Electronic Structure of the High Tc Superconductors
The high Tc superconductors have one structural element in common, namely CuO2 planes which are lightly doped away from an average valence of Cu2+. In the absence of this doping the planes are in a Mott insulating state with local S = 1/2 moments on each Cu-site. There is considerable evidence both experimental and theoretical supporting the assignment of the extra holes, introduced by doping, to the antibonding O 2p-orbitals. The strong hybridization between these orbitals and the central Cu 3d-orbitals makes it favourable to bind the extra hole with a Cu2+ local moment to form a spin singlet state centred on a CuO4 square. This singlet, however, is mobile and the combination of mobile charged singlets and local spins is described by the so-called t-J model. This has a number of consequences which can be tested experimentally. For example, one can use this model to estimate the hyperfine coupling constants which are measured in NMR experiments. The prediction that the only spin degrees of freedom are the local Cu2+ spins even upon doping can also be tested in NMR experiments.
Philosophical Transactions of the Royal Society of London Series A
- Pub Date:
- March 1991