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arXiv:2112.04690 · Physical review. B./Physical review. B

Polarization-dependent magnetic properties of periodically driven α−RuCl3

Naoya Arakawa, Kenji Yonemitsu

Published Dec 8, 2021• 6 citations
arXivHTMLPDF

Abstract

We study magnetic properties of a periodically driven Mott insulator with strong spin-orbit coupling and show some properties characteristic of linearly polarized light. We consider a ${t}_{2g}$-orbital Hubbard model driven by circularly or linearly polarized light with strong spin-orbit coupling and derive its effective Hamiltonian in the strong-interaction limit for a high-frequency case. We show that linearly polarized light can change not only the magnitudes and signs of the exchange interactions, but also their bond anisotropy even without the bond-anisotropic hopping integrals. Because of this property, the honeycomb-network spin system could be transformed into weakly coupled zigzag or step spin chains for the light field polarized along the $b$ or $a$ axis, respectively. Then, analyzing how the light fields affect several magnetic states in a mean-field approximation, we show that linearly polarized light can change the relative stability of the competing magnetic states, whereas such a change is absent for circularly polarized light. We also analyze the effects of both the bond anisotropy of nearest-neighbor hopping integrals and a third-neighbor hopping integral on the magnetic states and show that the results obtained in a simple model, in which the bond-averaged nearest-neighbor hopping integrals are considered, remain qualitatively unchanged except for the stability of zigzag states in the nondriven case and the degeneracy lifting of the zigzag or stripy states.

DOI
10.1103/physrevb.104.214413

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We study magnetic properties of a periodically driven Mott insulator with strong spin-orbit coupling and show some properties characteristic of linearly polarized light. We consider a t2g{t}_{2g}t2g​-orbital Hubbard model driven by circularly or linearly polarized light with strong spin-orbit coupling and derive its effective Hamiltonian in the strong-interaction limit for a high-frequency case. We show that linearly polarized light can change not only the magnitudes and signs of the exchange interactions, but also their bond anisotropy even without the bond-anisotropic hopping integrals. Because of this property, the honeycomb-network spin system could be transformed into weakly coupled zigzag or step spin chains for the light field polarized along the bbb or aaa axis, respectively. Then, analyzing how the light fields affect several magnetic states in a mean-field approximation, we show that linearly polarized light can change the relative stability of the competing magnetic states, whereas such a change is absent for circularly polarized light. We also analyze the effects of both the bond anisotropy of nearest-neighbor hopping integrals and a third-neighbor hopping integral on the magnetic states and show that the results obtained in a simple model, in which the bond-averaged nearest-neighbor hopping integrals are considered, remain qualitatively unchanged except for the stability of zigzag states in the nondriven case and the degeneracy lifting of the zigzag or stripy states.
We study the effective spin-orbital model for honeycomb-layered transition metal compounds, applying the second-order perturbation theory to the three-orbital Hubbard model with the anisotropic hoppings. This model is reduced to the Kitaev model in the strong spin-orbit coupling limit. Combining the cluster mean-field approximations with the exact diagonalization, we treat the Kugel-Khomskii type superexchange interaction and spin-orbit coupling on an equal footing to discuss ground-state properties. We find that a zigzag ordered state is realized in the model within nearest-neighbor interactions. We clarify how the ordered state competes with the nonmagnetic state, which is adiabatically connected to the quantum spin liquid state realized in a strong spin-orbit coupling limit. Thermodynamic properties are also addressed. The present paper should provide another route to account for the Kitaev-based magnetic properties in candidate materials.
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Hidden multipolar orders in spin-orbit-coupled Mott insulators provide a promising setting for correlated quantum matter, yet their control and detection remain major challenges. Here, we demonstrate that circularly polarized light enables both the control and detection of hidden multipolar order in 4d2/5d24d^2/5d^24d2/5d2 systems with edge-sharing octahedra. Using a Floquet Schrieffer-Wolff expansion of a driven Hubbard-Kanamori model, we derive a low-energy multipolar Hamiltonian with two qualitatively new light-driven terms. One is an effective static field that couples linearly to the magnetic octupole, realizing an octupolar inverse Faraday effect. The other is a bond-dependent anisotropic exchange interaction absent in equilibrium. These two couplings constitute the key mechanisms of this work: the first provides a direct optical handle on hidden octupolar order, while the second reorganizes the multipolar exchange landscape and introduces strong bond-dependent frustration. Together, these couplings define a nonequilibrium multipolar Hamiltonian whose phase diagram contains robust antiferro-octupolar, ferro-octupolar, and partially polarized ferro-quadrupolar phases, alongside a putative Ising-octupolar regime and a strongly frustrated, liquid-like multipolar regime whose finite-size numerical signatures are compatible with Kitaev-type behavior. We further show that the induced multipolar order couples to the lattice, generating reversible trigonal and orthorhombic or tetragonal distortions that provide symmetry-resolved structural fingerprints in pump-probe experiments. In this way, our work establishes a general mechanism for the optical generation, control, and detection of hidden multipolar quantum states.
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Scalar spin chirality, a three-body spin correlation that breaks time-reversal symmetry, is revealed to couple directly to circularly polarized laser. This is shown by the Floquet formalism for the periodically driven repulsive Hubbard model with a strong-coupling expansion. A systematic derivation of the effective low-energy Hamiltonian for a spin degree of freedom reveals that the coupling constant for scalar spin chirality can become significant for a situation in which the driving frequency and the on-site interaction are comparable. This implies that the scalar chirality can be induced by circularly polarized lights, or that it can be used conversely for probing the chirality in Mott insulators as a circular dichroism.