Temperature dependence of the hole density in high-TC superconductors Bi2−yPbySr2CaCu2O8+δ

Abstract

One of the most puzzling anomalies of high-TC cuprates is the strong temperature dependence of the Hall coefficient (RH) and the hole density (nH). Gor’kov and Teitel’baum (GT) proposed by using experimental data of La2−xSrxCuO4 (LSCO) a two fluid model. The number of holes per Cu atom nH, changes with temperature according to nH(T,x)=n0(x)+n1(x)exp(−Δ(x)/T) [1]. To clarify the temperature dependence of nH we have determined nH from X-ray absorption spectra (XAS) at the CuL3 edge for nearly optimum and slightly underdoped Bi2−yPbySr2CaCu2O8+δ single crystals yielding directly the absolute value of nH in the CuO2 planes and also its change with temperature nH(T). It shows pronounced structures between 10K and 300K. The temperature dependence puts constraints to the applicability of previously developed models: (i) the two-band model without any explicit temperature dependence and (ii) the formula of GT, because the latter is not able to fit our data over the whole temperature range from 10K to 300K. Instead the thermal behavior of nH proposes a function with at least three terms, i.e. a third term added to the formula of GT is of exponential form ∼T3/2.