Pressure-induced superconductivity in triangular lattice spin liquid candidate NaYbSe2

Quantum spin liquid is an exotic state without magnetic order down to zero-temperature due to spin frustration, which is closely related to high temperature superconductivity. Therefore, an important issue arises whether the quantum spin liquid can be adjusted into a superconductor, even high-Tc superconductor, by using pressure or chemical doping. Rear-earth chalcogenides NaYbCh2 (Ch = O, S, Se), consisting of planar triangular lattice, exhibit no long-range magnetic order down to the lowest measured temperatures in specific heat, nuclear magnetic resonance, and neutron scattering, and are considered as a quantum spin liquid candidate. Here we investigate the electrical transport properties of NaYbCh2 (Ch = O, S, Se) under high pressures. For NaYbSe2, zero-resistance behavior is observed at 26.9 GPa, showing that the superconductivity comes into being. The superconducting transition temperature (Tc) is around 5.6 K at 26.9 GPa and robust against pressure till 45 GPa. The phase diagram of Tc versus pressure for NaYbSe2 is constructed. For NaYbS2, the room temperature resistance decreases from the order of 1011 W at 10 GPa to 10 W at 67 GPa. However, neither superconductivity nor insulator-metal transition is observed. Additionally, the NaYbO2 keeps insulating and the resistance is too large to be detected in a pressure range of 0-60 GPa.