Effects of pressure and magnetic field on superconductivity in ZrTe3: Local pair-induced superconductivity

Abstract

In this work, the origin of the highly anisotropic superconducting transition in ZrTe3, where the resistance along the a axis, R a, is reduced at 4 K but those along the b axis, R b, and axis, R c′, are reduced at 2 K, was explored with the application of a magnetic field and pressure by the electrical resistance measurements. We found that the behavior of the upper critical field and its anisotropy as well as the pressure dependence determined by the R a measurements are quite similar to those of R b. Moreover, the excess conductivity for R b indicates anomalous behavior. These results support an unconventional origin for the anisotropic transition rather than conventional superconducting fluctuation. The reduction in R a is due to filamentary superconductivity (SC) induced by locally bound electron pairs (local pairs), which correspond to bi-polarons, and the transition of R b corresponds to the emergence of bulk SC originating from the Cooper pairs triggered by the transfer of the local pairs.