (STM) spectroscopy on the b-c plane of single crystals of an organic superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) has been performed in superconducting and normal states with varying temperature. The temperature dependence of the zero-bias conductance dI/dV\(V=0) is well explained by the d-wave gap model considering the T-2 dependence of the broadening parameter of the one-electron level Gamma (T), which is obtained from the fitting of the dI/dV-V curves to the d-wave Sap model. The dI/dV-V curve shows a broad dip around the Fermi energy above T-c = 10.4 K. This pseudogap structure remains up to about 45 K. The magnitude of the pseudogap is much larger than that of the superconducting gap Delta (p) similar to 3 meV. (C) 2000 Elsevier Science Ltd. All rights reserved.