MgB2 grain boundary nanobridges prepared by focused ion beam

Abstract

We have fabricated MgB2 grain boundary nanobridges by focused-ion-beam etch and studied their transport properties. Nanobridges with a nominal width and length of 100 nm were patterned across naturally formed single grain boundaries in the microbridges, which were prepatterned by a standard argon ion milling technique. We have studied current-voltage (I-V) characteristics, the temperature-dependent critical current, and the normal-state resistance. The measured properties were interpreted based on a flux flow model. In the I-V curves, a typical resistively shunted-junction characteristic was observed near T-c, however, as temperature decreases, flux-flow behavior became dominant, in accordance with the crossover of the ratio of the bridge length to the coherence length from the single-phased regime to the flux-flow regime. The temperature-dependent critical current was I-c(T) similar to (1-T/T-c)(1-1.5), similar to that of a superconducting film. The normal-state resistance increased steeply as temperature approaches T-c, in agreement with the flux-flow theory. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3063688]