Baptiste Vignolle

Quantum oscillations in an overdoped high-Tc superconductor

The nature of the metallic phase in the high-transition-temperature (high-Tc) copper oxide superconductors, and its evolution with carrier concentration, has been a long-standing mystery. A central question is how coherent electronic states, or quasiparticles, emerge from the antiferromagnetic insulator with doping. Recent quantum oscillation experiments on lightly doped copper oxides have shown evidence for small pockets of Fermi surface, the formation of which has been associated with the opening of the pseudogap—an anisotropic gap in the normal state excitation spectrum of unknown origin. As the doping is increased, experiments suggest that the full Fermi surface is restored, although the doping level at which the pseudogap closes and the nature of the electronic ground state beyond this point have yet to be determined. Here we report the observation of quantum oscillations in the overdoped superconductor Tl2Ba2CuO6+δ that show the existence of a large Fermi surface of well-defined quasiparticles covering two-thirds of the Brillouin zone. These measurements confirm that, in overdoped superconducting copper oxides, coherence is established at all Fermi wavevectors, even near the zone boundary where the pseudogap is maximal and electronic interactions are strongest; they also firmly establish the applicability of a generalized Fermi-liquid picture on the overdoped side of the superconducting phase diagram.

Small Fermi Surface Pockets in Underdoped High Temperature Superconductors: Observation of Shubnikov-de Haas Oscillations in YBa2Cu4O8

A. F. Bangura, J. D. Fletcher, A. Carrington, J. Levallois, M. Nardone, B. Vignolle , P. J. Heard, N. Doiron-Leyraud, D. LeBoeuf, L. Taillefer, S. Adachi, C. Proust and N. E. Hussey H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, BS8 1TL, United Kingdom. Laboratoire National des Champs Magnétiques Pulsés, UMR CNRS-UPS-INSA 5147, Toulouse, France. Département de physique and RQMP, Université de Sherbrooke, Sherbrooke, J1K 2R1, Canada. and Superconducting Research Laboratory, International Superconductivity Center, Shinonome 1-10-13, Tokyo 135, Japan. (Dated: February 1, 2008)

Lifshitz critical point in the cuprate superconductor YBa2Cu3Oy from high-field Hall effect measurements

The Hall coefficient RH of the cuprate superconductor YBa 2Cu3Oy was measured in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152 in the underdoped regime. In fields large enough to suppress superconductivity, RH(T) is seen to go from positive at high temperature to negative at low temperature, for p0.08. This change of sign is attributed to the emergence of an electron pocket in the Fermi surface at low temperature. At p<0.08, the normal-state R H(T) remains positive at all temperatures, increasing monotonically as T→0. We attribute the change of behavior across p=0.08 to a Lifshitz transition, namely a change in Fermi-surface topology occurring at a critical concentration pL=0.08, where the electron pocket vanishes. The loss of the high-mobility electron pocket across pL coincides with a tenfold drop in the conductivity at low temperature, revealed in measurements of the electrical resistivity ρ at high fields, showing that the so-called metal-insulator crossover of cuprates is in fact driven by a Lifshitz transition. It also coincides with a jump in the in-plane anisotropy of ρ, showing that without its electron pocket, the Fermi surface must have strong twofold in-plane anisotropy. These findings are consistent with a Fermi-surface reconstruction caused by a unidirectional spin-density wave or stripe order.

Evolution of the Fermi Surface of BaFe2(As1-xPx)2 on Entering the Superconducting Dome

Using the de Haas-van Alphen effect we have measured the evolution of the Fermi surface of BaFe2(As1-xPx){2} as a function of isoelectric substitution (As/P) for 0.41<x<1 (T{c} up to 25 K). We find that the volumes of electron and hole Fermi surfaces shrink linearly with decreasing x. This shrinking is accompanied by a strong increase in the quasiparticle effective mass as x is tuned toward the maximum T{c}. These results are not explained by simple band structure calculations, and it is likely that these trends originate from the same many-body interactions which give rise to superconductivity.

Direct measurement of the upper critical field in cuprate superconductors

In the quest to increase the critical temperature Tc of cuprate superconductors, it is essential to identify the factors that limit the strength of superconductivity. The upper critical field Hc2 is a fundamental measure of that strength, yet there is no agreement on its magnitude and doping dependence in cuprate superconductors. Here we show that the thermal conductivity can be used to directly detect Hc2 in the cuprates YBa2Cu3Oy, YBa2Cu4O8 and Tl2Ba2CuO6+δ, allowing us to map out Hc2 across the doping phase diagram. It exhibits two peaks, each located at a critical point where the Fermi surface of YBa2Cu3Oy is known to undergo a transformation. Below the higher critical point, the condensation energy, obtained directly from Hc2, suffers a sudden 20-fold collapse. This reveals that phase competition—associated with Fermi-surface reconstruction and charge-density-wave order—is a key limiting factor in the superconductivity of cuprates.

de Haas-van Alphen Oscillations in the Underdoped High-Temperature Superconductor YBa2Cu3O6.5

Cyril Jaudet, David Vignolles, ∗ Alain Audouard, Julien Levallois, D. LeBoeuf, Nicolas Doiron-Leyraud, B. Vignolle, M. Nardone, A. Zitouni, Ruixing Liang, 4 D.A. Bonn, 4 W.N. Hardy, 4 Louis Taillefer, 4 and Cyril Proust † Laboratoire National des Champs Magnétiques Pulsés (CNRS-UPS-INSA), Toulouse, France Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Canada Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada Canadian Institute for Advanced Research, Toronto, Canada (Dated: May 13, 2008)

Angle dependence of quantum oscillations in YBa2Cu3O6.59 shows free-spin behaviour of quasiparticles

A genetic-algorithm approach to analysing quantum oscillations in a high-temperature superconductor reveals that quasiparticles behave as nearly free spins—split into spin-up and spin-down populations, known as the Zeeman effect.

Hall, Seebeck, and Nernst Coefficients of Underdoped HgBa_{2}CuO_{4+δ}: Fermi-Surface Reconstruction in an Archetypal Cuprate Superconductor

A key to understanding high-temperature superconductivity in cuprates lies in the identification of competing electronic phases in these materials. In YBa

Evidence for a small hole pocket in the Fermi surface of underdoped YBa2Cu3Oy

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Electronic instability in bismuth far beyond the quantum limit

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