  Here we report the discovery of superconductivity in multiple phases of the
compressed GeSb2Te4 (GST) phase change memory alloy, which has attracted
considerable attention for the last decade due to its unusual physical
properties with many potential applications. Superconductivity is observed
through electrical transport measurements, both for the amorphous (a-GST) and
for the crystalline (c-GST) phases. The superconducting critical temperature,
TC, continuously increases with the applied pressure reaching a maximum Tc =6K
at P=20 GPa for a-GST, whereas the critical temperature of the cubic phase
reaches a maximum Tc =8 K at 30 GPa. This new material system, exhibiting a
superconductor-insulator quantum phase transition (SIT) has an advantage over
disordered metals since it has a continuous control of the crystal structure
and the electronic properties using pressure as an external stimulus, which was
lacking in SIT studies until today.
