High Phase Purity of Large-Sized 1T'-MoS2 Monolayers with 2D Superconductivity.

The development of transition metal dichalcogenides has greatly accelerated research in the 2D realm, especially for layered MoS2 . Crucially, the metallic MoS2 monolayer is an ideal platform in which novel topological electronic states can emerge and also exhibits excellent energy conversion and storage properties. However, as its intrinsic metallic phase, little is known about the nature of 2D 1T'-MoS2 , probably because of limited phase uniformity (<80%) and lateral size (usually <1 µm) in produced materials. Herein, solution processing to realize high phase-purity 1T'-MoS2 monolayers with large lateral size is demonstrated. Direct chemical exfoliation of millimeter-sized 1T' crystal is introduced to successfully produce a high-yield of 1T'-MoS2 monolayers with over 97% phase purity and unprecedentedly large size up to tens of micrometers. Furthermore, the large-sized and high-quality 1T'-MoS2 nanosheets exhibit clear intrinsic superconductivity among all thicknesses down to monolayer, accompanied by a slow drop of transition temperature from 6.1 to 3.0 K. Prominently, unconventional superconducting behavior with upper critical field far beyond the Pauli limit is observed in the centrosymmetric 1T'-MoS2 structure. The results open up an ideal approach to explore the properties of 2D metastable polymorphic materials.