Unusual upper critical fields of the topological nodal-line semimetal candidate Sn _x NbSe_2−δ

Abstract

We report superconductivity in Sn x NbSe2−δ , a topological nodal-line semimetal candidate with a noncentrosymmetric crystal structure. The superconducting transition temperature T c of this compound is extremely sensitive to Sn concentration x and Se deficiency δ, 5.0 K for Sn0.13NbSe1.70 and 8.6 K for Sn0.14NbSe1.71 and Sn0.15NbSe1.69. In all samples, the temperature dependence of the upper critical field H c2(T) differs from the prediction of the Werthamer–Helfand–Hohenberg theory. While the zero-temperature value of the in-plane upper critical field of Sn x NbSe2−δ with the higher T c is lower than the BCS Pauli paramagnetic limit H P, that of the lower T c sample exceeds H P by a factor of ∼2. Our observations suggest that a possible odd-parity contribution dominates the superconducting gap function of Sn x NbSe2−δ , and it can be fine-tuned by the Sn concentration and Se deficiency.

Unusual superconductivity in the topological nodal-line semimetal candidate Sn x NbSe2-δ

“…Sn x NbSe 2−δ undergoes a superconducting transition at low temperatures [10]. Figure 1 shows the typical temperature dependence of resistivity of Sn x NbSe 2−δ .…”

“…Single crystals of Sn x NbSe 2−δ were grown by using a self-flux method [10]. The typical size of the resulting crystals is about 1 × 1 × 0.3 mm 3 .…”

High-Throughput Computational Screening and Design of CaPtAs-like Equiatomic Ternary Noncentrosymmetric Superconductors

“…In recent years, there has been a growing interest in noncentrosymmetric superconductors (NCSs), which can be defined as a type of superconductor that lacks an inversion center in the crystal structure. − One significant effect in NCSs is the antisymmetric spin–orbit coupling (ASOC), which allows for the mixed paring of spin-singlet and spin-triplet states under superconducting transition temperatures ( T c ), i.e., the (s + p)-wave paring. ,, These unconventional excitations make the existence of the Majorana zero modes or Majorana corner modes possible, which are treated as promising cornerstone that can be manipulated to realize the fault-tolerant topological quantum computations. − In addition, the presence of these mixed pairing can go beyond the conventional Bardeen–Cooper–Schrieffer (BCS) frame, displaying distinctive characteristics, which can lead to some fascinating properties such as nodal superconducting gaps , and anisotropic upper critical fields that surpass the Pauli limit …”

“…18−21 In addition, the presence of these mixed pairing can go beyond the conventional Bardeen−Cooper−Schrieffer (BCS) frame, 22 displaying distinctive characteristics, which can lead to some fascinating properties such as nodal superconducting gaps 8,23 and anisotropic upper critical fields that surpass the Pauli limit. 24 More intriguingly, some NCSs have captured wide attention due to their ability to explore an exotic physical phenomena, that is, the spontaneous time-reversal symmetry (TRS) breaking. 8,17,25,26 In general, there is no breaking of additional symmetries for conventional superconductors when entering the superconducting state, which can be accurately described by BCS theory.…”