Experimental and first-principles studies of superconductivity in topological nodal line semimetal SnTaS₂

Abstract

We report a detailed study of superconductivity in polycrystalline SnTaS2 using electrical transport, magnetization and heat capacity measurements. SnTaS2 crystallizes in centrosymmetric hexagonal structure with space group P63/mmc. Electrical resistivity, magnetization and specific heat data suggest SnTaS2 to be a weakly coupled, type-II superconductor with Tc ≈ 2.8 K. First-principles calculations show signature for nodal line topology in the electronic band structure, protected by the spatial-inversion and time-reversal symmetries, that strongly gapped out by the inclusion of spin-orbit coupling (SOC). Superconductivity in layered SnTaS2 with nodal line topological state makes it a strong candidate to be considered for a 3D topological superconductor.

Superconductivity and weak anti-localization in nodal-line semimetal SnTaS2

“…The obtained XRD data were refined using Fullprof software to deduce the lattice parameters that come out to be a = b = 3.336 Å, c = 17.447 Å. This is in agreement with reported data [23,25,26]. The schematic unit cell of SnTaS 2 is shown in (inset (i) of figure 1(a)).…”

“…In such cases H c2,ab can be fitted using the equation H c2,ab (T) = H c2,ab (0) (1 − t 5/2 ) 5/2 [25]. The upward curvature in upper critical field (near T c ) seen here has been previously reported in SnTaS 2 [23,25,26], PbTaSe 2 [29,30] and other intercalated chalcogenides [9,31]. There are several possible origin for this upward curvature in upper critical field in H//ab direction.…”

“…The transition is quite sharp and its transition width is (∆T c = Tc onset − Tc zero = 0.24 K). The RRR (residual resistivity ratio = ρ(300 K)/ρ(4 K)) is estimated to be 530, which is the highest RRR reported in this system [23,25,26]. It reflects high quality of the single crystal that is devoid of defects and impurities.…”

“…Next, we turn to the question as to whether the superconducting state in SnTaS 2 is derived from non-trivial topological states as indicated in the reported electronic band structure [24,26]. As we know, WAL and nodal lines are normal state properties.…”

“…First principle calculations have shown that SnTaS 2 exhibits nodal-line band structure and drumhead like states when spin-orbit coupling (SOC) is excluded [23,24]. There have been some studies [23,25,26] on superconducting properties of SnTaS 2 but topological aspect related to non-trivial band structure is an open question. In specific, the experimental manifestations of non-trivial band structure in the normal and superconducting states are yet to be unambigously ascertained.…”