Metal - Insulator transition in Fe1.01-xCuxSe

TL;DR

This study explores how copper substitution in Fe1.01Se induces a metal-insulator transition, introduces magnetic moments, and suppresses superconductivity, revealing complex phase changes in the material.

Contribution

It demonstrates the effects of copper doping on Fe1.01Se, including the suppression of superconductivity and the emergence of magnetic and insulating phases, which were not previously characterized.

Findings

Copper substitution suppresses superconductivity at 1.5% doping.

A metal-insulator transition occurs at 4% copper doping.

Magnetic moments and spin-glass behavior emerge near 12% doping.

Abstract

Iron Selenide, Fe1.01Se, the layered parent compound of the recently discovered superconducting arsenide family, has previously been shown to be non magnetic and superconducting with a critical temperature of 8 K. Here we show that copper can be substituted at the iron site in Fe1.01Se up to a solubility limit of 20-30 %, after which a first order transition to the three-dimensional CuFeSe2 structure type is observed. As little as 1.5 % percent copper is sufficient to suppress the superconductivity, and 4 % drives the system through a metal-insulator transition. A local magnetic moment is introduced, which maximizes near 12% doping, where a spin-glass transition near 15 K is observed.