Pressure-Induced Metallization and Structural Phase Transition in the Quasi-One-Dimensional TlFeSe_2

We report a comprehensive high-pressure study on the monoclinic TlFeSe_2 single crystal, which is an antiferromagnetic insulator with quasi-one-dimensional crystal structure at ambient pressure. It is found that TlFeSe_2 undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above P_\rm c \approx 13 GPa, accompanied with a large volume collapse of \Delta V/V_0=8.3\%. In the low-pressure monoclinic phase, the insulating state is easily metallized at pressures above 2 GPa; while possible superconductivity with T_\rm c^\rm onset \sim 2 K is found to emerge above 30 GPa in the high-pressure phase. Such a great tunability of TlFeSe_2 under pressure indicates that the ternary AFeSe_2 system (A = Tl, K, Cs, Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition, dimensionality crossover, and superconductivity.