Magnetotransport in Ultrathin 2-D Superconducting Mo2C Crystals

Ultrathin transition metal carbides are a class of emerging 2-D materials with many intriguing properties and applications. Here, we report the transport measurements on high-quality ultrathin Mo2C crystals, which are synthesized by a chemical vapor deposition method. We demonstrate 2-D nature of the observed superconductivity in ultrathin Mo
₂
C crystals, being consistent with a Berezinskii-Kosterlitz-Thouless transition. As the sample thickness decreases, the Mo
₂
C crystals exhibit negative magnetoresistance behavior at low magnetic fields deep in the superconducting state. We attribute these results to strong phase fluctuations of the superconducting order parameters near the superconductor-insulator transition. Our results demonstrate that these high-quality ultrathin Mo
₂
C crystals provide an appealing platform to gain insights into 2-D superconductivity in a clean system.