Spin-orbit coupling and quantum interference effects in the transport properties of tellurium

Elemental tellurium in bulk is a small band gap semiconductor with a unique crystal structure, consisting of atomic helices, arranged in a hexagonal lattice. The implicit chirality of tellurium single crystals, the anisotropy of the lattice and a strong spin-orbit coupling render elemental tellurium an extraordinarily interesting material for possible applications. At the same time, the fundamental physical properties, as well as its ground state, are particularly interesting due to its unique spin polarization and the possible existence of topologically non-trivial phases. Recently, several groups have predicted a topological phase transition below 20kbar and some experiments have been interpreted in favor of these predictions.
In the first part of the talk, I will present pressure-dependent transport and magnetotransport measurements, which have been performed on high quality tellurium single crystals [1]. We clearly show that the observed phase transition exists, but it cannot be interpreted as a topological phase transition from a semiconducting to a topologically interesting state. Instead, we show that the quantum phase transition is of the Anderson-Mott manifold. The Anderson-localization occurs due to the natural existence of vacancies in Te single crystals and all measured physical quantities show the typical critical behavior as is generally expected from such a transition. The misunderstanding of data from previous measurements is a consequence of the fact that the transition is induced by a pressure-induced band-bending, which leads to a pseudo-Lifshitz transition, dressed by the Anderson insulating state, at around 17kbar.
In the second part of the talk, I will present an extensive study of the magnetoconductive behavior of chemically doped tellurium single crystals. For certain current and field-directions, we observe an extraordinarily strong anomalous hall effect, which is related to a relevant asymmetrical component in the transvers magnetoresistance. This phenomenon has been reported for other materials which similar electromagnetic properties. We analyze our results comparing the chirality and geometric structure of different crystals. Specifically, our data indicates that doped tellurium has many features in common with Weyl-metals, as the unique spin texture of tellurium’s valence band resembles that of certain Weyl metals.