Superconductivity in the presence of disorder in skutterudite-related La3Co4Sn13 and La3Ru4Sn13 compounds: Electrical transport and magnetic studies

Abstract

a b s t r a c tLa 3 Co 4 Sn 13 and La 3 Ru 4 Sn 13 were categorized as BCS superconductors. In a plot of the critical field H c2 vs T, La 3 Ru 4 Sn 13 displays a second superconducting phase at the higher critical temperature T + c , characteristic of inhomogeneous superconductors, while La 3 Co 4 Sn 13 shows bulk superconductivity below T c . We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds. Additionally, for La 3 Ru 4 Sn 13 we find that dT + c =dP > dT c =dP. The pressure dependences of T c are interpreted according to the McMillan theory and understood to be a consequence of lattice stiffening. The investigation of the superconducting state of La 3 Co x Ru 4Àx Sn 13 shows a T + c that is larger then T c for x < 4. This unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.

Second-order structural transition in the superconductorLa3Co4Sn13

“…1). The superconducting phase transition temperature is consistent with previous reports [24,25]. When a magnetic field is applied, the superconductivity can be suppressed.…”

“…[23,24]. It is a superconductor with a T c of ∼2.7 K [24,25]. Incidentally, La 3 Co 4 Sn 13 has been shown to exhibit a feature at T * ∼ 152 K, which is detectable in the electrical resistivity, the heat capacity, the NMR Knight shift, and the nuclear spin-lattice relaxation rate [10,11].…”

The effective increase in atomic scale disorder by doping and superconductivity in Ca3Rh4Sn13

“…It is interesting to show whether the effect of disorder could also be observed in ρ (T) data under external pressure, where pressure is another control parameter. Our investigations do not confirm this hypothesis (see figures 3, also figure 8 in [13], and figures 9 and 10 in [19]), which means that inhomogeneity is the direct cause of the…”

“…Recently, we documented experimentally, that the effect of nanoscale disorder generated by doping of the Ca 3 Rh 4 Sn 13 [12] and isostructural La 3 M 4 Sn 13 [13] superconductors leads to the appearance of an inhomogeneous superconducting state, characterized by the critical temperature T c  higher than T c of the bulk phase. Similar interesting behavior has been observed in a number of other strongly-correlated superconductors (see, e.g., [13][14][15][16][17][18][19]), particularly those close to a quantum critical point (QCP), where an increase of T c was documented by nanoscale electronic disorder. In the critical regime, such a system is at the threshold of an instability, and even a weak perturbation, such as disorder can cause significant macroscopic effects.…”

γ-U phase in U-Pt system retained to low temperatures by means of rapid cooling

“…We notice here that a sequence of two transitions has been observed (by e.g. double anomalies in the temperature dependence of the susceptibility) in the skutterudite-related La 3 Rh 4 Sn 13 and La 3 Ru 4 Sn 13 [44,45] T/K) [47]. The difference is that the T c values of splat-cooled γ-U alloys are lower than 2.2 K,…”