First order transition from correlated electron semiconductor to ferromagnetic metal in single crystalline FeSi1-xGex

TL;DR

This study reveals a first-order transition in FeSi1-xGex from a correlated electron semiconductor to a ferromagnetic metal at a critical Ge concentration, highlighting the interplay of correlations and disorder.

Contribution

It provides the first detailed phase diagram of FeSi1-xGex showing a correlation-induced insulator-metal transition with experimental evidence from single crystals.

Findings

Transition occurs at x ~ 0.25

Insulating gap decreases with Ge doping

Specific heat tracks Kondo insulator density of states

Abstract

The phase diagram of FeSi1-xGex, obtained from magnetic, thermal and transport measurements on single crystals, shows a first-order transition from a correlated electron semiconductor to a ferromagnetic metal at a critical concentration, x ~ 0.25. The gap of the insulating phase strongly decreases with x. The specific heat coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with a correlation induced insulator-metal transition in conjunction with disorder on the Si/Ge ligand site.