Effects of electronic correlations on the thermoelectric power of the cuprates

Abstract

We show that important anomalous features of the normal-state thermoelectric power S of high-Tc materials can be understood as being caused by doping dependent short-range antiferromagnetic correlations. The theory is based on the fluctuation-exchange approximation applied to Hubbard model in the framework of the Kubo formalism. Firstly, the characteristic maximum of S as function of temperature can be explained by the anomalous momentum dependence of the single-particle scattering rate. Secondly, we discuss the role of the actual Fermi surface shape for the occurrence of a sign change of S as a function of temperature and doping.PACS numbers: 71.27.+a, 74.25.Fy, The thermoelectric power (TEP), S, of the high-T c materials in the normal state exhibits anomalous features [1][2][3][4] that are not well understood at present. For example, its temperature dependence shows a characteristic maximum that can be found in all optimally and underdoped cuprates, which is in contrast to the conventional linear-T behavior of a weakly correlated Fermi liquid. Furthermore, a better understanding of the doping dependence, which has been shown to be universal for a large class of high-T c materials [1], is needed.Experimentally, the TEP is positive for the underdoped cuprates. It increases rapidly as a function of temperature, reaches a maximum S ⋆ at a temperature T ⋆ and falls off almost linearly with temperature. The size of the maximum S ⋆ and the value of T ⋆ decrease rapidly with increasing doping, while the slope for the fall-off at T > T ⋆ is almost independent of the doping concentration. The TEP of nearly optimally doped materials shows a similar behavior below room temperature, but the over-all size of the TEP is reduced. Furthermore, the TEP for most of the optimally doped samples changes sign at approximately room temperature [1]. For overdoped samples, the behavior of the TEP is very different: It is negative and decreases linearly with increasing temperature. At present there are only two classes of high-T c materials that do not follow this generic trend, namely La 2−x Sr x CuO 4 (LSCO) and YBa 2 Cu 3 O 7−δ (YBCO). For LSCO the TEP remains positive in the overdoped regime, where it exhibits a maximum of decreasing height for increasing hole concentration [4], whereas YBCO shows a negative TEP in the overdoped regime but with a positive slope at temperatures T > T ⋆ [1,2]. Recently Bernhard and Tallon [2] presented strong experimental evidence that the chain contribution is responsible for this non-generic TEP of YBCO while the contribution of the CuO 2 planes follows the generic behavior.Theoretically, important open problems concerning the characteristic behavior of the TEP remain, although there have been several attempts to explain this behavior, ranging from the van Hove scenario [5,6] to phonon drag effects [7]. The most important open questions are the physical origin of the characteristic temperature scale T ⋆ and of the doping dependence of the sign of S.In this paper, we demonstrate that short-range anti...

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