LORENTZ-FORCE INDEPENDENCE OF RESISTANCE TAILS IN MAGNETIC-FIELDS NEAR TC FOR THE LOW-TEMPERATURE SUPERCONDUCTOR GRANULAR NBN - A JOSEPHSON-JUNCTION MODEL

The broadened resistive transitions in a granular NbN film have been measured for field orientations both perpendicular and parallel to the current. These are essentially the same over a span of six orders of magnitude below the normal-state resistance (just above Tc) demonstrating the absence of the macroscopic Lorentz force. We show that a model of Josephson coupling between grains, rather than flux motion, can quantitatively explain the results with no adjustable parameters. Broadening of the resistive transitions of high-temperature superconductors (HTS) has also been shown to be independent of the macroscopic Lorentz force. This research demonstrates unambiguously that resistive losses near Tc and the absence of the macroscopic Lorentz force on them are not restricted to exotic HTS. © 1990 The American Physical Society.