Superconductivity, magnetism, and atomic rattling phenomena in R ₃Rh₄Ge₁₃ (R =Y, Yb, Lu)

We give a first report of the physical properties of the pair of cubic intermetallic compounds R₃Rh₄Ge₁₃, with R being either Yb or Lu. The crystal structure can be described in terms of 3 atomic cages, and we reveal how certain thermal physical properties are inherent to this particular atomic layout. Close to room temperature, Yb₃Rh ₄Ge₁₃ displays strong paramagnetism originating from Yb³⁺ ions, but upon cooling though 100 K the magnetic susceptibility and electrical resistivity behave according to a thermally driven valence instability, and we classify Yb3Rh4Ge13 therefore as an intermediate valent f-electron system. Lu3Rh4Ge13 behaves in a diamagnetic manner throughout our accessible temperature range, - first with a weakly temperature-dependent magnetic susceptibility below room temperature, and finally with a precipitous drop in the electrical resistivity to zero at 2.5 K when superconductivity sets in.