title: Direct measurement of the upper critical field in cuprate superconductors.
abstract: 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.
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: G
authors: G
authors: Grissonnanche
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: O
authors: O
authors: Cyr-Choinière
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: F
authors: F
authors: Laliberté
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: S
authors: S
authors: René de Cotret
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: A
authors: A
authors: Juneau-Fecteau
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: S
authors: S
authors: Dufour-Beauséjour
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: M-È
authors: MÈ
authors: Delage
authors: 1] Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 [2].
authors: D
authors: D
authors: LeBoeuf
authors: 1] Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 [2].
authors: J
authors: J
authors: Chang
authors: Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.
authors: B J
authors: BJ
authors: Ramshaw
authors: 1] Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1 [2] Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8.
authors: D A
authors: DA
authors: Bonn
authors: 1] Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1 [2] Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8.
authors: W N
authors: WN
authors: Hardy
authors: 1] Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1 [2] Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8.
authors: R
authors: R
authors: Liang
authors: Superconductivity Research Laboratory, ISTEC, Yokohama, Kanagawa 223-0051, Japan.
authors: S
authors: S
authors: Adachi
authors: 1] H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK [2].
authors: N E
authors: NE
authors: Hussey
authors: Laboratoire National des Champs Magnétiques Intenses, Toulouse 31400, France.
authors: B
authors: B
authors: Vignolle
authors: 1] Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8 [2] Laboratoire National des Champs Magnétiques Intenses, Toulouse 31400, France.
authors: C
authors: C
authors: Proust
authors: Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
authors: M
authors: M
authors: Sutherland
authors: Laboratoire National des Champs Magnétiques Intenses, Grenoble, France.
authors: S
authors: S
authors: Krämer
authors: National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA.
authors: J-H
authors: JH
authors: Park
authors: National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA.
authors: D
authors: D
authors: Graf
authors: Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
authors: N
authors: N
authors: Doiron-Leyraud
authors: 1] Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 [2] Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8.
authors: Louis
authors: L
authors: Taillefer