Normal and superconducting state properties of Cu-doped FeSe single crystals

We report the evolution of the physical properties of FeSe single crystals with Cu substitution. We show that introducing Cu suppresses bulk superconductivity quickly, much faster than the decrease in structural transition temperature, and further doping Cu induces a metal-insulator transition. In contrast, zero-field ab-plane resistivity rho(xx) exhibits an unusual temperature dependence rho(xx) (T) similar to AT(n), with n similar to 1, that is almost unchanged with the variation of Cu content. This result implies that magnetic fluctuations in FeSe are insensitive to the Cu substitution. The field dependence of the Hall resistivity of Fe1-xCuxSe with x > 0 shows a positive slope in the low-temperature region which can be ascribed to the relatively higher hole mobility than the electron one. Therefore, the low-concentration Cu dopant as a strong scattering source can lead to the significant decrease in electron mobility which is detrimental to superconductivity, but it has minor effects on the carrier densities of electrons and holes as well as the shapes of the Fermi surfaces. Correspondingly, the structural transition and magnetic fluctuations in Fe1-xCuxSe change slowly with x.

Automated summary

The introduction of Cu quickly suppresses superconductivity in FeSe single crystals, induces a metal-insulator transition, and has minor effects on magnetic fluctuations. Additionally, Cu doping significantly decreases electron mobility, which is detrimental to superconductivity.