Structural, vibrational and electrical properties of type-II Dirac semimetal PtSe under high pressure.

We present a high-pressure study of type-II Dirac semimetal PtSe single crystals through synchrotron x-ray diffraction (XRD), electrical transport and Raman scattering measurements in diamond anvil cells with pressures up to 36.1-42.3 GPa, from which two critical pressure points associated with unusual electron-phonon coupling are unraveled. We show that both resistance and phonon linewidth of Raman modes display anomalies at the first critical pressure of P ~ 10 GPa, in accordance with a scenario of pressure-induced disappearance/appearance of type-II/type-I Dirac points around P predicted previously. The second critical pressure P ~ 20 GPa may correspond to a structural crossover of PtSe from quasi-2D lattice to 3D network, which is revealed via detailed analysis of the structural parameters extracted from XRD refinement, Raman modes shifts as well as parameters from fitting of the low-temperature resistance. Our results demonstrate great tunability of PtSe via strain engineering, thanks to the single p-orbital manifold derived electronic states that are susceptible to out-of-plane and in-plane distances.