Observation of a semimetal–semiconductor phase transition in the intermetallic ZrTe5

Temperature dependent high-resolution angle-resolved photoelectron spectroscopy has been performed on the quasi-two-dimensional compound ZrTe 5 , a metal at low temperatures ( K) that exhibits a maximum resistivity at a temperature ( T c ), concomitant with a sign change of the thermopower. A semiconducting gap has been observed in the photoemission spectra, where the valence band maximum shifts upward from 82 meV (75 K) to 40 meV (170 K) as a function of temperature. The band shifts are accompanied by small band distortions. Based on the photoemission experiments, in conjunction with the metallic character of ZrTe 5 at low temperatures, we have modelled the thermopower of ZrTe 5 by treating it as a metal at low temperatures and a semiconductor at elevated temperatures.