The mechanism behind SnO metallization under high pressure

SnO is known to undergo metallization at similar to 5 GPa while retaining its tetragonal symmetry. However, the mechanism of this metallization remains speculative. We present a combined experimental and computational study including pressure-dependent infrared spectroscopy, resistivity, and neutron powder diffraction measurements. We show that, while the excess charge mobility increases with pressure, the lattice distortion, in terms of the z-position of Sn, is reduced. Both processes follow a similar trend that consists of two stages, a moderate increment up to similar to 3 GPa followed by a rapid increase at higher pressure. This behavior is discussed in terms of polaron delocalization. The pressure-induced delocalization is dictated by the electron-phonon coupling and related local anisotropic lattice distortion at the polaron site. We show that these polaronic states are stable at 0 GPa with a binding energy of similar to 0.35 eV. Upon increasing the pressure, the polaron binding energy is reduced with the electron-phonon coupling strength of Gamma and M modes, enabling the electrical phase transition to occur at similar to 3.8 GPa. Further compression increases the total electron-phonon coupling strength up to a maximum at 10 GPa, which is a strong evidence of dome-shaped superconductivity transition with T-c = 1.67 K.

Automated summary

This study investigates the metallization mechanism of SnO under high pressure using combined experimental and computational methods. It is found that pressure induces polaron delocalization, with electron-phonon coupling and lattice distortion being key factors. Additionally, the pressure-induced charge transition and dome-shaped superconductivity transition are observed.