Recent discoveries of two-dimensional (2D) crystalline superconductors [1] have led to clarifications of various intrinsic nature in magnetic fields. For example, 2D crystalline superconductors with weak pinning are very fragile against out-of-plane magnetic fields, and thus show a quantum metallic state due to quantum fluctuations [2] (though this phenomenon is still under debate [3]). However, there has been no report for how the BKT state at zero magnetic field evolves into the normal state through the dynamic states with increasing current in such systems. In this talk, we report on transport properties at zero magnetic field in ion-gated MoS₂ as a function of current and temperature. We show a clear BKT transition and anomalous kinks observed in resistance-temperature and current-voltage curves, and discuss the dynamic phase diagram based on these data, which contains a variety of current-induced nonequilibrium states originating from not only thermal but also quantum dissociation of vortices and antivortices.
[1] Y Saito et al. Nature Rev. Mat. 2 16094 (2016), [2] Y. Saito et al. Science 350, 409 (2015). A. W. Tsen, Nature Phys. 12, 208 (2016), [3] I. Tamir et al. arXiv: 1804.04648