Field-induced incommensurate order in spin ladder with ring exchange

The exact diagonalization study on the magnetization process of the S=1/2 spin ladder system revealed that the incommensurate spin correlation parallel to H would be possibly dominant around half the saturation magnetization, with the ring exchange. In such a situation, an interladder coupling would yield the field-induced long-range incommensurate order. Several phase diagrams including the magnetization plateau are also presented.