Characteristic inter-grain superconducting transition in quasi-one-dimensional sulfide AV6S8 (A=In, Tl)

The superconducting phase transitions of quasi-one-dimensional compound (V6S8, InV6S8, TlV6S8) were studied by the measurement of AC magnetic susceptibility χ′. In the sintered sample, the χ′ began to decrease monotonously at TC1. On the other hand, the χ′ of powdered sample decreased stepwise, and was characterized by two transition temperatures TC1 and TC2 (TC1>TC2). Under the magnetic field, TC2 shifted to the lower temperature, while the shift of TC1 was negligibly small. The TC1 is considered to be the transition temperature in the grains, and TC2 is the inter-grain transition temperature.