Localized to Itinerant Electronic Transitions in Perovskite-Related Structures
Experiments on several perovskite-related transition-metal oxides at the cross-over from localized to itinerant electronic behavior reveal strong electron coupling not only to static, but also to dynamic oxygen displacements. A discontinuous change in the mean kinetic energy of the electrons results in a first-order transition at the cross-over and a breakdown of the Brinkman-Rice strong-correlation model before long-range magnetic order is stabilized. The superconductive copper oxides appear to stabilize a distinguishable thermodynamic state below a T ℓ ≈ 300 K where a multicenter polaron gas condenses into a polaron liquid that progressively orders into mobile stripes as the temperature is lowered to Tc. It is suggested that itinerant vibronic states are formed as a result of coupling of itinerant electrons to dynamic oxygen displacements along the Cu-O bond axes in the mobile stripes. Such vibronic states would be responsible for a remarkable transfer of spectral weight to states propagating parallel to the bond axes. The transfer of spectral weight is responsible for the anisotropy of the superconductive gap and an enhancement of the thermoelectric power in the interval Tc < T < T ℓ that is uniquely associated with the high- Tc superconductive phenomenon.
KeywordsThermoelectric Power Superconductive Phase Spectral Weight Itinerant Electron Superconductive Copper Oxide
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