Weak link grain boundaries in intermetallic superconductors

Abstract Studies of rf-SQUID effect in ternary (YRuB 2 , LuRuB 2 , LaRu 3 Si 2 ) and in binary V 3 Si intermetallic bulk superconductors have been carried out for investigating the nature of grain boundaries in these superconductors. YRuB 2 ( T c ∼7.5 K), LuRuB 2 ( T c ∼10 K) and LaRu 3 Si 2 ( T c ∼7 K) ternary superconductors are found to show rf-SQUID voltage–flux modulations from 4.2 K to close to T c . This indicates that the natural grain boundaries in the ternary intermetallic superconductors behave as Josephson weak links. Rf-SQUID effect is not observed in V 3 Si binary superconductors, which indicates that the grain boundaries in V 3 Si are not weak link type. STM/STS studies of the YRuB 2 and V 3 Si grain boundaries (GB) are also reported. The interior of the GB in YRuB 2 is found to be of quasi-insulating type and thus provides a weak link effect. On the contrary the interior regions of the GB of V 3 Si is found to be of metallic type and thus provides proximity coupling between the grains of V 3 Si.