Contribution to the theory of high-temperature superconductivity in YBa2Cu3O7

✍ Scribed by D. Wechsler; J. Ladik

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 280 KB
• Volume: 71
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1999)71:3<285::aid-qua5>3.0.co;2-#

✦ Synopsis

Applying the wave functions and exciton energies determined and . described in two previous articles for YBa Cu O , we calculated the effective potential 2 3 7 V assuming as a first approximation of the ''two-bands'' model an excitonic mechanism e f f for superconductivity. With the help of the obtained V , we solved the gap equation for e f f Ž . Ž . the cases ⌬ T s 0 and ⌬ T s 0 . We obtained a critical temperature T value of 87 K k c k c 1 1 and ⌬ s 19 meV. These results which give for the ratio 2⌬ rk T s 5.03 agree very ma x ma x B c Ž well with the corresponding experimental values T s 92 K, ⌬ f 20 meV, c m a x . w Ž .x 2⌬ rk T f 5.0 . In investigating the symmetry of the gap as a function of k ⌬ k , ma x B c 1 1

we found a dominantly d 2 2 wave with a small s wave admixture in good agreement

x yy with experiment. It should be mentioned that in this case starting from first-principle Ž band structures no adjustable parameters; the density functional methods still cannot . provide exciton energies , the most important characteristics of the normal and superconducting state of a cuprate high T superconductor were quantitatively calculated c in very good agreement with experiment.