Ground State Study of Quantum Material GaTa₄Se₈

The quantum material GaTa₄Se₈ has attracted a substantial amount of attention because it exhibits a variety of interesting physical properties, such as metallization, J_eff quantum state, and topological superconductivity, and moreover, it is a medium for resistive switch and electric storage. However, controversies still exist on its insulating ground state, which hinders from understanding its various physical properties. The insulating ground state of GaTa₄Se₈ has been considered over a long period of time as a cubic symmetric structure with space group $F\bar{4}3m$, and as a Mott-type energy gap driven by the combination of the spin-orbit coupling and the electronic correlation interaction. However, recent first-principles phonon calculations have shown that the cubic structure is mechanically unstable due to the presence of imaginary frequencies, and have predicted to be stabilized into the trigonal structure ($R3m$) or the tetragonal structure ($F\bar{4}{2}_{1}m$) through lattice distortion. In order to further investigate the ground state structure of GaTa₄Se₈, here we combine multiple experimental techniques such as Raman spectroscopy, X-ray diffraction, and resistance measurement to adjust its energy gap by pressure, and compare the experimental results with first-principles calculations. Our results show that the trigonal symmetric structure ($R3m$) is more consistent with our experimental observations.