Measuring valley polarization in two-dimensional materials with second-harmonic spectroscopy
Abstract
A population imbalance at different valleys of an electronic system lowers its effective rotational symmetry. We introduce a technique to measure such imbalance - a valley polarization - that exploits the unique fingerprints of this symmetry reduction in the polarization-dependent second-harmonic generation (SHG). We present the principle and detection scheme in the context of hexagonal two-dimensional crystals, which include graphene-based systems and the family of transition metal dichalcogenides, and provide a direct experimental demonstration using a 2H-MoSe monolayer at room temperature. We deliberately use the simplest possible setup, where a single pulsed laser beam simultaneously controls the valley imbalance and tracks the SHG process. We further developed a model of the transient population dynamics which analytically describes the valley-induced SHG rotation in very good agreement with the experiment. In addition to providing the first experimental demonstration of the effect, this work establishes a conceptually simple, com-pact and transferable way of measuring instantaneous valley polarization, with direct applicability in the nascent field of valleytronics.
Cite
@article{arxiv.1903.01367,
title = {Measuring valley polarization in two-dimensional materials with second-harmonic spectroscopy},
author = {Yi Wei Ho and Henrique Guimarães Rosa and Ivan Verzhbitskiy and Manuel Jose de Lima Ferreira Rodrigues and Takashi Taniguchi and Kenji Watanabe and Goki Eda and Vitor Manuel Pereira and José Carlos Viana Gomes},
journal= {arXiv preprint arXiv:1903.01367},
year = {2020}
}