The Search for Topological States and Anomalous Electronic Behaviors in In- and Mn-doped GeTe

Abstract

Recently, researchers predicted and showed experimentally that GeTe exhibits novel physics, such as the giant Rashba effect, so the potential of this semiconductor to exhibit additional novel physics phenomena, such as topological electronic states, motivates a resurgence in its study. Due to its consistently metallic and strong p-type behavior, however, it is very difficult to observe electronic states that may lie above the Fermi level. Here, I report and describe a series of single crystal samples that I grew by a modified Bridgman technique in both the Ge1-xInxTe and (GeTe)1-x(In2/3Te)x systems, in which I found anomalous highly insulating behavior at 14 at. % In content in the normally highly metallic and conducting GeTe system. Additionally, I report my characterization of a series of In- and Mn-co-doped GeTe crystals that show ferromagnetic behavior with increasing Curie temperature as a function of increasing Mn content as well as an anomalous Hall effect. While I have not yet gathered direct evidence for topological electronic states in these two systems, I have found anomalous behaviors in doped GeTe and, as a result, have laid the groundwork for future study that may lead to the discovery and characterization of additional novel physics phenomena in doped GeTe.