Quantitatively predicting angle-resolved polarized Raman intensity of anisotropic layered materials

TL;DR

This paper develops a quantitative framework to predict angle-resolved polarized Raman intensities in anisotropic layered materials, accounting for multilayer interference, birefringence, and dichroism, aiding understanding of their optical anisotropy.

Contribution

It introduces intrinsic Raman tensors and effective Raman tensors to accurately predict ARPR responses in thick and thin anisotropic layered materials, considering complex refractive indexes and multilayer effects.

Findings

Successfully predicts ARPR intensity profiles for black phosphorus and Td-WTe2.

Demonstrates dependence of ARPR on thickness, substrate, and wavelength.

Framework applicable to various anisotropic layered materials.

Abstract

Angle-resolved polarized Raman (ARPR) spectroscopy provides insights into optical anisotropy and symmetry-related electron-photon/electron-phonon couplings of anisotropic layered materials (ALMs). However, since their discovery over ten years ago, ARPR responses in ALM flakes has exhibited a puzzling dependence on flake thickness, excitation wavelength, and dielectric environment, complicating their understanding and prediction. By taking black phosphorus (BP) (large than 20 nm) flakes and four-layer Td-WTe2 as examples, this study introduces intrinsic Raman tensors (Rint) and proposes strategies to predict the ARPR intensity profiles of thick and atomically-thin ALM flakes by considering birefringence, linear dichroism and multilayer interference inside multilayered structures with experimentally determined complex refractive indexes along in-plane axes and complex tensor elements of Rint for the corresponding phonon modes. The tensor elements of effective Raman tensors (Reff), which are directly linked to the polarization vectors of incident and scattered light outside the ALM surface, were derived to quantitatively predict ARPR intensity for these ALM flakes, showing intricate dependence on ALM thickness, dielectric substrates, and excitation wavelengths. This framework can be extended to other ALM flakes from atomically-thin layers to bulk limit, facilitating comprehensive prediction of their ARPR intensity regardless of layer-dependent electronic properties.