Pressure induced structural, electronic topological, and semiconductor to metal transition in AgBiSe2.

We report the effect of strong spin orbit coupling inducing electronic topological and semiconductor to metal transitions on the thermoelectric material AgBiSe₂ at high pressures. The synchrotron X-ray diffraction and the Raman scattering measurement provide evidence for a pressure induced structural transition from hexagonal (α-AgBiSe₂) to rhombohedral (β-AgBiSe₂) at a relatively very low pressure of around 0.7GPa. The sudden drop in the electrical resistivity and clear anomalous changes in the Raman line width of the A_1g and E_g ⁽¹⁾ modes around 2.8GPa was observed suggesting a pressure induced electronic topological transition. On further increasing the pressure, anomalous pressure dependence of phonon (A_1g and E_g ⁽¹⁾) frequencies and line widths along with the observed temperature dependent electrical resistivity show a pressure induced semiconductor to metal transition above 7.0GPa in β-AgBiSe₂. First principles theoretical calculations reveal that the metallic character of β-AgBiSe₂ is induced mainly due to redistributions of the density of states (p orbitals of Bi and Se) near to the Fermi level. Based on its pressure induced multiple electronic transitions, we propose that AgBiSe₂ is a potential candidate for the good thermoelectric performance and pressure switches at high pressure. [ABSTRACT FROM AUTHOR]