Charge density wave transition and superconductivity in 2H-NbSe2. Direct measurement of the penetration depth in a layered superconductor

Abstract

The Schawlow-Devlin self-inductance method of direct measurement of the penetration depth has been adopted for layered superconductors, for which this method is especially suitable because the calibration procedure is very simple for them. The ratio of coherence length to mean free path xi/sub 0//l within the layer is deduced from the penetration depth measured by the new method and the resistivity, and is found to be 0.14 for a pure crystal of 2H-NbSe/sub 2/ with RRR of about 50. The effect of the CDW transition on the superconductivity in 2H-NbSe/sub 2/ is investigated through the measurement of the penetration depth. In addition to pure crystals, some modified crystals are investigated where the CDW transition is suppressed. The London penetration depth lambda/sub L/(0) as well as the superconducting transition temperature T/sub c/ show a slight but apparent increase with decreasing CDW transition temperature T/sub D/ of the samples. Both behaviors may be explained by a decrease in the reduction of N(E/sub f/) due to the suppression of the CDW transitions, where N(E/sub F/) is the density of states at the Fermi energy. The result also suggests a systematic increase of the ratio of effective mass to electron density m/sub parallel//n ofmore » the electron system with the suppression of the CDW transition.« less