N\'eel and singlet RVB orders in the t-J model
  The N\'eel and the singlet RVB orders of the {\it t-J} model in a 2D square lattice are studied in the slave-boson mean-field approximation. It is shown that the N\'eel order parameter takes the maximum value at the finite temperature and disappear at the lower temperature for a certain range of doping. It is also shown that the N\'eel and the singlet RVB orders coexist at low temperature. This suggests the possibility of the coexistence of the N\'eel and the superconducting orders. 
M. Inaba, H. Matsukawa, M. Saitoh and H. Fukuyama