SmPt$_4$Ge$_{12}$ -- a filled skutterudite with exotic heavy-fermion properties

Ternary samarium-filled platinum-germanium skutterudite SmPt$_4$Ge$_{12}$ was prepared at a pressure of 5.0(0.5)\,GPa and a temperature of 1070(70)\,K. The compound crystallizes in the cubic space group $Im\bar{3}$ ($a$ = 8.6069(4)\,\AA) and is isotypic with LaFe$_4$P$_{12}$. X-ray absorption spectroscopy measurements show that samarium in SmPt$_4$Ge$_{12}$ has a temperature-independent intermediate valence ($\nu = 2.90 \pm 0.03$). Magnetization data reveal van-Vleck paramagnetism above $\sim$50\,K. The low-temperature specific heat displays a broad anomaly centred at 2.9\,K and a large linear coefficient $\gamma'$ = 450 mJ\,mol$^{-1}$K$^{-2}$ suggesting heavy-fermion behaviour. This state is remarkabkly field-independent and resembles the physics of SmOs$_4$Sb$_{12}$. [1] R Gumeniuk et al. New J. Physics 12 (2010) 103035.