OBSERVATION OF MULTISTAGE SUPERCONDUCTING GAP STATES IN BI2SR2CACU2OX CRYSTAL-SURFACE BY LT-STM/STS

Low temperature STM/STS observation for BSCCO single crystal was carried out to investigate an intrinsic superconducting gap state of CuO2 layer. The STM observation revealed out a mid-level-layer between the top and bottom BiO surfaces of the half unit cell in the crystal c-axis direction. The STS study on this mid-level surface brought a reproducible definite superconducting gap structure which shows a finite gap region with a low conductance level of about 5%, and which also shows a nature of wide range gap parameter of Delta(max)/Delta(min) similar to 4 with Delta(min) similar to 10 meV. This definite gap structure is considered to be a more direct reflection of the superconducting electronic states of the CuO2 layer than the superconducting gap structure observed at the top BiO layer.