  Layered transition-metal tellurides have attracted considerable attention
because of their rich physics; for example, tungsten ditelluride WTe2 exhibits
extremely large magnetoresistance; the tritelluride ZrTe3 shows a charge
density wave transition at low temperature; and the pentatelluride ZrTe5
displays an enigmatic resistivity anomaly and large thermoelectric power.
Recently some transition-metal tellurides are predicted to be quantum spin Hall
insulators (e.g. ZrTe5 and HfTe5) or Weyl semimetals (e.g. WTe2 and MoTe2) and
were subjected to intensive investigations. Here, we report on the discovery of
superconductivity in hafnium pentatelluride HfTe5 under high pressure. We
observe two structural phase transitions and metallization with
superconductivity developing at around 5 GPa. A maximal critical temperature of
4.8 K is attained at a pressure of 20 GPa, and superconductivity persists up to
the maximum pressure in our study (42 GPa). Theoretical calculations indicate
that the superconductivity develops mainly in the Te atom layers at medium
pressure and in the Te atom chains at high pressure.
