Superconductivity and phase transition in quasi-one-dimensional sulfide AV6S8 (A=In, T1, K, Rb, Cs)

Superconductivity and charge density wave formation in TlxV6S8

“…This is corroborated by electronic band structure calculations which indicate nesting conditions for at least four characteristic wave vectors [14]. Preliminary electron diffraction measurements reveal the existence of satellite spots at T < T CDW in addition to the main diffraction spots observed at low-T [11], similar to what was found for the CDW-compounds Nb 3 Te 4 [15] and InNb 3 Te 4 [16]. Moreover, the formation of a CDW state was suggested also for the iso-structural compounds AV 6 S 8 with A = In, K, Rb and Cs and also for V 6 S 8 .…”

“…Despite the partial gapping at T < T CDW , Tl x V 6 S 8 adopts a SC ground state at much lower temperatures. The superconductivity at T c ≈ 3.5 K was initially observed in resistivity measurements on single crystals of Tl 0.1 V 6 S 8 and Tl 0.8 V 6 S 8 by Bensch et al [17] and has been confirmed more recently by susceptibility studies on poly-crystalline samples [11,18]. Similar to the high temperature anomaly, superconductivity is found to be a common feature among the members of the AV 6 S 8 family as it is observed for intercalated Tl, In, K, Rb or Cs and also for the parent compound V 6 S 8 .…”

“…An ubiquitous enhancement of ρ(T ) upon lowering the temperature in these compounds suggests a reduction in the carrier density. A clear hysteresis of about T ≈ 40 K is found only for the In compound [11].…”

“…A slight upturn of ρ(T ) at T = T CDW with 150 K < T CDW < 170 K [11] and a simultaneous drop in the ac magnetic susceptibility χ(T ) [12] indicate a loss in DOS. This, coupled to a first-order structural phase transition revealed by x-ray measurements [13] and a sharp anomaly accompanied by latent heat in differential-scanning calorimetry (DSC) [11,12] in the same temperature range, indicate the possible formation of a CDW instability in this compound. This is corroborated by electronic band structure calculations which indicate nesting conditions for at least four characteristic wave vectors [14].…”

Interplay between superconductivity and charge density wave instability in Tl V6S8

“…An increase in rðTÞ and a drop in magnetic AC susceptibility wðTÞ at T h indicate a loss in the density of states (DOS) which is interpreted as charge density wave formation [3]. This hypothesis is supported by electronic band structure calculations which confirm nesting conditions for at least four characteristic wave vectors q [4].…”