High-temperature superconductivity: A variational Monte Carlo study
A variational Monte Carlo simulation and the renormalised mean field theory analysis of the t - J model for the possible high temperature superconducting mechanisms are presented. Several phases for the t-J model have been considered-RVB (Resonant Valence Bond) state (d-wave, s-wave, s+d wave, s+id wave), SFP (Staggered Flux Phase) state state, the mixing of the SDW (Spin Density Wave) state and the RVB state and the mixing of the RVB and the SFP state. The mean field theory analysis suggested antiferromagnetic order at half filling, the d-wave RVB state at away from half filling for its better kinetic energy and the possible SFP phase with the help of the positive nearest neighbor Coulomb interaction. From our variational Monte Carlo simulation, we include the three site term of the t - J model and the nearest neighbor and the next to nearest neighbor Coulomb interaction. We found that the antiferromagnetic state is favored at very small hole doping ({le}5%), which is consistent with the experimental works on the 214 compounds. The d-wave RVB state is favored at hole doping less than 10% and the d-wave picture is also favored by many other calculations. However, at 10% hole doping or higher, we found a phase transition from the d-wave state to the s+id wave state. The existence of two superconducting temperatures of 123 compounds (60 K and 90 K) may be a plausible signature for this phase transition. The possibility of the SFP phase has been carefully examined. We tend to rule out its candidacy as the ground state for the t - J model except at very limited parameter space. The simulated spin coherence length shows the proper relation with the hole concentration as is indicated by the neutron scattering experiment. The methodology we applied here has been explained in detail and the canonical transformation from the Hubbard model to the t - J model has also been presented. Some selected experimental facts have been organized and discussed.
- Research Organization:
- Univ. of Wisconsin, Madison, WI (United States)
- OSTI ID:
- 114785
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1992
- Country of Publication:
- United States
- Language:
- English
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