Nernst Effect: Evidence of Local Kondo Scattering in Heavy Fermions

A distinctly temperature-dependent Nernst coefficient, $\nu$, which is strongly enhanced over that of ${\mathrm{LaCu}}_2{\mathrm{Si}}_2$, is observed between $T=2$ and 300 K for ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ and ${\mathrm{Ce}}_{0.8}{\mathrm{La}}_{0.2}{\mathrm{Cu}}_2{\mathrm{Si}}_2$. The enhanced $\nu (T)$ is determined by the asymmetry of the on-site Kondo (conduction electron $-4f$ electron) scattering rate. Taking into account the measured Hall mobility, ${\mu }_H$, the highly unusual thermopower, $S$, of these systems can be semiquantitatively described by $S(T)=-\nu (T)/{\mu }_H(T)$, which explicitly demonstrates that the thermopower originates from the local Kondo scattering process over a wide temperature range from far above to well below the coherence temperature ($\approx 20\mathrm{K}$ for ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$). Our results suggest that the Nernst effect can act as a proper probe of local charge-carrier scattering. This promises to impact on exploring the unconventional enhancement of the thermopower in correlated materials suited for potential applications.