Abstract:The zero-field critical temperature and the coherence length in the layered superconductor 2H-NbSe2-xSx (x=O-2.0) were investigated. The zero-field critical temperature decreases with increasing the residual resistivity. This result can be explained in terms of the three-dimensional Anderson localization with the mobility edge below the Fermi level The coherence length as a function of x can be explained by the theory of the anisotropic three-dimensional dirty superconductor. However it shows anomalous behavio… Show more
When sulfur and silicon are incorporated in monolayer 2H-NbSe2 the superconducting transition temperature, Tc, has been found to vary non-monotonically. This was assumed to be a manifestation of fractal superconductivity. Using first-principles calculations, we show that the nonmonotonic dependence of Tc is insufficient evidence for multifractality. A unifying aspect in our study are selenium vacancies in NbSe2, which are magnetic pair-breaking defects that we propose can be present in considerable concentrations in as-grown NbSe2. We show that sulfur and silicon can occupy the selenium sites and reduce the pair-breaking effect. Furthermore, when sulfur is incorporated in NbSe2, the density of states at the Fermi level and the proximity to magnetism in the alloy are both reduced compared to the parent compound. Based on our results, we propose an alternative explanation of the non-monotonic change in Tc which does not require the conjecture of multifractality.
When sulfur and silicon are incorporated in monolayer 2H-NbSe2 the superconducting transition temperature, Tc, has been found to vary non-monotonically. This was assumed to be a manifestation of fractal superconductivity. Using first-principles calculations, we show that the nonmonotonic dependence of Tc is insufficient evidence for multifractality. A unifying aspect in our study are selenium vacancies in NbSe2, which are magnetic pair-breaking defects that we propose can be present in considerable concentrations in as-grown NbSe2. We show that sulfur and silicon can occupy the selenium sites and reduce the pair-breaking effect. Furthermore, when sulfur is incorporated in NbSe2, the density of states at the Fermi level and the proximity to magnetism in the alloy are both reduced compared to the parent compound. Based on our results, we propose an alternative explanation of the non-monotonic change in Tc which does not require the conjecture of multifractality.
“…However, superconductivity and CDW are weakly linked in NbSe2. In the bulk form, both of them are simultaneously suppressed by substituting Se with S atoms 50 . As a matter of fact, only 1% of the total density of states at the Fermi surface of bulk NbSe2 is involved in the formation of CDW [51][52][53] .…”
The interplay between disorder and superconductivity is a subtle and fascinating phenomenon in quantum many body physics. The conventional superconductors are insensitive to dilute nonmagnetic impurities, known as the Anderson's theorem 1 .Destruction of superconductivity and even superconductor-insulator transitions 2-10 occur in the regime of strong disorder. Hence disorder-enhanced superconductivity is rare and has only been observed in some alloys or granular states 11-17 . Because of the entanglement of various effects, the mechanism of enhancement is still under debate.Here we report well-controlled disorder effect in the recently discovered monolayer
“…We summarize the relationship of T c and carrier concentration (50 K) of the three samples in the inset of figure 4(b). In 2Ha-NbSe 2 , most doping and intercalation will decrease its T c [34][35][36][37][38], and only pressure can increase its T c a little [39]. We speculate that the undoped 2Ha-NbSe 2 is very close to optimally doping point.…”
We report the discovery of superconductivity with T c of about 5.3 K in a new misfit layered compound (SnSe) 1.16 (NbSe 2 ) 2 . High resolution transmission electron microscopy and selected area electron diffraction of the single-crystalline samples clearly reveal the misfit layered structure. Based on the McMillan equation, the electron-phonon coupling constant λ e-ph is estimated to be about 0.96, which is close to strong coupling range. The estimated out-of-plane and in-plane upper critical magnetic fields are 8.9 T and 15.5 T respectively. H ab c2 (0) is 1.74 times the value of Pauli paramagnetic limit. Moreover, there is a positive curvature in the ( ) H T c2 curves near T c , indicating a feature of multi-band superconductivity. The temperature dependence of specific-heat in superconducting state can be fit by a two-band BCS model, which confirms further the multi-band superconductivity. The reduced charge transfer between the two subsystems may account for the enhanced T c comparing with (SnSe) 1.16 (NbSe 2 ).
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