INFLUENCE OF ELECTROMAGNETIC ENVIRONMENT ON TUNNELING CURRENT THROUGHNORMAL METAL-SUPERCONDUCTOR JUNCTIONS

Based on a tunneling Hamiltonian model, the two-electron tunneling cur rent through normal metal-superconductor junctions is studied by incor porating the influence of a dissipative electromagnetic environment wi th an Ohmic resistor R. We show that at low bias voltages the two-elec tron tunneling current displays a power-law behavior as I proportional to V-4g+1, where g=e(2)R/pi h at zero temperature due to electromagne tic fluctuations. This suggests that suppression of the two-electron t unneling current is more remarkable compared with the usual tunneling current in normal junctions where I proportional to V-g+1.