Dynamical DMRG study of spin excitation dynamics in triangular lattice spin-1/2 antiferromagnet

Recently, the theoretical understanding of the ground state of frustrated two-dimensional spin-1/2 antiferromagnetic Heisenberg models has been dramatically progressed. In contrast, much less has been understood for the spin excitation dynamics. For example, it is well established by now that 120 degree Néel order appears in the ground state of the triangular lattice spin-1/2 antiferromagnetic Heisenberg model. However, the spin excitation dynamics is still under active debate. In fact, the spin excitations observed by recent neutron scattering for Ba₃CoSb₂O₉, modeled by the triangular lattice spin-1/2 antiferromagnetic Heisenberg model, cannot be explained by the linear spin wave theory. By using the dynamical DMRG method, here we investigate the spin excitation dynamics of the triangular lattice spin-1/2 antiferromagnetic Heisenberg model. We find that our results are in good agreement with the experimental results for Ba₃CoSb₂O₉, implying that the quantum fluctuations beyond the linear spin wave theory play an important role on the spin excitations dynamics of Ba₃CoSb₂O₉.