Faraday and Kerr effects on 2D optical resonances: layered semiconductors vs quantum wells

Magneto-optical spectroscopy on 2D materials is traditionally performed by magneto-photoluminescence and magneto-reflectance spectroscopy methods. These techniques provide vital information on various aspects of 2D semiconductors and magnets such as spin-valley-layer-resolved band structure, circularly-polarized excitons and trions, magneto-valley polarization, valley coherence, and single-photon emission [1]. However, one normally needs large magnetic fields such as B > 5 T for a reasonable signal-to-noise ratio. For measurements under low magnetic fields (B < 1 T), differential magneto-optical spectroscopy such as Faraday and Kerr effect spectroscopy is highly desirable. In this talk, I will discuss our recent developments on establishing some of these techniques (Faraday rotation [2,3] and spectroscopic ellipsometry). We overcome the bottleneck of long measurement times in these methods, and enhance the speed of data acquisition by two-to-three orders of magnitude using our innovations [3]. I will describe our first results of Zeeman spectroscopy of intra- and interlayer excitons, and trions in 2D materials such as MoS₂, MoSe₂, WS₂ and WSe₂ using Faraday rotation spectroscopy [3]. For the first time, we are able to extract the complete dielectric tensor of these 2D materials [2]. Furthermore, I will discuss our recent discovery of the excited state of a bound 3 particle complex (a trion) in a GaAs quantum well using Kerr spectroscopy under moderately large magnetic fields up to 6 T [4]. Here we solve a four-decades old problem on the existence of excited trions in a quantum well. Our works open new paradigms to explore new spin-valley physics in 2D semiconductors and magnets using sensitive magneto-optical spectroscopy.

References:

1. Check reviews at: a) A. Arora, J. Appl. Phys. 129, 120902 (2021) and b) Glazov et al., MRS Bulletin 49, 899(2024)
2. Carey et al., Nature Communications 15 (1), 3082 (2024)
3. Carey et al, Small Methods 101 (6), 2200885 (2022)
4. Jain et al., submitted (2025)