Ultrastable Amorphous Sb₂Se₃ and Its Density-Driven Superconductivity

Chalcogenide glasses have been considered as a promising semiconductor in photovoltaic applications. The metastable nature limits its application condition, thus searching for ultrastable glass formation condition has attracted much effort. Here we report an enhancement in thermal stability by 17K comparing to ordinary formation condition in Sb2Se3 by optimizing the substrate temperature during the thermal evaporation process. Ultrastable amorphous Sb2Se3 showed the smallest surface roughness and highest refractive index. By in situ high temperature-high energy synchrotron X-ray diffraction, the difference in structure relaxation between ordinary and ultrastable amorphous Sb2Se3 was manifested by local structure evolution. Upon compression, amorphous Sb₂Se₃ undergoes a LDA to HAD transition at 24 GPa, defined as the amorphous density surpassing the crystal counterpart, and the superconductivity emerges. The superconducting critical temperature is enhanced when pressure induced crystallization at 51 GPa. HDA phase, featured by metavalent bonding, plays a pivotal role in the delocalization of electrons and the occurrence of superconductivity in the amorphous state. The results presented here provide a structural basis for the incipient structure of pressure-induced superconductivity in amorphous solids.