Numerical study on spin and charge degrees of freedom in one-dimensional t-J model

We examined the t-J and the t-t'-J models in one dimension by numerical diagonalization. We introduced and calculated a quantity Q measuring the mixing of the charge and spin degrees of freedom in a wavefunction. In the case of t'/vertical stroketvertical stroke=0, Q for the ground state vanishes in the limit of J/vertical stroketvertical stroke→0, corresponding to the well-known perfect separation of the wave function. As J/vertical stroketvertical stroke increases, Q increases rapidly for small J/vertical stroketvertical stroke and becomes very close to the value of the Gutzwiller wavefunction for J/vertical stroketvertical stroke=2. In the case of finite t'/vertical stroketvertical stroke, Q is finite even if J/vertical stroketvertical stroke=0, showing that the hole motion drived by the second neighbor hopping t' effectively exchanges electronic spins or mixes the spin and the charge degrees of freedom. (orig.)