Electronic Tuning and Uniform Superconductivity in ${\mathrm{CeCoIn}}_5$

We report a globally reversible effect of electronic tuning on the magnetic phase diagram in ${\mathrm{CeCoIn}}_5$ driven by electron (Pt and Sn) and hole (Cd, Hg) doping. Consequently, we are able to extract the superconducting pair breaking component for hole and electron dopants with pressure and codoping studies, respectively. We find that these nominally nonmagnetic dopants have a remarkably weak pair breaking effect for a $d$-wave superconductor. The pair breaking is weaker for hole dopants, which induce magnetic moments, than for electron dopants. Furthermore, both Pt and Sn doping have a similar effect on superconductivity despite being on different dopant sites, arguing against the notion that superconductivity lives predominantly in the ${\mathrm{CeIn}}_3$ planes of these materials. In addition, we shed qualitative understanding on the doping dependence with density functional theory calculations.

Figure 1

(a),(b): The temperature dependence of the electrical resistivity of ${\mathrm{CeCoIn}}_{5-x}{\mathrm{Sn}}_x$, ${\mathrm{CeCo}}_{1-x}{\mathrm{Pt}}_x{\mathrm{In}}_5$, ${\mathrm{CeCo}}_{0.91}{\mathrm{Pt}}_{0.09}{\mathrm{In}}_{5-y}{\mathrm{Hg}}_y$ and $\mathrm{CeCo}({\mathrm{In}}_{4.91}{\mathrm{Sn}}_{0.09}{)}_{1-(y/5)}{\mathrm{Hg}}_y$. Inset to (a) crystal structure of ${\mathrm{CeCoIn}}_5$ which can be viewed as an alternating series of active ${\mathrm{CeIn}}_3$ and buffer $T{\mathrm{In}}_2$ layers; and (b) low temperature resistivity of ${\mathrm{CeCoIn}}_5$ and the optimally tuned codoped samples. Also shown is ${\mathrm{CeCoIn}}_{4.95}{\mathrm{Cd}}_{0.05}$ at $P=1.6\mathrm{GPa}$.

Figure 2

(a) Temperature-composition phase diagram and (b) $T_c$ vs ${\rho }_0$ for ${\mathrm{CeCoIn}}_{5-x}{\mathrm{Sn}}_x$ and ${\mathrm{CeCo}}_{1-x}{\mathrm{Pt}}_x{\mathrm{In}}_5$. (c) $T^{*}$ vs $x$ and $y$ for ${\mathrm{CeCoIn}}_{5-x}{\mathrm{Sn}}_x$, ${\mathrm{CeCoIn}}_{5-y}{\mathrm{Cd}}_y$ ${\mathrm{CeCo}}_{1-x}{\mathrm{Pt}}_x{\mathrm{In}}_5$, ${\mathrm{CeCo}}_{0.91}{\mathrm{Pt}}_{0.09}{\mathrm{In}}_{5-y}{\mathrm{Hg}}_y$, and $\mathrm{CeCo}({\mathrm{In}}_{4.91}{\mathrm{Sn}}_{0.09}{)}_{1-(y/5)}{\mathrm{Hg}}_y$.

Figure 3

DFT results from three supercell calculations of Cd, Sn, and Hg doping in ${\mathrm{CeCoIn}}_5$. (a) Comparison of the PDOS of the Cd impurity to a well removed In(1) site. Also shown is the PDOS from an identical calculation with Hg (dotted line) overlapping with the Cd curve. (b) Same as (a) but for the calculation done with Sn doping. (c) and (d) PDOS of Ce1 atoms which neighbor the dopant atom, and Ce2 which are furthest from the Cd and Sn dopant atom, respectively.

Figure 4

(a) Pressure dependence of $T_c$ of ${\mathrm{CeCoIn}}_{5-y}{\mathrm{Cd}}_y$ samples. (b) Temperature-composition phase diagram of ${\mathrm{CeCo}}_{0.91}{\mathrm{Pt}}_{0.09}{\mathrm{In}}_{5-y}{\mathrm{Hg}}_y$ and $\mathrm{CeCo}({\mathrm{In}}_{4.91}{\mathrm{Sn}}_{0.09}{)}_{1-(y/5)}{\mathrm{Hg}}_y$. (c) $T_c$ suppression vs conservative estimates of the scattering rate for ${\mathrm{CeCoIn}}_{4.95}{\mathrm{Cd}}_{0.05}$, ${\mathrm{CeCoIn}}_{4.88}{\mathrm{Sn}}_{0.09}{\mathrm{Hg}}_{0.026}$ and ${\mathrm{CeCo}}_{0.91}{\mathrm{Pt}}_{0.09}{\mathrm{In}}_{4.97}{\mathrm{Hg}}_{0.026}$ (see text). The latter two have had the contribution to the scattering rate and $T_c$ suppression from Hg subtracted to isolate the effects due to the electron dopants (Sn and Pt). The solid black line is the expectation for a $d$-wave SC based on AG theory.