Magneto-optical response of chromium trihalide monolayers: chemical trends

Abstract

Chromium trihalides (CrI 3 , CrBr 3 and CrCl 3 ) form a prominent family of isostructural insulating layered materials in which ferromagnetic order has been observed down to the monolayer. Here we provide a comprehensive computational study of magnetooptical properties that are used as probes for the monolayer ferromagnetic order: magnetic circular dichroism and magneto-optic Kerr effect. Using a combination of density functional and Bethe-Salpeter theories, we calculate both the optical absorption and the magneto-optical Kerr angle spectra, including both excitonic effects and spinorial wave functions. We compare the magneto-optical response of the chromium trihalides series and we find that its strength is governed by the spin-orbit coupling of the ligand atoms (I, Br, Cl).

Quasiparticle energies and excitonic effects of chromium trichloride: From two dimensions to bulk

“…These bright excitons dominate the main optical absorption spectrum. Our calculated e-h binding energies of monolayer CrCl3 are in agreement with recent theoretical calculations [26].…”

“…In order to better describe the correlated 3d orbitals in chromium atoms in the DFT level ground state calculations, the on-site Hubbard interaction [41] is included with parameters U=1.5 eV and J=0.5 eV, which have been used in previous studies of CrI3 and successfully explained available measurements [25,26]. To avoid the double-counting problem in this DFT+U/MBPT scheme, we have subtracted the DFT-level Hubbard potential 𝑉 𝐻𝑢𝑏 together with the DFT exchangecorrelation potential 𝑉 𝑥𝑐 from the conventional self-energy operator 𝛴(𝐸) within the GW approximation, following Ref.…”

“…Because of enhanced light-matter interactions, layered vdW magnetic structures exhibit significant magneto-optical effects, such as the magneto-optical Faraday and Kerr effects and magnetic circular dichroism (MCD), which have been applied to identify magnetic orders [17,18,22] and give rise to optomagnetic applications based on vdW structures [23,24]. More recently, enhanced excitonic effects on magneto-optical responses have been calculated for monolayer magnetic structures [25,26]. These theoretical works showed that e-h binding energy can be 1.7 eV in monolayer CrI3 [25], which is substantially larger than those of other non-magnetic semiconductors and satisfactorily explained available measurements.…”

Magnetic Two-Dimensional Chromium Trihalides: A Theoretical Perspective

“…First principles calculation show that the strength of the MOKE is governed by the spin orbit coupling of the ligand. 51 These calculations, that include a GW description of the quasiparticles and solve the Bethe-Salpeter equation, also show a very strong excitonic effect in the 3 chromium trihalides, found earlier for CrI 3 . 52…”