Interlayer coupling and the thermopower of cuprate superconductors
- Center for Materials Science and Engineering, ETC 9.104, University of Texas at Austin, Austin, Texas 78712 (United States)
A review of the extant literature on the thermopower (TEP) of the cuprate superconductors reveals a transition from polaronic to homogeneous itinerant electron behavior with increasing hole concentration in the CuO{sub 2} sheets. Superconductivity appears at the compositions of crossover from one regime to the other, and the normal state of the superconductors retains a heterogeneous electronic structure of mobile hole-rich and hole-poor domains, which introduces both a statistical and a transport component to the Seebeck coefficient. A primary manifestation of the transport component is an enhancement term {delta}{alpha}({ital T}) having a maximum at a {ital T}{sub max}=100{endash}140 K, which is characteristic of a strong coupling of the charge carriers to optical rather than acoustic phonons. Comparison of the TEP for La{sub 1.85}Sr{sub 0.15}CuO{sub 4} vs La{sub 0.85}Sr{sub 1.15}GaCuO{sub 5} and La{sub 1.8}Sr{sub 0.2}CaCu{sub 2}O{sub 6+{delta}} vs Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} indicates that an increase in the {bold c}-axis coupling between neighboring CuO{sub 2} sheets increases the size of the polaron or hole-rich domains in the underdoped compositions, thereby lowering the room-temperature value of the Seebeck coefficient {alpha}(300 K) and increasing the magnitude of {delta}{alpha}({ital T}). These observations implicate a strong elastic component, enhanced by electron-lattice interactions, in the {bold c}-axis coupling as well as in the formation of larger nonadiabatic polarons and their interactions within the CuO{sub 2} planes. They also signal that caution must be exercised in any application of a {open_quote}{open_quote}universal plot{close_quote}{close_quote} of {alpha}(300 K) versus hole concentration {ital p} per Cu atom in a CuO{sub 2} plane to obtain a value of {ital p} from TEP data. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 388337
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 17 Vol. 54; ISSN 0163-1829; ISSN PRBMDO
- Country of Publication:
- United States
- Language:
- English
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