Reversible Tuning of the Heavy-Fermion Ground State in ${\mathrm{CeCoIn}}_5$

Cadmium doping the heavy-fermion superconductor ${\mathrm{CeCoIn}}_5$ at the percent level acts as an electronic tuning agent, sensitively shifting the balance between superconductivity and antiferromagnetism and opening new ambient-pressure phase space in the study of heavy-fermion ground states.

Figure 1

Electronic specific heat ($C_{\mathrm{el}}=C-C_{\mathrm{latt}}$) divided by temperature for $\mathrm{CeM}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$ as a function of temperature. The lattice specific heat ($C_{\mathrm{latt}}$) is not shown. Values of $x$ represent the nominal Cd content of crystals, as explained in the text. (a) $\mathrm{CeCo}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$, (b) $\mathrm{CeRh}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$, (c) $\mathrm{CeIr}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$. The solid curve through the data for $x=0.0375$ in (c) is a fit to the form $C_{\mathrm{el}}/T=A\ln T/T_0$, where $A=240\mathrm{mJ}/\mathrm{mol}{\mathrm{K}}^2$ and $T_0=18\mathrm{K}$, for $0.4\mathrm{T}<4\mathrm{K}$. Insets in each panel are plots of magnetic entropy $S_{\mathrm{mag}}$ obtained from the area under associated $C_{\mathrm{el}}/T$ vs $T$ curves.

Figure 2

Dependence of superconducting transition temperatures $T_c$ and Néel temperatures $T_N$ on $x$, where $x$ is the nominal Cd content of crystals. See text for details. (a) $\mathrm{CeCo}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$, (b) $\mathrm{CeRh}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$, and (c) $\mathrm{CeIr}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$. For (b), $T_N{}^A$ and $T_N{}^B$ are associated with different antiferromagnetic (AFM) phases as discussed in the text. $T_c$ and $T_N$ were extracted from specific heat (Fig. 1) and confirmed with magnetic susceptibility measurements.

Figure 3

Results of pressure studies on $\mathrm{CeCo}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$. (a) Pressure dependence of the Néel $T_N$ and superconducting transition temperature $T_c$ for ${\mathrm{CeRhIn}}_5$ (black circles) [19] and $\mathrm{CeCo}({\mathrm{In}}_{1-x}{\mathrm{Cd}}_x{)}_5$ at nominal $x=0.10$ (blue squares) and 0.15 (red triangles). With ${\mathrm{CeRhIn}}_5$ as the reference, a rigid shift of nominal $x=0.15$ data by $+0.9\mathrm{GPa}$ and of nominal $x=0.10$ data by an additional $+0.7\mathrm{GPa}$ (i.e., a total shift of 1.6 GPa relative to ${\mathrm{CeRhIn}}_5$) superimposes all three sets of data. (b) Low temperature in-plane resistivity (${\rho }_{ab}$) at atmospheric and 0.45 GPa pressures for nominal $x=0.10$. Bulk superconductivity is confirmed by simultaneous ac susceptibility measurement. (c) In-plane resistivity (${\rho }_{ab}$) at atmospheric and 0.95 GPa pressures for nominal $x=0.15$. Bulk superconductivity is confirmed by simultaneous ac susceptibility measurement.