ar X iv : c on d - m at / 9 60 10 31 v 3 2 9 Fe b 19 96 Temperature dependence of the electron chemical potential in YBa

We study the behaviour of the electronic chemical potential in YBa2Cu3O6+δ near the superconducting transition using the spin-wave exchange theory of pairing. We find that the experimental value of the jump in the temperature derivative of the chemical potential is inconsistent with the theoretical value calculated under the assumption of constant hole concentration. It is suggested that charge transfer between chains and planes takes place and corresponding calculations are done. Typeset using REVTEX 1 The temperature dependence of the chemical potential near the superconducting transition has attracted some attention recently [1–8]. It has been shown in several models that there is a jump in the temperature derivative of the chemical potential. In Ref. [1], in a simple BCS model with quadratic dispersion and s-wave pairing, the relationship between the chemical potential in the superconducting state μs and the chemical potential in the normal state μn was found to be μs = μn − ∆ 4μn , (1) where ∆ is the gap at the Fermi surface. Near the critical point ∆ ∝ √ Tc − T , and from Eq. (1) it follows that the temperature dependence of the chemical potential is not smooth. This effect has been observed experimentally [8]. Measurements of the work function of the YBa2Cu3O6+δ compound with the critical temperature of 90K gave d(μn − μs) dT ∣