Greg Boebinger (Prof. au National High Magnetic Field Laboratory and Florida State University, USA) présentera un séminaire intitulé : "Heat capacity of underdoped YBCO through the magnetic-field-induced resistive transition : d-Wave Superconductor or Fermi Liquid or Both or Neither" Vendredi 25 mai à 10h Salle Louis Weil E424
The underlying physics of the magnetic-field-induced resistive state in lightly doped high temperature cuprate superconductors remains a mystery. One interpretation is that the application of magnetic field destroys the d-wave superconducting gap, uncovering a Fermi surface that behaves as a Fermi Liquid. Another view is that an applied magnetic field destroys long range superconducting phase coherence, but the superconducting gap amplitude survives. Our measurements of the specific heat of Y Ba2Cu3O6.56 in magnetic fields to 45T support the second scenario. We measure the quasi-particle density of states from the superconducting state well into the magnetic-field-induced resistive state. At very high magnetic fields the specific heat exhibits both the conventional temperature dependence and quantum oscillations expected for a Fermi liquid. On the other hand, the quasi-particle density of states increases as the square-root of magnetic field and persists smoothly through the zero-resistance transition. This clearly evidences the fully developed d-wave superconducting gap over the entire magnetic field range measured. Most importantly, our measurements place a clear and strong constraint on any thermodynamic theory of the magnetic-field-induced resistive state in underdoped YBCO. A brief survey of other scientific frontiers at the NHMFL will also be presented. Jokes will be told.
The collaboration includes Scott Riggs, Oskar Vafek and Jon Kemper of the National High Magnetic Field Laboratory and Florida State University ; Jon Betts, Al Bert Migliori and Fedor Balakirev of the National High Magnetic Field Laboratory and Los Alamos National Laboratory ; and W. N. Hardy, Ruixing Liang and Doug Bonn of the University of British Columbia.
Prochain séminaire : Rafik Ballou, mardi 29 mai.