Abstract
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+d (Hg1201). We have measured the Hall (R_H), Seebeck (S), and Nernst 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, 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.
Highlights
In YBCO, there is compelling evidence that the negative RH and S at low temperature come from a small electron Fermi surface
We deduce that the Fermi surface of underdoped Hg1201 at low temperature contains an electron pocket. This fact implies that the Fermi surface is reconstructed relative to the topology of cuprates at high doping, namely, a single large holelike cylinder, as observed in the single-layer tetragonal cuprate Tl2Ba2CuO6þ at p ’ 0:25 [25,26,27]
Summary and outlook.—Our high-field measurements of Hall and Seebeck coefficients in the tetragonal single-layer cuprate Hg1201 reveal that its normal-state Fermi surface undergoes a reconstruction in the underdoped regime at low temperature, which produces an electron pocket
Summary
With decreasing temperature, they both start to fall below about T ’ 50 K to eventually become negative below T0 1⁄4 10 Æ 1 K These findings are our central result: The low-temperature high-field normal state of Hg1201 has negative Hall and Seebeck coefficients. In YBCO, there is compelling evidence that the negative RH and S at low temperature come from a small electron Fermi surface This evidence includes quantum oscillations [9,24] with a frequency F and mass m?, which, at this doping, account precisely for the normal-state Seebeck coefficient S at T ! This fact implies that the Fermi surface is reconstructed relative to the topology of cuprates at high doping, namely, a single large holelike cylinder, as observed in the single-layer tetragonal cuprate Tl2Ba2CuO6þ at p ’ 0:25 [25,26,27]
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