Zero-Bias-Conductance-Peak Anomaly of Ta-I-Al Tunnel Junctions at 0.3 K and 90 kG

We have studied the zero-bias-conductance-peak anomaly in a Ta-$I$-Al tunnel junction over a magnetic field range of 1 to 90 kG at a temperature of 0.3 K, and have made a detailed comparison between experiment and the $s-d$ exchange theory of electron tunneling. Good agreement between theory and experiment was obtained for the line shape of the conductance peak and its zero-bias temperature dependence. The line shape of the conductance curves found experimentally at high magnetic fields agreed reasonably well with the theory if magnetic-field-induced lifetime broadening was included. There was, however, a serious discrepancy between theory and experiment for the zero-bias magnetoresistance.