Strongly Correlated Exciton‐Magnetization System for Optical Spin Pumping in CrBr₃ and CrI₃.

Abstract

Ferromagnetism in van der Waals systems, preserved down to a monolayer limit, attracted attention to a class of materials with general composition CrX3 (X=I, Br, and Cl), which are treated now as canonical 2D ferromagnets. Their diverse magnetic properties, such as different easy axes or varying and controllable character of in‐plane or interlayer ferromagnetic coupling, make them promising candidates for spintronic, photonic, optoelectronic, and other applications. Still, significantly different magneto‐optical properties between the three materials have been presenting a challenging puzzle for researchers over the last few years. Herewith, it is demonstrated that despite similar structural and magnetic configurations, the coupling between excitons and magnetization is qualitatively different in CrBr3 and CrI3 films. Through a combination of the optical spin pumping experiments with the state‐of‐the‐art theory describing bound excitonic states in the presence of magnetization, we concluded that the hole‐magnetization coupling has the opposite sign in CrBr3 and CrI3 and also between the ground and excited exciton state. Consequently, efficient spin pumping capabilities are demonstrated in CrBr3 driven by magnetization via spin‐dependent absorption, and the different origins of the magnetic hysteresis in CrBr3 and CrI3 are unraveled.

Hyperbolic exciton polaritons in a van der Waals magnet

“…Simultaneously, the onsite d-d components of the exciton wavefunction are reduced in the ordered AFM phase (Fig. 5f ), leading to a larger oscillator strength 45 , 46 . Together with reduced scattering rates at low temperature, the increased spectral weight from magnetically-induced exciton delocalization allows for robust HEPs in CrSBr.…”

One‐Particle and Excitonic Band Structure in Cubic Boron Arsenide

“…However, the oscillator strengths of the deepest lying dark exciton only get weakly enhanced in presence of SOC. To put it in perspective, in a purely electronic framework, without considering the impact phonons and defects can have on these excitons, the oscillator strength of the 1.5 eV peak remains at least three orders of magnitude lower than the 1.2 eV exciton in CrI [ 22–25 ] and one order lower than the 1.6 eV exciton in NiO [ 26 ] and at least eight orders lower than the exciton in monolayer of MoS 2 . [ 24 ] Interestingly enough, Shin et al [ 1 ] observed a clear photoluminescence peak at 695 nm (1.78 eV) in BAs.…”

Hyperbolic exciton polaritons in a van der Waals magnet

“…Simultaneously, the onsite d-d components of the exciton wavefunction are reduced in the ordered AFM phase (Fig. 5e), leading to a larger oscillator strength (44)(45). Together with reduced scattering rates at low temperature, the increased spectral weight from magnetically-induced exciton delocalization allows for robust HEPs in CrSBr.…”