Tunneling measurement for the energy gap in quaternary compound superconductors YNi2B2C, LuNi2B2C and YBCO by LTSTM

초록

Tunneling spectra of a single crystalline YNi2B2C (Tc = 15.4 K), LuNi2B2C (Tc= 15.7 K) and YBCO (Tc = 90 K) have been measured by a point contact spectroscopy using a low temperature scanning tunneling microscope. The conductance curve of RNi2B2C shows a smeared gap structure 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-axis oriented YBCO films shows periodic current steps at the corresponding voltage of V = (2n+1)V0. Voltage period ΔV shows a dependence on the sample-to-tip distance implying the single electron tunneling nature.