Infrared Study of the Order Parameter in YBa2Cu3O7: Analogy to Short Range Ordering in Itinerant Ferromagnets

  • D. van der Marel
  • A. Wittlin
  • H.-U. Habermeier
  • D. Heitmann

Abstract

We report on detailed measurements of the temperature dependence of the infrared reflectivity spectra of YBa2Cu3O7. It is shown that the prominent edge1 at 8k B T c shows practically no energy shift as a function of temperature, whereas the oscillator strength of this feature depends strongly on temperature with a marked critical behavior at the superconducting transition temperature. This behavior coincides with the temperature dependence of the superfluid fraction, which was determined from the spectra using two different methods. A precursor at the same energy position persists at temperatures above T c . If the edge can be interpreted as the characteristic energy required to break up a pair, we arrive at the conclusion that the gap itself can not be considered as an order parameter in this case. The superfluid density on the other hand changes approximately as 1 — (T/T c ) 4. We point out that a remarkable analogy exists to the situation in itinerant magnetism, where short range order persists above the Curie temperature resulting in an exchange splitting that does not vanish2 at T c .

Keywords

Helium Coherence Eter FERRO 

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Copyright information

© Springer Science+Business Media New York 1991

Authors and Affiliations

  • D. van der Marel
    • 1
    • 2
  • A. Wittlin
    • 1
    • 3
    • 4
  • H.-U. Habermeier
    • 1
  • D. Heitmann
    • 1
  1. 1.Max-Planck-Institut für FestkörperforschungStuttgart 80Federal Republik of Germany
  2. 2.Faculty of Applied PhysicsDelft University of TechnologyDelftThe Netherlands
  3. 3.research project RPBP 01.9Institute of Physics PAN PLWarszawaPoland
  4. 4.Katholieke Universiteit NijmegenNijmegenThe Netherlands

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