Anisotropic flux creep and vortex pinning in the misfit-layered superconductor (SnS) 1.15 TaS 2

Abstract

Misfit-layered compounds provide bulk crystalline platforms for accessing quasi-two-dimensional superconductivity because electronically active transition-metal dichalcogenide layers are separated by incommensurate spacer layers. Here we investigate field-orientation-dependent vortex dynamics and flux pinning in single-crystalline (SnS) 1.15 TaS 2 , a natural superlattice composed of TaS 2 layers and SnS spacer layers. Electrical transport shows a strongly anisotropic upper critical field, with H ab c2 (0) exceeding the weak-coupling Pauli limit. In addition, AC susceptibility at zero DC field reveals a pronounced frequency-dependent shift of the dissipative χ ′′ peak for H AC ∥ c, whereas the shift is much weaker for H AC ∥ ab, indicating an anisotropic thermally activated flux response under ac excitation. TAFF analysis further shows that the activation energy is substantially larger for H ∥ ab than for H ∥ c and that, for H ∥ c, the pinning potential crosses over from a weak low-field dependence to a steeper high-field dependence. These results identify (SnS) 1.15 TaS 2 as a useful bulk misfit-layered platform for studying orientation-dependent vortex dissipation and pinning in quasi-two-dimensional superconductors.