Fermi level position, Coulomb gap, and Dresselhaus splitting in (Ga,Mn)As

TL;DR

This study uses angle-resolved photoemission to explore the electronic structure of (Ga,Mn)As, revealing the Fermi level position, Coulomb gap effects, and Dresselhaus spin-orbit splitting, with implications for spintronic device functionalities.

Contribution

It provides the first direct measurement of the Fermi level position, Coulomb gap characteristics, and Dresselhaus splitting in (Ga,Mn)As, linking electronic structure to magnetic and spin-orbit phenomena.

Findings

Fermi level is within the heavy/light hole band.

Coulomb gap width and depth increase as Curie temperature decreases.

Linear magnetic dichroism indicates Dresselhaus spin-orbit coupling.

Abstract

Carrier-induced nature of ferromagnetism in a ferromagnetic semiconductor, (Ga,Mn)As, offers a great opportunity to observe novel spin-related phenomena as well as to demonstrate new functionalities of spintronic devices. Here, we report on low-temperature angle-resolved photoemission studies of the valence band in this model compound. By a direct determination of the distance of the split-off band to the Fermi energy EF, we conclude that EF is located within the heavy/light hole band. However, the bands are strongly perturbed by disorder and disorder-induced carrier correlations that lead to the Coulomb gap at EF, which we resolve experimentally in a series of samples, and show that its depth and width enlarge when the Curie temperature decreases. Furthermore, we have detected surprising linear magnetic dichroism in photoemission spectra of the split-off band. By a quantitative theoretical analysis we demonstrate that it arises from the Dresselhaus-type spin-orbit term in zinc-blende crystals. The spectroscopic access to the magnitude of such asymmetric part of spin-orbit coupling is worthwhile, as they account for spin-orbit torque in spintronic devices of ferromagnets without inversion symmetry.