Hall, Seebeck, and Nernst Coefficients of Underdoped HgBa2CuO4+delta : Fermi-Surface Reconstruction in an Archetypal Cuprate Superconductor
Résumé
Charge-density-wave order has been observed in cuprate superconductors whose crystal structure breaks the square symmetry of the CuO2 planes, such as orthorhombic YBa2Cu3Oy (YBCO), but not so far in cuprates that preserve that symmetry, such as tetragonal HgBa2CuO4+delta (Hg1201). We have measured the Hall (R-H), Seebeck (S), and Nernst (nu) coefficients of underdoped Hg1201 in magnetic fields large enough to suppress superconductivity. The high-field R-H(T) and S(T) are found to drop with decreasing temperature and become negative, as also observed in YBCO at comparable doping. In YBCO, the negative R-H and S are signatures of a small electron pocket caused by Fermi-surface reconstruction, attributed to charge-density-wave modulations observed in the same range of doping and temperature. We deduce that a similar Fermi-surface reconstruction takes place in Hg1201, evidence that density-wave order exists in this material. A striking similarity is also found in the normal-state Nernst coefficient nu(T), further supporting this interpretation. Given the model nature of Hg1201, Fermi-surface reconstruction appears to be common to all hole-doped cuprates, suggesting that density-wave order is a fundamental property of these materials.