Acid-Assisted Soft Chemical Route for Preparing High-Quality Superconducting 2M-WS₂

Abstract

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 K x WS2; 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 K x WS2 is spontaneous, and a non-oxidative acidic reaction environment is sufficient to facilitate the oxidation of K x WS2 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.

Controllable superconducting to semiconducting phase transition in topological superconductor 2M-WS2

“…In the past decade, notable progress in structural phase transitions between 2H and 1T or 1T ′ phases in 2D MX 2 atomic layers has been achieved through different techniques, including temperature [36,37], strain [38][39][40], laser irradiation [41,42], and electrostatic doping [43][44][45], etc. However, phase transitions between topological superconducting and semiconducting phases (figure 1(a)) or other phases in 2D TMDs are still rare [46,47]. As a result, investigating structural phase transitions in 2D superconductors is crucial for deepening our understanding of their fundamental physical properties and unlocking potential applications in future quantum devices.…”