Dielectric Tensor of CrSBr from Spectroscopic Imaging Ellipsometry

TL;DR

This study uses spectroscopic imaging ellipsometry to measure the dielectric tensor of CrSBr, revealing its optical anisotropy and excitonic features, which are crucial for future spin-optoelectronic applications.

Contribution

First measurement of the full dielectric tensor of CrSBr thin films using spectroscopic imaging ellipsometry, highlighting its anisotropic optical properties and excitonic resonances.

Findings

Identification of three diagonal components of the dielectric tensor.

Observation of two main excitonic bands at 1.3 eV and 1.7 eV.

Polarization of excitons along crystallographic axes.

Abstract

Chromium sulfur bromide (CrSBr) is a magnetic van der Waals semiconductor with a direct bandgap and pronounced anisotropy in its electronic, optical, spin and lattice degrees of freedom. Here, we employ spectroscopic imaging ellipsometry (SIE) and Mueller-matrix analysis to determine the full dielectric tensor of paramagnetic CrSBr thin films. Our measurements reveal optical anisotropy, characterized by three distinct diagonal components of the dielectric tensor. The in-plane elements are dominated by prominent excitonic resonances polarized along the two main crystallographic axes. Two main excitonic bands (A and B excitons) centered around 1.3eV and 1.7eV, respectively, are identified; the A-exciton polarized along the b-crystallographic direction, whereas the B-exciton appears to consist of two nearly degenerate contributions polarized along two orthogonal in-plane crystal axes. These results provide fundamental insight into anisotropic light-matter interactions in CrSBr, relevant for future spin-optoelectronic and photonic applications.