Andreev Bound States at the Onset of Phase Coherence in Bi(2)Sr(2)CaCu(2)O(8)

Phys Rev Lett. 2002 Oct 21;89(17):177001. doi: 10.1103/PhysRevLett.89.177001. Epub 2002 Oct 3.

Abstract

A new technique of planar tunneling spectroscopy has been developed to access the in-plane density of states of optimally doped Bi(2)Sr(2)CaCu(2)O(8) single crystals. The low energy spectrum is observed to depend on crystallographic orientation. When tunnel current is injected nominally along the Cu-Cu bond direction, a zero-bias conductance peak is observed to appear simultaneously with the onset of bulk superconductivity. These data demonstrate the existence of surface-induced states in this system and confirm the d-wave symmetry of the superconducting order parameter.