Evolution of a structural dimerization across a pressure-induced insulator-metal transition in the spin-orbit Mott insulator GaTa₄Se₈

The interplay between electronic correlations and spin-orbit coupling often gives rise to novel quantum phases of matter. When spin-orbit coupling is strong and orbital degeneracies are present, the lattice also plays an important role in determining magnetic ground states. In the Lacunar spinel GaTa₄Se₈, electronic correlations localize a single unpaired electron on tetrahedral clusters of Ta ions, while spin-orbit coupling generates J_eff=3/2 magnetic degrees of freedom. At ambient pressures and T=50 K, GaTa₄Se₈ undergoes a magnetic transition to a valence bond solid state accompanied by a structural dimerization. Hydrostatic pressures can induce an insulator to metal transition, but the evolution of magnetic correlations and the crystal structure across this transition is not known. I will present a series of low temperature, high pressure x-ray diffraction measurements following the evolution of the structural dimerization in GaTa4Se8 across the pressure-induced insulator to metal transition. These measurements shed light on the coupling of spin-orbital pseudo spins with the crystal lattice.