MELTING OF AN ANTIFERROMAGNETIC HEISENBERG SPIN CHAIN BY EXTERNAL MAGNETIC-FIELDS

We study the magnetic-field-induced insulator-metal transition in the t-J' chain model at quarter filling. In this model the nearest-neighbo ur hopping energy t competes with the next-nearest-neighbour exchange energy J', and for a small t/J' the system is an insulator accompanied by a charge ordering. Response to external magnetic fields is investi gated numerically by the density-matrix renormalization-group method. We have found that a transition from the charge ordered insulating pha se to a metallic phase occurs at a finite strength of the magnetic fie ld for small t/J'. The transition is an example of magnetic-field-indu ced melting transition of a quantum antiferromagnetic Heisenberg spin chain system.