Dynamic exponent of t-J and t-J-W model

Drude weight of optical conductivity is calculated at zero temperature by exact diagonalization for the two-dimensional t-J model with the two-particle term, W. For the ordinary t-J model with W=0, the scaling of the Drude weight D ∝ δ² for small doping concentration δ is obtained, which indicates anomalous dynamic exponent z=4 of the Mott transition. When W is switched on, the dynamic exponent recovers its conventional value z=2. This corresponds to an incoherent-to-coherent transition associated with the switching of the two-particle transfer.