Badih Assaf: Magnetooptical Infrared Spectroscopy of Magnetic Topological Materials

Speaker:

Badih Assaf

University of Notre Dame

Abstract:

Magnetic topological materials have primarily been studied to realize the quantization of the Hall effect at zero magnetic field which was discovered in 2013 [1]. The optical properties of these materials remain, however, nearly unharnessed. The gapless nature of topological states, combined with magnetic exchange opens interesting avenues for the development of polarization sensitive sensing devices, at long wavelengths. In this context, my talk will discuss our recent magnetooptical infrared spectroscopy measurements on two types of topological insulators subjected to magnetism through the proximity effect and intrinsically. First, I will discuss our observation of a strong infrared magnetic circular dichroism in the optical absorption of the intrinsic magnetic topological insulator MnBi2Te4 under applied magnetic field. The dichroism reaches 1.8% at 30T for a 40nm film, survives down to 5T and likely originates from the splitting of the valence and conduction bands in the presence of a finite out-of-plane magnetization [2]. Second, I will present our scheme to artificially introduce magnetic exchange [3] into the high mobility topological material Pb1-xSnxSe to realize a polarization sensitive response from surface states down to the far-infrared. The results that I will show motivate a deeper investigation of the infrared response of topological materials, which I argue can be relevant for sensing devices.

[1] Chang et al. Science 340 6129 (2013). [2] Bac et al. Npj Quantum Materials 7 46 (2022). [3] Wang et al. arxiv2207.07685