Nernst and Seebeck Coefficients of the Cuprate Superconductor YBa2Cu3O6.67: A Study of Fermi Surface Reconstruction

The Seebeck and Nernst coefficients S and v of the cuprate superconductor YBa2Cu3Oy (YBCO) were measured in a single crystal with doping p = 0.12 in magnetic fields up to H = 28 T. Down to T = 9 K, v becomes independent of field by H similar or equal to 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and v/T are both large and negative in the T -> 0 limit, with the magnitude and sign of S/T consistent with the small electronlike Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T) at T similar or equal to 50 K is remarkably similar to that observed in La2-xBaxCuO4, La2-x-yNdySrxCuO4, and La2-x-yEuySrxCuO4, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO.