Heat transport study of field-tuned quantum criticality in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>CeIrIn</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>

The in-plane electrical resistivity, $\ensuremath{\rho}$, and thermal conductivity, $\ensuremath{\kappa}$, of the heavy-fermion superconductor ${\mathrm{CeIrIn}}_{5}$ were measured down to 40 mK in magnetic fields up to 11 T applied along the $c$ axis. For all fields above ${H}_{c2}=4$ T of filamentary superconductivity, we find that the ratio of heat and charge conductivities in the $T\ensuremath{\rightarrow}0$ limit obeys the Wiedemann-Franz law, $\ensuremath{\kappa}/T={L}_{0}/\ensuremath{\rho}$, where ${L}_{0}=2.45\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8} \text{W}\phantom{\rule{0.16em}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}{\text{K}}^{\ensuremath{-}2}$ is the Sommerfeld value of the Lorenz number. The temperature-dependent parts of both the electrical and thermal resistivity, $w\ensuremath{\equiv}T/{L}_{0}\ensuremath{\kappa}$, follow the functional dependence expected for the Fermi liquid theory of metals with $\ensuremath{\rho}\ensuremath{-}{\ensuremath{\rho}}_{0}=A{T}^{2}, w\ensuremath{-}{w}_{0}=B{T}^{2}$, with ${\ensuremath{\rho}}_{0}={w}_{0}$ and $B\ensuremath{\approx}2A$. The coefficient $B$ does not show a significant field dependence even upon approaching ${H}_{c2}=0.4$ T of the bulk superconducting state. The weak response to the magnetic field is in stark contrast with the behavior found in the closely related ${\mathrm{CeCoIn}}_{5}$, in which the field-tuned quantum critical point coincides with ${H}_{c2}$. The value of the electron-electron mass enhancement, as judged by the $A$ and $B$ coefficients, is about one order of magnitude reduced in ${\mathrm{CeIrIn}}_{5}$ as compared to ${\mathrm{CeCoIn}}_{5}$ (in spite of the fact that the zero field ${\ensuremath{\gamma}}_{0}$ in ${\mathrm{CeIrIn}}_{5}$ is twice as large as ${\ensuremath{\gamma}}_{0}$ in ${\mathrm{CeCoIn}}_{5}$), which suggests that the material is significantly farther away from the magnetic quantum critical point at bulk ${H}_{c2}$ and at all of the studied fields. A suppressed Kadowaki-Woods ratio in ${\mathrm{CeIrIn}}_{5}$ compared to ${\mathrm{CeCoIn}}_{5}$ suggests a notably more localized nature of $f$ electrons in the compound.

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