Temperature dependence of the energy band gap in ZrTe5: Implications for the topological phase

Using Landau level spectroscopy, we determine the temperature dependence of the energy band gap in zirconium pentatelluride (ZrTe₅). We find that the band gap reaches E_g = (5±1) meV at low temperatures and increases monotonously when the temperature is raised. So this implies that ZrTe₅ is a weak topological insulator, with non-inverted ordering of electronic bands in the center of the Brillouin zone. Our magneto-transport experiments performed in parallel show that the resistivity anomaly in ZrTe₅ is not connected with the temperature dependence of the band gap.