Pressure-induced superconductivity in triangular lattice spin liquid candidate NaYbSe<sub>2</sub>

Abstract

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-<i>T</i><sub>c</sub> superconductor, by using pressure or chemical doping. Rear-earth chalcogenides NaYbCh<sub>2</sub> (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 NaYbCh<sub>2</sub> (Ch = O, S, Se) under high pressures. For NaYbSe<sub>2</sub>, zero-resistance behavior is observed at 26.9 GPa, showing that the superconductivity comes into being. The superconducting transition temperature (<i>T</i><sub>c</sub>) is around 5.6 K at 26.9 GPa and robust against pressure till 45 GPa. The phase diagram of <i>T</i><sub>c</sub> versus pressure for NaYbSe<sub>2</sub> is constructed. For NaYbS<sub>2</sub>, the room temperature resistance decreases from the order of 10<sup>11</sup> Ω at 10 GPa to 10 Ω at 67 GPa. However, neither superconductivity nor insulator-metal transition is observed. Additionally, the NaYbO<sub>2</sub> keeps insulating and the resistance is too large to be detected in a pressure range of 0–60 GPa.