A-B PLANE TUNNELING SPECTROSCOPY AND INPLANE GAP ANISOTROPY IN BI2SR2CACU2O8

The quality of the tunneling spectroscopy of Bi2Sr2CaCu2O8 can be impr oved significantly by tunneling into the edge of a single crystal, as opposed to directly into a cleaved face. This junction geometry allows tunneling exclusively in the a-b plane, and we will. discuss some fea tures that can be reproduced consistently with this technique. This ex perimental approach also provides us a unique opportunity to observe t he gap anisotropy within the a-b plane. We find that the energy gap (D elta(ab)) varies from 20 meV to 40 meV, with the maximum value along t he orthorhombic crystal axes and the minimum value along the Cu-O bond direction. No nodal line has been observed, possibly due to the limit ation in angular resolution of the tunneling technique.