High-Field Phase Transitions in Integrable Quantum Spin Chains

抄録

We study the integrable SU(M) and SU_q(M) quantum spin chains in the high-magnetic-field region at zero temperature. For M=4 we found second-order phase transitions at two different fields, H₁ and H₂. At both transition points, the magnetization curve versus magnetic field has cusps with discontinuities in the magnetic susceptibility. We clarify the mechanism of the phase transitions, from which we conclude that the SU(M) and SU_q(M) quantum spin chains undergo (M-2) times field-induced phase transitions at zero temperature.