Strongly correlated properties of the thermoelectric cobalt oxide Ca 3 Co 4 O 9

By P. Limelette, V. Hardy, P. Auban-Senzier, D. Jérome, D. Flahaut, S. Hébert, R. Frésard, C. Simon, J. Noudem, A. Maignan. 2005

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We have performed both in-plane resistivity, Hall effect, and specific heat measurements on the thermoelectric cobalt oxide ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$. Four distinct transport regimes are found as a function of temperature, corresponding to a low temperature insulating one up to ${T}_{\mathit{min}}\ensuremath{\approx}63\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a strongly correlated Fermi liquid up to ${T}^{*}\ensuremath{\approx}140\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, with $\ensuremath{\rho}={\ensuremath{\rho}}_{0}+A{T}^{2}$ and $A\ensuremath{\approx}3.63\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\ensuremath{\Omega}\phantom{\rule{0.2em}{0ex}}\mathrm{cm}∕{\mathrm{K}}^{2}$, followed by an incoherent metal with ${k}_{F}l\ensuremath{\leqslant}1$ and a high temperature insulator above ${T}^{**}\ensuremath{\approx}510\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The specific heat Sommerfeld coefficient $\ensuremath{\gamma}=93\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕(\mathrm{mol}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2})$ confirms a rather large value of the electronic effective mass and fulfils the Kadowaki-Woods ratio $A∕{\ensuremath{\gamma}}^{2}\ensuremath{\approx}0.45\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\ensuremath{\Omega}\phantom{\rule{0.2em}{0ex}}\mathrm{cm}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2}∕({\mathrm{mJ}}^{2}\phantom{\rule{0.2em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}2})$. Resistivity measurements under pressure reveal a decrease of the Fermi liquid transport coefficient A with an increase of ${T}^{*}$ as a function of pressure while the product $A{({T}^{*})}^{2}∕{b}_{2}$ remains constant and of order $h∕{e}^{2}$. Both thermodynamic and transport properties suggest a strong renormalization of the quasiparticles coherence scale of order ${T}^{*}$ that seems to govern also thermopower.

Subfields: Condensed Matter Physics, Materials Chemistry

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