Magnon condensation in dimerized antiferromagnets with spin-orbit coupling

Bose-Einstein condensation (BEC) of triplet excitations triggered by a magnetic field, sometimes called magnon BEC, in dimerized antiferromagnets gives rise to a long-range antiferromagnetic order in the plane perpendicular to the applied magnetic field. To explore the effects of spin-orbit coupling on magnon condensation, we study a spin model on a distorted honeycomb lattice with dimerized Heisenberg exchange (J terms) and uniform off-diagonal exchange (Gamma' terms) interactions. Via variational Monte Carlo calculations and spin-wave theory, we find that an out-of-plane magnetic field can induce different types of long-range magnetic orders, no matter if the ground state is a nonmagnetic dimerized state or an ordered Neel state. Furthermore, the critical properties of field-driven phase transitions in the presence of spin-orbit couplings, as illustrated from the spin-wave spectrum and interpreted by the effective field theory, can be different from the conventional magnon BEC. Our study is helpful to understand the rich phases of spin-orbit coupled antiferromagnets induced by magnetic fields.