Anomalous field dependence of the vortex-core radius and magnetic penetration depth in YNi2B2C probed by μSR

Muon spin rotation measurements were performed to deduce the magnetic penetratioin depth lambda and vortex core radius rho(v) in the mixed state of YNi2B2C for H-c1 much less than H less than or equal to 0.7 H-c2. A preliminary analysis based on the modified London model shows that rho(v) decreases steeply with increasing H, while lambda increases linearly in H. (C) 2000 Elsevier Science B.V. All rights reserved.