Muon-Spin Rotation Measurements of the Magnetic Field Dependence of the Vortex-Core Radius and Magnetic Penetration Depth in NbSe2

Muon-spin rotation spectroscopy (μSR) has been used to measure the internal magnetic field distribution in NbSe2 for Hc1≪H<0.25Hc2. The deduced profiles of the supercurrent density Js indicate that the vortex-core radius ρ0 in the bulk decreases sharply with increasing magnetic field. This effect, which is attributed to increased vortex-vortex interactions, does not agree with the dirty-limit microscopic theory. A simple phenomenological equation in which ρ0 depends on the intervortex spacing is used to model this behavior. In addition, we find for the first time that the in-plane magnetic penetration depth λab increases linearly with H in the vortex state of a conventional superconductor.