Non-Fermi-liquid behavior at the antiferromagnetic quantum critical point in the heavy-fermion system Ce(Cu1−xCox)2Ge2

Polycrystalline samples of $\mathrm{Ce}{({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Co}}_x)}₂{\mathrm{Ge}}₂$ were investigated by means of electrical resistivity $\ensuremath{\rho}(T)$, magnetic susceptibility $\ensuremath{\chi}(T)$, specific heat ${C}_p(T)$, and thermoelectric power $S(T)$ measurements. The long-range antiferromagnetic order, which set in at ${T}_N=4.1\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ in ${\mathrm{CeCu}}₂{\mathrm{Ge}}₂$, is suppressed by non-isoelectronic cobalt doping at a critical value of the concentration ${x}_c=0.6$, accompanied by non-Fermi-liquid behavior inferred from the power-law dependence of heat capacity and susceptibility, i.e., $C(T)/T$ and $\ensuremath{\chi}(T)\ensuremath{\propto}{T}^{\ensuremath{-}1+\ensuremath{\lambda}}$, down to 0.4 K, along with a clear deviation from ${T}²$ behavior of the electrical resistivity. However, we have not seen any superconducting phase in the quantum critical regime down to 0.4 K.