In the Yb-Co-Sn system a Remeika phase ${\mathrm{Yb}}_{3+x}{\mathrm{Co}}_4{\mathrm{Sn}}_{13-x}$ is found with solid solution extending within $0\le x\le 0.5$. All these compounds crystallize with primitive cubic (space group $Pm\overline{3}n, a\approx 9.54\AA$) strongly disordered ${\mathrm{Sc}}_3{\mathrm{Ir}}_4{\mathrm{Si}}_{13+x}$ type. Stoichiometric ${\mathrm{Yb}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$ is a superconductor with critical temperature $T_c=3.1\left(2\right)\mathrm{K}$, lower- $[B_{\mathrm{c}}1=1.90\left(2\right)\mathrm{mT}]$ and upper $[B_{\mathrm{c}}2=2.16\left(5\right)\mathrm{T}]$ critical fields. The specific-heat jump $\mathrm{\Delta }{c}_p/\gamma T_c=1.72\left(9\right)$ together with the fact that $B_{\mathrm{c}}2\left(T_c\right)$ 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 ${\mathrm{Yb}}_{3.2}{\mathrm{Co}}_4{\mathrm{Sn}}_{12.8}$ reveals $T_c=2.4\left(2\right)\mathrm{K}$ and $B_{\mathrm{c}}2=4.79\left(9\right)\mathrm{T}$ exceeding the classical Pauli limit. Strong electron-phonon coupling in this superconductor is confirmed by the high value of the ${\lambda }_{\mathrm{AD}}=0.92\left(2\right)$ parameter determined from the Allen-Dynes formula. However, the electronic specific heat of ${\mathrm{Yb}}_{3.2}{\mathrm{Co}}_4{\mathrm{Sn}}_{12.8}$ follows the exponential law $[c_{\mathrm{el}}\left(T\right)\propto e^{-\mathrm{\Delta }\left(0\right)/k_{\mathrm{B}}T}]$ and can be described by the $\alpha$-model $[\alpha \equiv \mathrm{\Delta }\left(0\right)/k_{\mathrm{B}}{T}_c=2]$ indicating this stannide to be a conventional BCS-superconductor. Both ${\mathrm{Yb}}_{3+x}{\mathrm{Co}}_4{\mathrm{Sn}}_{13-x}$ ($x=0,0.2$) 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.

Close

PrevNext

View figure in article

• Density of states
• Electronic structure
• Structural properties
• Superconducting gap
• Superconducting order parameter
• Superconducting phase transition
• Superconductors