Effects of a magnetic field on the one-dimensional spin-orbital model

We study the effects of a uniform magnetic field on the one-dimensional spin-orbital model in terms of effective field theories. Two regions are examined: one around the SU(4) point (J=K/4) and the other with K<<J. We found that when $J\leq K/4$, the spin and orbital correlation functions exhibit power-law decay with nonuniversal exponents. In the region with J>K/4, the excitation spectrum has a gap. When the magnetic field is beyond some critical value, a quantum phase transition occurs. However, the correlation functions around the SU(4) point and the region with K<<J exhibit distinct behavior. This results from different structures of excitation spectra in both regime.Comment: 22 pages, no figure