Recently emerging two-dimensional (2D) superconductors in atomically thin layers and at heterogeneous interfaces are attracting growing interest in condensed matter physics. Here, we report that ion-gated ZrNCl surface, exhibiting a dome-shaped phase diagram with a maximum critical temperature of 14.8 kelvin, behaves as a superconductor persisting to the 2D limit. The superconducting thickness estimated from the upper critical fields is ~ 1.8 nanometers, which is thinner than one-unit-cell. The majority of the vortex phase diagram down to 2 kelvin is occupied by a metallic state with a finite resistance, owing to the quantum creep of vortices caused by extremely weak pinning and diminishing disorder. Our findings highlight the potential of electric-field-induced superconductivity, establishing a new platform for accessing quantum phases in clean 2D superconductors.
@article{arxiv.1511.03266,
title = {Metallic ground state in an ion-gated two-dimensional superconductor},
author = {Yu Saito and Yuichi Kasahara and Jianting Ye and Yoshihiro Iwasa and Tsutomu Nojima},
journal= {arXiv preprint arXiv:1511.03266},
year = {2015}
}