First-principles prediction of superconducting properties of monolayer 1T'-WS2 under biaxial tensile strain.

High-purity 1T'-WS2 film has been experimentally synthesized [Nature Materials, 20, 1113-1120 (2021)] and theoretically predicted to be a two-dimensional (2D) superconducting material with Dirac cones [arXiv:2301.11425]. In the present work, we further study the superconducting properties of monolayer 1T'-WS2 by applying biaxial tensile strain. It is shown that the superconducting critical temperature Tc firstly increases and then decreases with respect to tensile strains, with the highest superconducting critical temperature Tc of 7.25 K under the biaxial tensile strain of 3%. In particular, we find that Dirac cones also exist in several tensile strained cases. Our studies show that monolayer 1T'-WS2 may provide a good platform for understanding the superconductivity of 2D Dirac materials.

Superconductivity of monolayer functionalized biphenylene with Dirac cones.

Monolayer biphenylene is a new two-dimensional (2D) carbon allotrope, which has been experimentally synthesized and theoretically predicted to show superconductivity. In this work, we investigate functionalized biphenylene with the adsorption of Li. The superconducting critical temperature (Tc) can be pushed from 0.59 K up to 3.91 K after Li adsorption. Our calculations confirm that the adsorption pushes the peak showing a high electronic density of states closer to the Fermi level, which usually leads to a larger Tc. Furthermore, the application of biaxial tensile strain can soften phonons and further enhance the Tc up to 15.86 K in Li-deposited biphenylene. Interestingly, a pair of type-II Dirac cones below the Fermi level has been observed, expanding the range of Dirac materials. It suggests that monolayer biphenylene deposited with Li may be a material with potential applications and improves the understanding of Dirac-type superconductors.

The effect of doping and strain on superconductivity of T-graphene.

As an allotrope of graphene, T-graphene was predicted to be an intrinsic two-dimensional (2D) superconductor with a superconducting critical temperature (Tc) of about 20.8 K [Gu et al., Chin. Phys. Lett. 36, 097401 (2019)]. In this work, based on first-principles calculations, hole doping and biaxial tensile strain (BTS) are considered to modulate the electron-phonon coupling (EPC) and superconductivity of T-graphene. It is found that the EPC constant of T-graphene is 0.807 and the calculated critical temperature Tc is 28.2 K at a doping level of 0.5 hole per unit cell (3.31 × 1014 cm-2) and 12% BTS. Furthermore, when 0.8 hole per unit cell (5.43 × 1014 cm-2) doping and 10% BTS are applied, the EPC constant is 0.939, and the Tc can be boosted to 35.2 K, which is higher than those of the pristine T-graphene and many other 2D carbon-based superconductors.