Intermediate valence to heavy fermion through a quantum phase transition in Yb$_3$(Rh$_{1-x}T_x$)$_4$Ge$_{13}$ (${T}$ = Co, Ir) single crystals

Single crystals of Yb${_3}$(Rh$_{1-x}$$T$$_x$)${_4}$Ge$_{13}$ ($T$ = Co, Ir) have been grown using the self-flux method. Powder X-ray diffraction data on these compounds are consistent with the cubic structure with space group $Pm\bar{3}n$. Intermediate valence behavior is observed in Yb${_3}$(Rh$_{1-x}$$T$$_x$)${_4}$Ge$_{13}$ upon $T$ = Co doping, while $T$ = Ir doping drives the system into a heavy fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb${_3}$(Rh$_{1-x}$$T$$_x$)${_4}$Ge$_{13}$ for 0.5 $<$ $x$ $\leq$ 1 with T$_N$ = 0.96 K for Yb${_3}$Ir${_4}$Ge$_{13}$. With decreasing $x$, the magnetic order is suppressed towards a quantum critical point around $x_c$ = 0.5, accompanied by non-Fermi liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi liquid behavior is recovered with the application of large magnetic fields.