The pressure-dependence of the band gap of tellurium

Elemental tellurium is a semiconductor with a small band gap of around 330 meV. Under the application of hydrostatic pressure, the band gap narrows, and it has been suggested that below its crystal phase transition at 40 kbar, the gap might close, leading to a transition into a topologically non-trivial state. Here, we present a pressure dependent study of the gap size of tellurium up to 22kbar, studied by temperature dependent electrical transport. We identify the gap size to be still well above 100 meV at our maximum pressure. Extrapolation of our data, assuming a non-linear gap narrowing (in agreement with previous studies), leaves us to assume that the gap does not close within the ambient pressure crystal phase. However, when assuming a linear narrowing of the gap, we leave a small possibility that there exists a minor pressure window at which a topological phase transition could occur. Furthermore, as the second systematic study of the gap size via transport, we see that historical inconsistencies between the measured gap size via transport and the measured optical gap size seem to be systematic and probably reflect some deeper physics of the material.