Optical manipulation of valley coherence via Landau level transitions in black phosphorus and WTe2 monolayers

TL;DR

This paper theoretically explores how Landau level transitions in black phosphorus and WTe2 monolayers can be used to manipulate valley coherence, revealing enhanced interference effects due to anisotropic properties and distinct spectral profiles.

Contribution

It demonstrates the control of valley quantum interference via inter-Landau level transitions in anisotropic 2D materials, highlighting the role of directional electron transition probabilities.

Findings

Valley quantum interference is over 20 times stronger in Landau-quantized regimes.

Distinct spectral profiles arise from different transition selection rules.

Normalized interference intensities follow exponential functions of magnetic field and Landau level index.

Abstract

Valley coherence is of great significance for exploring fundamental quantum phenomena and developing next-generation valleytronic devices. Herein, we theoretically investigate the valley quantum interference engineered by inter-Landau level (LL) transitions in black phosphorus (BP) and WTe2 monolayers. In contrast to the non-Landau-quantized regime, valley quantum interference is enhanced by over 20-fold, or even significantly stronger, in virtue of striking anisotropic environment. Such anisotropy originates from the distinct electron transition probabilities along the armchair and zigzag directions of BP and WTe2 monolayers. Especially, BP is capable of more effectively strengthening the valley quantum interference response due to its greater directional disparity in electron transition probabilities. The interference fringes also present distinct spectral profiles (e.g., different dip and peak numbers in one interference period) owing to different transition selection rules in BP and WTe2 monolayers. In spite of these discrepancies, normalized interference intensities follow two exponential functions of magnetic field and Landau level index for all the transitions {\delta}n = n'- n = -4, -2, 0, +2, +4 (where n and n' indicate the LL indexes of valence and conduction bands, respectively), and the interference spectra exhibit C2 rotational symmetry about the crystallographic azimuthal angle of 90{\deg}.