Abstract Body

Superconductivity in WS₂ with the superconducting transition temperature T_c=8.8K which is the highest among all transition-metal dichalcogenides has recently been discovered [1] and has attracted considerable attention as a candidate material for topological superconductivity [2,3]. When pressure is applied, T_c decreases monotonically with increasing pressure down to 3.5K at 18GPa above which a broad transition region from the 2M structure to the 3R structure is observed up to 40GPa where the system shows a semiconducting behavior with no superconductivity [4]. At further higher pressures above 45GPa, 3R-WS₂ becomes metallic and shows superconductivity with T_c of 2.5 K almost independent of pressure up to 65GPa [4]. In our previous work [5], we have investigated the pressure dependence of T_c of WS₂ based on the first-principles calculation and have found that, in 2M-WS₂, the obtained T_c decreases with increasing pressure as observed in the experiments although the values of T_c are about 1/3~1/6 of the experimental values. As for 3R-WS₂, T_c is estimated to be zero independent of pressure and then the conventional BCS phonon mechanism is considered to fail to account for the superconductivity in 3R-WS₂.

In the present paper, we then focus especially on 3R-WS₂ to discuss a possible unconventional mechanism of the superconductivity. Figure 1 (a) shows the first-principles results of the Fermi surfaces (FSs) of 3R-WS₂, where there are three small hole FSs centered at the G point (A, B, and C) and six small electron FSs between the G point  and the six K points (D). Based on the band dispersions obtained from the first-principles calculations, the bare susceptibilities in the band representation are calculated and plotted in Figure 1 (b), where the intra-band component of the electron band (D-D) shows a peak at the M point due to the nesting between the six electron FSs in addition to a peak at the G point, while the inter-band components between the hole and electron FSs (A-D, B-D and C-D) show peaks at the incommensurate wave vectors due to the nesting between the three hole FSs and the six electron FSs. Those peaks of the susceptibilities are considered to represent the effects of CDW and/or excitonic fluctuations as have been discussed in many layered transition-metal dichalcogenides [6]. Then, we discuss a possible mechanism of the superconductivity due to the CDW and/or the excitonic fluctuations. Detailed results will be presented on the day of the conference.

References

[1] Y. Fang et al., Adv. Mater. 31, 1901942 (2019)
[2] Y. Yuan et al., Nature Physics 15, 1046 (2019)
[3] Y. W. Li et al., Nature Communications 12, 2874 (2021)
[4] W. Zhang et al., J. Phys. Chem. Lett. 12, 3321 (2021)
[5] Y. Wang, T. Sekikawa, K. Sano and Y. Ōno, The 24th Asian Workshop on First-Principles Electronic Structure Calculations, Oct. 30-Nov. 1, 2023, Fudan University, Shanghai, China
[6] S Manzeli et al., Nat. Rev. Mater. 2, 17033 (2017).

Acknowledgment

This work was partially supported by JSPS KAKENHI Grant Number 21K03399 and the Niigata University Fellowship System. Numerical calculations were performed in part using the facilities of the Center for Computational Sciences, University of Tsukuba and Center for Computational Materials Science, Institute for Materials Research, Tohoku University.