Positive Seebeck Coefficient in Highly Doped La2−xSrxCuO4 (x = 0.33); Its Origin and Implication

We present a study of the thermoelectric (Seebeck and Nernst) response in heavily overdoped, non-superconducting La1.67Sr0.33CuO4. In spite of the electron-like curvature of the Fermi surface, the Seebeck coefficient is positive at low temperatures. Such a feature, previously observed in copper, silver, gold and lithium, is caused by a non-trivial energy dependence of the scattering time. We argue that this feature implies a strong asymmetry between the lifetime of occupied and unoccupied states along the zone diagonals and such an electron–hole asymmetry impedes formation of Cooper pairs along the nodal direction in the superconducting ground state emerging at lower doping levels.