Four-band model for oxygen holes in copper oxide superconductors. I. Quasiparticles.

Abstract

All the high-temperature superconductors have copper oxide planes with strong antiferromagnetic correlations. In many of these, the charge is carried by quasiparticles which are based on holes that move on the oxygen ions. We study the effect of the antiferromagnetic background of the Cu spins in the CuO{sub 2} planes on the spectrum of the mobile quasiparticles. We consider several possible quasiparticles, which involve the spin of the hole and the spins of the two neighboring copper ions. For each quasiparticle we obtain, using tight-binding methods, four energy bands. We find that the favored charge carrier is a spin 1/2 quasiparticle. The minimum of the lowest energy band is at the points {bold k}=(0,{plus minus}{pi}/2{ital {tilde a}}) and {bold k}=({plus minus}{pi}/2{ital {tilde a}},0), where the {ital x} and {ital y} directions are along the nearest-neighbors oxygen-oxygen bonds (of length {ital {tilde a}}) in the CuO{sub 2} plane. The effective mass is less than 3.7{ital m}{sub {ital e}}, in good agreement with measurements of the London penetration depth for La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4}. It is also consistent with these measurements for the Bi and Tl compounds. However, we obtain conflicting results for YBa{sub 2}Cu{sub 3}O{sub 6+{ital y}}, possibly duemore » to the fact that the CuO chains also superconduct.« less