Heavy Fermion Superconductivity and Magnetic Order in Noncentrosymmetric ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$

${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ is a novel heavy fermion superconductor, crystallizing in the ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{B}$ structure as a tetragonally distorted low symmetry variant of the ${\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{u}}_3$ structure type. ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ exhibits antiferromagnetic order at $T_N\approx 2.2\mathrm{K}$ and enters into a heavy fermion superconducting state at $T_c\approx 0.75\mathrm{K}$. Large values of $H_{c2}^{\prime }\approx -8.5\mathrm{T}/\mathrm{K}$ and $H_{c2}(0)\approx 5\mathrm{T}$ refer to heavy quasiparticles forming Cooper pairs. Hitherto, ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ is the first heavy fermion superconductor without a center of symmetry.

Figure 1

Crystal structure of ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$. The bonds indicate the pyramidal coordination $[{\mathrm{P}\mathrm{t}}_5]\mathrm{S}\mathrm{i}$ around the Si atom. Origin shifted by ($0.5,0.5,0.8532$) for convenient comparison with the parent ${\mathrm{A}\mathrm{u}\mathrm{C}\mathrm{u}}_3$ structure.

Figure 2

(a) Temperature dependent electrical resistivity $\rho$ of ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ and ${\mathrm{L}\mathrm{a}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ plotted on a logarithmic temperature scale. The magnetic contribution ${\rho }_{\mathrm{m}\mathrm{a}\mathrm{g}}(T)$ (dashed line) refers to the right axis. (b) Low temperature details of $\rho (T)$ of ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$. The solid line is a least squares fit (see text) and the dashed line shows $d\rho (T)/dT$.

Figure 3

Temperature dependent specific heat $C_p$ of ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ and ${\mathrm{L}\mathrm{a}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ plotted as $C_p/T$ vs $\ln T$. The solid and dashed lines are least squares fits (see text). Right axis: temperature dependent magnetic entropy $S_{\mathrm{m}\mathrm{a}\mathrm{g}}$ of ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ (dash-dotted line).

Figure 4

(a) Temperature dependent specific heat $C_p/T$ of ${\mathrm{C}\mathrm{e}\mathrm{P}\mathrm{t}}_3\mathrm{S}\mathrm{i}$ for various values of applied fields; vertical lines indicate the SC transition. (b) Temperature dependence of the upper critical field $H_{c2}$ deduced from specific heat and resistivity measurements. The solid straight line yields $H_{c2}^{\prime }\approx -8.5\mathrm{T}/\mathrm{K}$, and the dashed line is a guide to the eyes.