Prominent electron-hole asymmetry in thermoelectric transport of LaCoO${}_3$

Abstract

We have measured the electrical resistivity and the thermopower of the electron-doped perovskite cobaltites LaCo${}_{1-y}$Te${}_y$O${}_3$. In contrast to the hole-doped systems such as metallic ferromagnets La${}_{1-x}{M}_x$CoO${}_3$ ($M$ = Ca, Sr, Ba), the electron-doped samples show an insulating behavior even in a heavily doped range due to a spin-state blockade mechanism that an electron hopping from high-spin Co${}^{2+}$ to low-spin Co${}^{3+}$ site is energetically suppressed. We find that, despite the electron doping, the thermopower shows relatively large positive values above $y=0.05$, strikingly distinct from the hole-doped case where it comes close to zero with doping. This prominent electron-hole asymmetry seen in the thermopower originates from a bipolar conduction which consists of a slight amount of mobile holes and the main immobile electrons, demonstrating an impact of spin-state blockade on thermoelectric transport.

6 pages, 4 figures

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Cited by in corpus (1)

• Carrier filtering effect for enhanced thermopower in a body-centered tetragonal ruthenate