Excited States Beyond Mott Gap in Half-Filled-Band Hubbard Model

In connection with recent experiments on excitation in which Mott insulators change to conductors, we study the properties of excited states beyond gap as quasi-stationary for a two-dimensional Hubbard (t-t'-U) model at half filling. A variational Monte Carlo method is used trial wave functions paramagnetic or normal (PM), superconducting dx2-y2-wave (d-SC), isotropic s-wave, and extended s-wave symmetries, antiferromagnetic (AF) states. The are generated by imposing minimum number doubly occupied sites (doublons) D_L lowest-energy For U>W (W: band width), d_L=D_L/Ns (Ns: sites) corresponds intensity. It found that AF state most stable among treated d_L<0.14 insulating. PM d-SC become conductive over threshold d_Lc, conduction caused unbound doublons holons (empty sites). arises d_L>0.14, but always hidden state. s-wave-type not stabilized any parameter set.