Pressure induced superconductivity in nonlinear optical crystal ZnGeP2 and its capture at ambient pressure

An insulator could be driven into an emergent superconducting state when it is put in the extreme high-pressure condition, however, it is challenging to retain the obtained superconductivity to ambient pressure. Here we report on the creation and preservation of the superconductivity in chalcopyrite ZnGeP2, a commercial nonlinear optical crystal. Electrical transport measurements reveal that the superconductivity, induced at a critical pressure ∼17 GPa, is robust not only upon further compression to 52.9 GPa, but also in the process when the pressure is gradually released to ambient pressure. Synchrotron X-ray diffraction and Raman measurements document a structural origin of the unusual evolution of the superconductivity. The insulator-superconductor transition around 17 GPa is correlated with a structural transition from tetragonal to cubic phase, while the preserved superconductivity is consisitent with the irreversibility of the tetragonal-cubic phase transition and the presence of amorphization in the depressurized sample. These findings demonstrate a strategy to capture the high-pressure phase with emerging physical properties and will shed light on exploring novel superconductors by means of pressure treatment.