Pressure-induced transformations and superconductivity of amorphous germanium

The effect of pressure on amorphous Ge was probed by Raman spectroscopy combined with molecular-dynamics simulations. A large jump occurs in the principal peak position due to nearest-neighbor Ge-Ge vibrations at 11-12 GPa and 7-5.5 GPa, respectively, during increasing/decreasing pressure due to a polyamorphic transition occurring between the low-density amorphous semiconductor and a metallic high-density polyamorph (HDA). We measured the superconducting transition temperature (Tc) using magnetic susceptibility measurements in the diamond anvil cell and determined that T c for the high-density HDA polyamorph was higher than that for the β-Sn structured Ge-II crystalline phase. © 2010 The American Physical Society