Quasiparticle energies and excitonic effects of chromium trichloride

Recently fabricated two-dimensional (2D) van der Waals (vdW) magnetic structures provide precious opportunities to study many-electron interactions and excited state properties of correlated materials under quantum confinement. Employing first-principles many-body perturbation simulations, we reveal enhanced excitonic effects in 2D and bulk forms of magnetic CrCl3. Unlike usual nonmagnetic vdW semiconductors, in which excited state properties are sensitive to dimensionality, many-electron interactions dominate quasiparticle energies and optical responses of both two-dimensional and bulk CrCl3. The calculated electron-hole (e-h) binding energy can reach 3 eV in monolayer and remains as high as 2 eV in bulk. Particularly, the two-particle e-h binding energy is more sensitive to the quantum confinement than the single-particle self-energy correction. As a result, an unusual red shift of the "optical gap" is observed in thinner samples, which is opposite to the widely observed blue shift trend in nanostructures. The unusual quantum confinement effect in CrCl3 extends our understanding of many-electron interactions in the vdW magnets.

1. L. Zhu, L. Yang, Phys. Rev. B 101, 245401 (2020).