Strongly correlated properties of the thermoelectric cobalt oxide Ca 3 Co 4 O 9
Résumé
We have performed both in-plane resistivity, Hall effect, and specific heat measurements on the thermoelectric cobalt oxide Ca3Co4O9. Four distinct transport regimes are found as a function of temperature, corresponding to a low temperature insulating one up to T-min approximate to 63 K, a strongly correlated Fermi liquid up to T-*approximate to 140 K, with rho=rho(0)+AT(2) and A approximate to 3.63x10(-2) mu Omega cm/K-2, followed by an incoherent metal with k(F)l <= 1 and a high temperature insulator above T-**approximate to 510 K. The 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)approximate to 0.45x10(-5) mu Omega cm K-2/(mJ(2) mol(-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.
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