P. Samuely, S. I. Vedeneev, A. G. M. Jansen, I. P. Kazakov, and R. Gonnelli, Tunneling into the BiSrCuO superconductor up to the critical magnetic field, Low Temp. Phys. 18, (1992) [Fiz. Nizk. Temp. 18, 621-622, (1992)].