Unconventional superconducting phase in NbSe₂-based misfit layered superconductor

Two-dimensional (2D) superconductor is a good playground for investigating quantum transport. Recently, bulk 2D superconductors, where superconducting layers are well separated by non-superconducting block layers, has been intensively studied [1,2]. Among them, misfit layered compound, which consist of alternately stacked layers with incompatible unit cells [3], is a unique material, offering a new opportunity for exploring low dimensional superconductivity.

In this work, we report transport properties of misfit layered superconductor composed of NbSe₂. In this material, trilayer NbSe₂ layers are separated by PbSe block layers. Firstly, we found that the superconducting transition temperature is close to the exfoliated trilayer NbSe₂. Secondly, we observed an anomaly in temperature dependence of in-plane upper critical field, which suggests the unconventional superconductivity in low-temperature and high-magnetic-field region. Since this anomaly is absent in bulk and exfoliated trilayer NbSe₂ [4,5], we assume that PbSe block layers play crucial role in the emergence of unconventional superconducting phase in the present system.

[1] A. Devarakonda et al., Science 370, 231 (2020).

[2] P. Samuely et al., PRB 104, 224507 (2021).

[3] N. Ng and T. M. McQueen, APL Mater. 10, 100901 (2022).

[4] X. Xi et al., Nat. Phys. 12, 139 (2016).

[5] E. Sohn et al., Nat. Commun. 17, 504 (2018).