Variation of the density of states in amorphous GdSi at the metal-insulator transition

TL;DR

This study investigates how the density of states in amorphous GdSi changes near the metal-insulator transition under magnetic fields, revealing a gradual evolution from insulating to metallic electronic characteristics.

Contribution

It provides detailed measurements of conductivity and tunneling conductance to characterize the density of states evolution across the transition in amorphous GdSi.

Findings

Conductivity increases linearly with magnetic field near the transition.

Density of states at the Fermi level remains zero at low fields despite metallic conductivity.

The energy dependence of the density of states evolves from a soft gap to metallic behavior.

Abstract

We performed detailed conductivity and tunneling mesurements on the amorphous, magnetically doped material $\alpha$-Gd$_x$Si$_{1-x}$ (GdSi), which can be driven through the metal-insulator transition by the application of an external magnetic field. Conductivity increases linearly with field near the transition and slightly slower on the metallic side. The tunneling conductance, proportional to the density of states $N(E)$, undergoes a gradual change with increasing field, from insulating, showing a soft gap at low bias, with a slightly weaker than parabolic energy dependence, i.e. $N(E) \sim E^c$, $c \lesssim 2$, towards metallic behavior, with $E^d$, $0.5 \lt d \lt 1$ energy dependence. The density of states at the Fermi level appears to be zero at low fields, as in an insulator, while the sample shows already small, but metal-like conductivity. We suggest a possible explanation to the observed effect.