Optical control of competing exchange interactions and coherent spin-charge coupling in two-orbital Mott insulators

Abstract

In order to have a better understanding of ultrafast electrical control of exchange interactions in multi-orbital systems, we study a two-orbital Hubbard model at half filling under the action of a time-periodic electric field. Using suitable projection operators and a generalized time-dependent canonical transformation, we derive an effective Hamiltonian which describes two different regimes. First, for a wide range of non-resonant frequencies, we find a change of the bilinear Heisenberg exchange J ex that is analogous to the single-orbital case. Moreover we demonstrate that also the additional biquadratic exchange interaction B ex can be enhanced, reduced and even change sign depending on the electric field. Second, for special driving frequencies, we demonstrate a novel spin-charge coupling phenomenon enabling coherent transfer between spin and charge degrees of freedom of doubly ionized states. These results are confirmed by an exact time-evolution of the full two-orbital Mott-Hubbard Hamiltonian. Contents arXiv:1803.03796v2 [cond-mat.str-el] 1 Feb 2019 SciPost Physics Submission A Projection operators 19 B Effective Hamiltonian 20 C Spin-one and pseudo spin-one operators 22 D Derivation of the effective spin-one Hamiltonian 23 E Effective Hamiltonian with Spin-Charge coupling 27 References 28

Biquadratic exchange interactions in two-dimensional magnets

“…As our results indicate that BQ exchanges are important for 2D magnets, possible ordered and disordered magnetic regimes may be stabilized in appreciable temperatures. Moreover, it is possible to enhance or suppress BQ interactions in Mott-Hubbard systems by applying external electric fields 53,54 . Indeed, the control of the magnetic properties of CrI 3 using electrical means has already been demonstrated 31 .…”

Light-induced topological magnons in two-dimensional van der Waals magnets

“…Although the above model provides a simplified description of realistic monolayer vdW magnets, neglecting both the multi-orbital structure of the transition metals ions and the superexchange processes induced by interactions with the surrounding halides [34,35], it provides a starting point for more advanced treatments. Further, since the topological properties of honeycomb ferromagnets are determined by the lattice structure and the presence or absence of time-reversal symmetry [26], we expect the model to give a correct description of the topological features of the magnon excitations.…”

Higher-order exchange interactions in two-dimensional magnets

“…As our results indicate that BQ exchanges are important for 2D magnets, possible ordered and disordered magnetic regimes may be stabilized in appreciable temperatures. Moreover, it is possible to enhance or suppress BQ interactions in Mott-Hubbard systems by applying external electric fields 46 .…”