Abstract
${\mathrm{TaSnS}}_{2}$ single crystal and polycrystalline samples are investigated in detail by magnetization, electrical resistivity, and specific heat as well as Raman spectroscopy and nuclear magnetic resonance (NMR). Studies are focused on the temperature and magnetic field dependence of the superconducting state. We determine the critical fields for both directions $B\ensuremath{\parallel}c$ and $B\ensuremath{\perp}\phantom{\rule{0.16em}{0ex}}c$. Additionally, we investigate the dependence of the resistivity, the critical temperature, and the structure through Raman spectroscopy under high pressure up to 10 GPa. At a pressure of $\ensuremath{\approx}3\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ the superconductivity is suppressed below our minimum temperature. The Sn NMR powder spectrum shows a single line which is expected for the ${\mathrm{TaSnS}}_{2}$ phase and confirms the high sample quality. Pronounced de Haas-van Alphen oscillations in the ac susceptibility of polycrystalline sample reveal two pairs of frequencies indicating coexisting small and large Fermi surfaces. The effective mass of the smaller Fermi surface is $\ensuremath{\approx}0.5{m}_{\mathrm{e}}$. We compare these results with the band structures from DFT calculations. Our findings on ${\mathrm{TaSnS}}_{2}$ are discussed in terms of a quasi-two-dimensional BCS superconductivity.
Highlights
Superconductors with layered crystal structures have attracted the interest of researchers since the earlier 1960’s
TaSnS2 single crystal and polycrystalline samples are investigated in detail by magnetization, electrical resistivity, and specific heat as well as Raman spectroscopy and nuclear magnetic resonance (NMR)
The atomic coordinates obtained from direct methods (Table I) were consistent with those reported for TaSnS2 in Ref. [35]
Summary
Superconductors with layered crystal structures have attracted the interest of researchers since the earlier 1960’s This is mainly due to their anisotropic superconducting properties and the associated very high critical fields [1,2,3,4]. The layered crystal structure is characteristic for transition-metal dichalcogenides (TMD) Their properties are frequently said to be reminiscent of those of high-Tc cuprates and iron-based pnictides [4,17]. Powder neutron and x-ray diffraction [34] as well as single crystal x-ray diffraction [35] confirmed the presence of only one crystallographic Sn site in TaSnS2 These studies revealed a rather long Sn − S distance of about 2.8 Å, which again could be explained by the low charge of Sn. Superconductivity in TaSnS2 was reported recently [47]. Resistivity measurements and Raman studies under high pressure reveal the suppression of superconductivity with pressure and suggest a pressure-induced structural phase transition
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