Nernst and Seebeck Coefficients of the Cuprate SuperconductorYBa2Cu3O6.67: A Study of Fermi Surface Reconstruction

Abstract

The Seebeck and Nernst coefficients S and ν 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, ν becomes independent of field by H ≃ 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and ν/T are both large and negative in the T → 0 limit, with the magnitude and sign of S/T consistent with the small electron-like Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T ) at T ≃ 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.PACS numbers: 74.25.Fy A major hurdle in understanding high-temperature superconductivity is the nature of the pseudogap phase. No consensus has yet been reached on whether this enigmatic phase is a precursor of superconductivity or a second ordered phase [1]. One way to shed light on this question is to study the ground state of the pseudogap phase in the absence of superconductivity, achieved by applying a strong enough magnetic field. This approach has recently revealed a qualitative change in the Fermi surface of cuprates measured via quantum oscillations, from a large hole-like cylinder in the overdoped regime outside the pseudogap phase [2] to a Fermi surface containing small electron-like pockets [3] in the underdoped regime inside the pseudogap phase [3][4][5][6][7]. Because the presence of an electron pocket in the Fermi surface of hole-doped cuprates almost certainly implies that the lattice translational symmetry is broken by some density-wave order [8], it is important to confirm the electron-like nature of the Fermi pocket detected in YBa 2 Cu 3 O y (YBCO), and elucidate the mechanism that causes it to emerge.In this Letter, we show that: 1) the low-temperature Nernst coefficient of YBCO at p = 0.12 is independent of field by H ≃ 30 T, proof that the vortex contribution is negligible by then, and the normal state has been reached; 2) the magnitude and negative sign of the thermopower at low temperature are consistent with the frequency and cyclotron mass of quantum oscillations only if these come from orbits around an electron pocket. From the fact that both the thermopower and the Hall coefficient of YBCO are very similar to those of three cuprate materials exhibiting 'stripe' order, a form of spin/charge density wave, we infer that the Fermi surface of underdoped YBCO also undergoes a reconstruction due to a similar form of spin and/or charge ordering.When a temperature difference ∆T is applied along the x-axis of a metallic sample, a longitudinal voltage V x develops across a length L, and the Seebeck coefficient (or thermopower) is defined as S ≡ V x /∆T . In the presence of a perpendicular magnetic field H (along the z-axis), a transverse voltage V ...

Effective theory of Fermi pockets in fluctuating antiferromagnets

“…Some of the transport data 23,25,26 has been interpreted in terms of the presence of electron pockets in the hole-doped cuprates, for which there is no apparent evidence in the photoemission studies; the latter, however, have only been carried out without a magnetic field.…”

Quantum criticality and the phase diagram of the cuprates

“…Recent thermoelectric and Nernst effect experiments [8] and theory [9,10] have also provided support for the Fermi surface transformations associated with the QCP at x = x m . Associated measurements of the anisotropy in the Nernst co-efficient [11] have been proposed to be explained by the influence of nematic order in the Fermi surface [12]; this nematic order can be regarded as a remnant of a fluctuating SDW state, as is suggested by neutron scattering observations [13].…”

Spin density wave order and fluctuations inMn3Si: A transport study

“…This concerns in addition to the well known quantities resistivity, Hall and Seebeck effects, also the Nernst effect, which came into focus recently because of its sensitivity to subtle Fermi surface changes and fluctuations. [10][11][12][13][14][15][16][17] In this paper we take the impact of SDW ordering on the transport coefficients under scrutiny by investigating the transport properties of the itinerant antiferromagnet Mn 3 Si which undergoes a SDW transition at about 25 K. [18][19][20][21][22] We study in particular the electrical resistivity, thermal conductivity, Hall, Seebeck and Nernst effects in the temperature range from 10 K up to 300 K. Clear anomalies are observed at the SDW transition which confirm it to be at ∼ 22 K and give strong evidence for a large fluctuation regime which extends up to ∼ 200 K in the resistivity, as well as the Seebeck and Nernst effects. We compare our results with other prototype SDW materials, viz.…”