We report a systematic study of temperature- and field-dependent charge ($\boldsymbol{ \rho}$) and entropy ($\mathbf{ S}$) transport in the heavy-fermion superconductor CeIrIn$_5$. Its large positive thermopower $S_{ xx}$ is typical of Ce-based Kondo lattice systems, and strong electronic correlations play an important role in enhancing the Nernst signal $S_{ xy}$. By separating the off-diagonal Peltier coefficient $\alpha_{ xy}$ from $S_{ xy}$, we find that $\alpha_{ xy}$ becomes positive and greatly enhanced at temperatures well above the bulk $T_c$. Compared with the non-magnetic analog LaIrIn$_5$, these results suggest vortexlike excitations in a precursor state to unconventional superconductivity in CeIrIn$_5$. This study sheds new light on the similarity of heavy-fermion and cuprate superconductors and on the possibility of states not characterized by the amplitude of an order parameter.
Categories: cond-mat.str-el cond-mat.mtrl-sci cond-mat.supr-con