Photoinduced entanglement in a magnonic Floquet topological insulator

When irradiated via high-frequency circularly polarized light, the stroboscopic dynamics in a Heisenberg spin system on a honeycomb lattice develops a next-nearest-neighbor (NNN) Dzyaloshinskii-Moriya (DM) type term, making it a magnonic Floquet topological insulator. We investigate the entanglement generation and its evolution on such systems, particularly an irradiated ferromagnetic XXZ spin-1/2 model in a honeycomb lattice as the system parameters are optically tuned. In the high-frequency limit, we compute the lowest quasienergy state entanglement in terms of the concurrence between nearest-neighbor (NN) and NNN pair of spins and witness the entanglement transitions occurring there. For the easy-axis scenario, the unirradiated system forms a product state but entanglement grows between the NNN spin pairs beyond some cutoff DM strength. Contrarily in the easy-planar case, NN and NNN spins remain already entangled in the unirradiated limit. It then goes through an entanglement transition which causes decrease (increase) of the NN (NNN) concurrences down to zero (up to some higher value) at some critical finite DM interaction strength. For a high frequency of irradiation and a suitably chosen anisotropy parameter, we can vary the field strength to witness sudden death and revival of entanglement in the Floquet system. Both exact diagonalization and modified Lanczos techniques are used to obtain the results up to 24 site lattice. We also calculate the thermal entanglement and obtain estimates for the threshold temperatures below which nonzero concurrence can be expected in the system.