Accession Number:

ADA297287

Title:

Temperature Dependence of Large Polaron Superconductivity.

Descriptive Note:

Technical rept.,

Corporate Author:

MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB

Personal Author(s):

Report Date:

1995-07-18

Pagination or Media Count:

27.0

Abstract:

The theory based on covalent electron transfer CET between the dsub x2sub-y2 orbitals of mixed-valence Cu ions that was introduced previously to explain the variation of critical temperature Tc with chemical composition and the temperature dependence of high-Tc superconductor properties is modified to reflect lattice-vibration scattering of the large polarons that dominate the electrical conductivity of these compounds at low temperatures. One result of this refinement is a clearer picture of the dependence of electron hopping activation energy on crystal-field parameters. A generalization of the earlier exponential two-fluid model is introduced to describe more accurately the high rate of change in supercarrier density with temperatures in the regime where T approaches Tc. This new model can provide additional insights from the fitting of theory to data. At the lowest temperatures, supercarrier densities may be approximated by a linear function of temperature if Tc values are large. For lower-Tc superconductors the dependence is more typically exponential. With these improvements, precise fits to penetration depth versus temperature measurements for high-purity YBCO single crystals were obtained, as well as more accurate agreement with critical transport current density versus temperature data for thin films. Projections of critical current densities as a function of reduced temperature t TTc are offered for the highest Tc materials predicted by this theory. Parameter values desired for optimum superconductor properties are reexamined. jg p.4

Subject Categories:

  • Inorganic Chemistry
  • Physical Chemistry
  • Crystallography
  • Electricity and Magnetism
  • Atomic and Molecular Physics and Spectroscopy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE