Studies of boundary effects and symmetry of Cooper pairing in Bi2Sr2CaCu2Ox by LT-STS

The local density of states of quasi-particles, N(E,r), around columnar def ects generated by bombardment of high-energy heavy ions parallel to the c-a xis in Bi2Sr2CaCu2Ox (Bi-2212) and 2H-NbSe2 has been studied by scannning t unneling spectroscopy at 4.2 K and compared. The regions of columnar defect s have been found to be insulating and circular superconductor-insulator bo undaries have been studied. In Bi-2212 the N(E,r) has exhibited the increas e at E = 0 meV and the decrease at E similar to 35 meV at [110] and [(1) ov er bar 10] directions in CuO2 square network and seems to show the pattern with four-fold symmetry, while in 2H -NbSe2 such things have not been obser ved. This is new evidence of the presence of d(x2-y2) component in the orde r parameter of Bi-2212. (C) 2000 Elsevier Science B.V. All rights reserved.