Field-induced incommensurate order for the quasi-one-dimensional XXZ model in a magnetic field

We investigate phase transitions of the quasi-one-dimensional S=1/2 XXZ model in a magnetic field, using bosonization combined with a mean-field treatment of the interchain interaction. We then find that the field-induced incommensurate order is certainly realized in the low-field region, while transverse staggered order appears in the high-field region. On the basis of the result, we discuss the field-induced phase transition recently observed for BaCo2V2O8.