Intermediate Valence to Heavy Fermion Through a Quantum Phase Transition in Yb₃(Rh₁₋xTx)₄ Ge₁₃ (T = Co, Ir) Single Crystals

Single crystals of Yb₃(Rh₁₋xTx)₄ Ge₁₃ (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 Pm3̅n. Intermediate-valence behavior is observed in Yb₃(Rh₁₋xTx)₄ Ge₁₃ 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 Yb₃(Rh₁₋xTx)₄ Ge₁₃ for 0.5 < x ≤ 1 with T_N = 0.96 K for Yb₃Ir₄Ge₁₃. 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.