Multiple superconducting transitions in Yb3+xCo4Sn13−x

Abstract

In the Yb-Co-Sn system a Remeika phase Yb3+xCo4Sn13−x is found with solid solution extending within 0≤x≤0.5. All these compounds crystallize with primitive cubic (space group Pm3¯n, a≈9.54Å) strongly disordered Sc3Ir4Si13+x type. Stoichiometric Yb3Co4Sn13 is a superconductor with critical temperature Tc=3.1(2)K, lower- [Bc1=1.90(2)mT] and upper [Bc2=2.16(5)T] critical fields. The specific-heat jump Δcp/γTc=1.72(9) together with the fact that Bc2(Tc) dependence is described by the Werthamer-Helfand-Hohenberg (WHH) model hint toward a conventional mechanism with a weak electron-phonon coupling. Although a more precise analysis is hampered by the presence of multiple superconducting transitions observed in the specific heat of this Remeika phase, the nonstoichiometric Yb3.2Co4Sn12.8 reveals Tc=2.4(2)K and Bc2=4.79(9)T exceeding the classical Pauli limit. Strong electron-phonon coupling in this superconductor is confirmed by the high value of the λAD=0.92(2) parameter determined from the Allen-Dynes formula. However, the electronic specific heat of Yb3.2Co4Sn12.8 follows the exponential law [cel(T)∝e−Δ(0)/kBT] and can be described by the α-model [α≡Δ(0)/kBTc=2] indicating this stannide to be a conventional BCS-superconductor. Both Yb3+xCo4Sn13−x (x=0,0.2) compounds reveal complex phonon spectra with possible “rattling” behavior. They are also found to be metallic systems, some aspects of which can be described by a free-electron-gas model.

Source-reported materials — not catalogue approval

Similar papers