Fig. 1: Observation of a tunable superconducting state in atomically thin 1T’-WS2.
a Crystal structure and the unit cell of 1 T’-WS2 crystal. b Optical microscopy image of an atomically thin 1T’-WS2 flake, obtained through mechanically exfoliation from the crystal’s bc plane and subsequently encapsulated with hBN. The flake, comprising approximately twelve atomic layers, is demarcated by white dashed lines. Current (I+ and I−) and voltage (V+ and V−) probes for four-terminal electrical transport measurements are also marked. c Atomic force microscopy (AFM) image of a 1 T’-WS2 flake with the same optical contrast as the flake in (b). d AFM height (h) profile collected along the green line in (c) (the arrow indicates the directions of the scan), revealing a thickness of \(h\simeq 6.4\) nm that aligns with the expected thickness for twelve atomic layers of 1T’-WS2. e Critical temperature (Tc) of the superconducting transition plotted against the external hydrostatic pressure (P). Initially, Tc decreases with increasing pressure, leading to the disappearance of the superconducting state SC1 (pink-shaded region), at \(P=1.15\) GPa. However, at \(P=1.8\) GPa, a new superconducting state (SC2; purple shaded region) emerges with a smaller Tc relative to SC1. f Out-of-plane upper critical magnetic field (\({\mu }_{0}{H}_{c2\perp {bc}}\)) plotted against pressure. Akin to Tc, \({\mu }_{0}{H}_{c2\perp {bc}}\) decreases with increasing P in the SC1 state and then resuscitates with a smaller value in the SC2 state. The inset shows the P dependence of \({\mu }_{0}{H}_{c2\perp {bc}}\) normalized by Tc, with \({\mu }_{0}{H}_{c2\perp {bc}}/{T}_{c}\) being smaller in the SC2 state. g Pressure-dependence of the in-plane upper critical magnetic field (\({\mu }_{0}{H}_{c2{||bc}}\)). Like Tc and \({\mu }_{0}{H}_{c2\perp {bc}}\), \({\mu }_{0}{H}_{c2{||bc}}\) decreases with increasing P in the SC1 state. However, \({\mu }_{0}{H}_{c2{||bc}}\) in the SC2 state becomes similar in magnitude to that of the SC1 state, despite the comparatively much smaller Tc and \({\mu }_{0}{H}_{c2\perp {bc}}\). The inset illustrates the P dependence of \({\mu }_{0}{H}_{c2{||bc}}\) normalized by Tc, revealing a nearly two-fold larger \({\mu }_{0}{H}_{c2{||bc}}/{T}_{c}\) in the SC2 state. Data in (e-g) were obtained from three samples with identical thicknesses, and are represented by the purple, green, and orange data points. Source data are provided as a Source Data file.
