Sebastian Schaper | Searcharxiv

arXiv2026

Dielectric Tensor of CrSBr from Spectroscopic Imaging Ellipsometry

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.

cond-mat.mtrl-sci↗

arXiv2025

Unambiguous determination of optical constants and thickness of ultrathin films by using optical anisotropic substrates

The unambiguous and universal determination of optical constants such as complex refractive indices (n, k) and thickness (d) in one measurement is typically confined for films with a thickness of more than 10~nm that hampers its application for ultra-thin films such as two-dimensional materials. We demonstrate that the commonly accepted limit of n, k, d coupling is overcome in ellipsometry by utilizing anisotropic substrates. In this way, ellipsometry allows to determine n, k and d simultaneously for thicknesses lower than 1~nm with high accuracy. Extensive simulations proof the potential of using anisotropic substrates for decoupling. The simultaneous determination of n, k and d is of great interest in several fields, two-dimensional materials, their heterostructures, ultra thin films for application in quantum technology, plasmonics and nano-photonics.

physics.optics↗