Elemental tellurium is a chiral semiconductor with a small band gap of ~330  meV. Due to the natural formation of vacancies, the material is naturally p-doped. The band gap narrows under the application of hydrostatic pressure and a topological phase transition has been predicted to occur for pressures below 40 kbar [1,2]. Here, we present a pressure-dependent study of the electrical transport properties of ultra-pure elemental tellurium from 50 mK to room temperature. We find that the material undergoes the transition from an insulating state with variable range hopping (VRH) below 1.5 K to a disordered metallic state of the Anderson type.

The phase transition manifests itself in all relevant measured physical characteristics. These include a continuously vanishing T0  from the VRH, when approaching the quantum critical point (QCP), a strong linear enhancement in the low temperature conductivity in the metallic phase and a characteristic square root T dependence of the conductivity of the Anderson metal. Moreover, the magnetoresistance (MR) changes from a VRH-typical negative MR to a strong positive MR as is typical for weakly anti-localized systems.

We characterize the transition and identify the critical exponents belonging to this exotic QCP.

[1] L. A. Agapito et al., PRL 110, 176401 (2013).

[2] M. Hirayama et al., PRL 114, 206401 (2015).