F. Chen(A), T. Nagashima (A), K. Ishihara (A), K. Imamura (A), Romain
Grasset (B), Marcin Koczykowski (B), Y. Fujiwara (C), K. Kobayashi
(C,D), K. Hashimoto (A) and T. Shibauchi (A)

A: Department of Advanced Materials Science, University of Tokyo
B: École Polytechnique
C: Department of Science, Okayama University
D: RIES, Hokkaido University

The misfit-layered superconductor (PbS)_1.14(TaS₂)_n consists of alternating layers of insulating PbS and superconducting 1H-TaS₂. As shown in Fig 1, 1H-TaS₂ crystallizes in a non-centrosymmetric hexagonal structure, while 2H-TaS₂ consists of stacked 1H layers (H and H’) in an inversion-symmetric configuration. For n = 1, the structure contains monolayers of 1H-TaS₂ separated by PbS layers. For n = 2, two TaS₂ layers are stacked to form an inversion-symmetric 2H-TaS₂ bilayer within each PbS layer. This architecture serves as a platform to investigate how the TaS₂ layer number and inversion symmetry breaking affect superconductivity. Prior studies for n = 1 discuss possible Ising superconductivity in bulk but the pairing nature remains unresolved [1]. Investigating the superconducting gap structure in this material is essential to understanding the interplay between dimensionality, symmetry breaking, and electron correlations, providing new insights into unconventional superconducting mechanisms beyond BCS theory.

In this study, we examined the angular dependence of the upper critical field to probe the evolution of dimensionality with TaS₂ layer number. By performing penetration depth measurements on (PbS)_1.14(TaS₂)_n, we further determined that the low-energy excitations exhibit a nodeless superconducting gap structure. In this presentation, I will discuss our results in detail.

Fig 1. Crystal structure of (a) 1H-TaS₂, (b) 2H-TaS₂, (c) (PbS)_1.14TaS₂ and (d) (PbS)_1.14(TaS₂)₂ [1,2].

References: [1] S. K. P. Sajilesh et al., Phys. Rev. B 111, 054509 (2025). [2] L. Crippa et al., Nat. Commun. 15, 1357 (2024).