Band spectrum transformation andTcvariation in theLa2−x

Two Pseudogap Behavior in La2-xSrxCuO4: Thermoelectric Power at High Temperature

“…Figure 2 shows the temperature dependence of TEP for LSCO for T C < T < 700 K. Below 300 K our results are in good agreement with other published data on polycrystalline and single-crystal samples [19,29,30]. For lightly doped sample (x = 0.05), the TEP rises towards a maximum near T p and decreases linearly with temperature up to 700 K. Elizarova et al [22] suggested that at low doping level, the impurity states due to Sr doping serve as the midgap states. On the basis of their phenomenological model, this midgap band is almost localized and very narrow at low doping, so that TEP is saturated at relatively low temperature near 300 K. However, our TEP re- sults show that linear-T dependence is extended up to 700 K, which indicates that this model is not appropriate to understand TEP of lightly doped LSCO.…”

“…S 300 K data in our samples show consistent behavior compared with the reported data [19][20][21][22][23]. S 300 K is logarithmically decreased with Sr concentration down to ∼1 µ V/K for x = 0.275.…”

Saturation of resistivity and Kohler's rule in Ni-dopedLa1.85Sr0.15CuO4cuprate

“…The obtained asymmetry factor b = −(0.06-0.08), although very small, is essential for good fits. The ratio F of n to the total number od states n DOS is slightly above halffilling (0.51-0.53) and thus consistent with the sign of S and in good agrement with literature data for x=0.15 LSCO [40,42] crosses the conduction-band upper edge at y ≈ 0.15. The band-filling F does not show any obvious y-dependence.…”

“…The S(T ) curves in La 1.85 Sr 0.15 Cu 1−y Ni y O 4 retain the specific features of thermopower in underdoped cuprates: the initial strong growth of S with increasing T is followed by a broad maximum and subsequent slight decrease in S [39]. We find that the phenomenological asymmetrical narrow-band model [40] describes the experimental S(T ) curves very well at high T , above their maximum at T max . In this model, a sharp density-of-states peak with the effective bandwidth W D is located near The parameter a2 as a function of inverse carrier concentration (open circles).…”

On the transformation of the normal-state band spectrum of Tl-based HTSC’s with increasing number of CuO2 layers and doping level

“…As shown in our previous publications, this model, based on the assumption of the existence of a narrow density-of-states (DOS) peak in the band structure of HTSC-materials, allows one to describe all the features of the normal-state transport properties of yttrium-, lanthanum-, bismuth-and mercurybased superconductors [8][9][10]15,[19][20][21][22]. In the framework of this model, approximating the DOS D(e) and the differential conductivity, r(e), functions by rectangles of different widths, one can obtain analytical expressions for the chemical potential, l, and the transport coefficients.…”