Pressure-induced reentrant metallic phase in lithium

We report the metal (0--80 GPa)--semiconductor ($oC$40, 80--120 GPa)--metal ($oC$24, >120 GPa) transitions of lithium under compression, as observed through simultaneous electrical resistance and x-ray diffraction measurements. The energy gap in the $oC$40 semiconductor quickly decreases with applied pressure, and Li reverts back to a metallic state accompanied by a structural transition to $oC$24. The large ρ value for $oC$24 indicates that this re-entrant metallic phase is a so-called ``poor metal.'' Our results reveal a characteristic phase diagram that demonstrates the existence of a semiconductor phase between two distinct metallic phases.