posted on 2023-07-13, 22:03authored byXiaoyu Song, Brianna Hoff, Ratnadwip Singha, Joseph W. Stiles, Grigorii Skorupskii, Jason F. Khoury, Guangming Cheng, Franziska Kamm, Ayelet J. Uzan, Stephanie Dulovic, Sanfeng Wu, Florian Pielnhofer, Nan Yao, Leslie M. Schoop
2M-WS2 is a metastable, superconducting polymorph
of
the transition metal dichalcogenide (TMD) WS2, comprised
of layers of face-sharing distorted WS6 octahedra. It is
predicted to host non-Abelian quantum states, promising for topological
computing. Due to its thermodynamic instability, 2M-WS2 cannot be synthesized using solid-state synthesis. Rather, it requires
a top-down approach in which K+ is deintercalated from
KxWS2; so far, this process
has been completed using a strong oxidizer, K2Cr2O7 in dilute H2SO4. A disadvantage
of such an indirect synthesis is that the harsh reaction condition
may cause the crystal quality to suffer. To date, no studies have
been performed to optimize the synthesis or understand the chemical
nature of this reaction. In this study, we found that the K-deintercalation
process from KxWS2 is spontaneous,
and a non-oxidative acidic reaction environment is sufficient to facilitate
the oxidation of KxWS2 to 2M-WS2 while reducing H+ to H2. By analyzing
the superconducting transition in the heat capacity, we found that
2M-WS2 made using less aggressive methods has higher superconducting
volume fractions. We describe how to access the thermodynamically
unfavorable superconducting 2M phase of WS2 as high-quality
crystals.