Study of Holon Pair Condensation Based on the U(1) Slave Boson Approach   to a Modified t-J Hamiltonian
  In order to obtain a reasonable phase diagram involving hole-pair condensation for hole-doped cuprate systems, we propose a modified t-J Hamiltonian in which a Coulomb repulsion term between nearest neighbor holes is considered. We show from the investigation of free energy that holon pair condensation can occur as a result of symmetry breaking. In addition, we introduce a possibility of supersymmetry condition at $T=0K$ in the intermediate region between the antiferromagnetic phase and the superconducting phase. 
Sung-Sik Lee, Sung-Ho Suck Salk