Strongly correlated properties of the thermoelectric cobalt oxide Ca3Co4O9

Abstract

We have performed both in-plane resistivity, Hall effect and specific heat measurements on the thermoelectric cobalt oxide Ca${}_3$Co${}_4$O${}_9$. Four distinct transport regimes are found as a function of temperature, corresponding to a low temperature insulating one up to $T_{min}\approx$63 K, a strongly correlated Fermi liquid up to $T^{\ast }\approx$140 K, with $\rho ={\rho }_0+A{T}^2$ and $A\approx 3.63$ $10^{-2}\mu \Omega cm/K^2$, followed by an incoherent metal with $k_{F}l\le 1$ and a high temperature insulator above T${}^{\ast \ast }\approx$510 K . Specific heat Sommerfeld coefficient $\gamma =93$ mJ/(mol.K${}^2$) confirms a rather large value of the electronic effective mass and fulfils the Kadowaki-Woods ratio $A/{\gamma }^2\approx 0.45$ 10${}^{-5}$ $\mu \Omega cm.K^2/(m{J}^{2}mo{l}^{-2})$. Resistivity measurements under pressure reveal a decrease of the Fermi liquid transport coefficient A with an increase of $T^{\ast }$ as a function of pressure while the product $A(T^{\ast }{)}^2/a$ remains constant and of order $h/e^2$. Both thermodynamic and transport properties suggest a strong renormalization of the quasiparticles coherence scale of order $T^{\ast }$ that seems to govern also thermopower.

5 pages, 6 figures, accepted for publication in Physical Review B