TUNNELING MEASUREMENT FOR THE ENERGY-GAP IN QUATERNARY COMPOUND SUPERCONDUCTORS YNI2B2C, LUNI2B2C AND YBCO BY LTSTM

Tunneling spectra of a single crystalline YNi2B2C (T-c = 15.4 K), LuNi 2B2C (T-c = 15.7 K) and YBCO (T-c = 90 K) have been measured by a poin t contact spectroscopy using a low temperature scanning tunneling micr oscope. The conductance curve of RNi(2)B(2)C shows a smeared gap struc ture with an almost linear density of states inside of the gap region. The linear conductance inside the gap region has been explained by a proximity induced energy gap in the degraded surface normal layer. c-a xis oriented YBCO films shows periodic current steps at the correspond ing voltage of V = (2n+1)V-0. Voltage period Delta V shows a dependenc e on the sample-to-tip distance implying the single electron tunneling nature.