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First published in ACS Nano, v19 i11 published by American Chemical Society. DOI: https://doi.org/10.1021/acsnano.4c18906

Document Type

Article

Publication Version

Published Version

Keywords

2D transition metal dichalcogenide, circularly polarized phonon, helicity-resolved magneto-Raman spectroscopy, MoS2, orbital-phonon coupling, phonon magnetic moment, spin fluctuation

Journal/Book/Conference Title

ACS Nano

Volume

19

Issue

11

First Page

11241

Last Page

11248

Abstract

Recent helicity-resolved magneto-Raman spectroscopy measurement demonstrates large effective phonon magnetic moments of ∼2.5 μB in monolayer MoS2, highlighting resonant excitation of bright excitons as a feasible route to activate Γ-point circularly polarized phonons in transition metal dichalcogenides. However, a microscopic picture of this intriguing phenomenon remains lacking. In this work, we show that an orbital transition between the split conduction bands (Δ0 = 4 meV) of MoS2 couples to the doubly degenerate E″ phonon mode (Ω0 = 33 meV), forming two hybridized states. Our phononic and electronic Raman scattering measurements capture these two states: (i) one with predominantly phonon contribution in the helicity-switched channels and (ii) one with primarily orbital contribution in the helicity-conserved channels. An orbital-phonon coupling model successfully reproduces the large effective magnetic moments of the circularly polarized phonons and explains their thermodynamic properties. Strikingly, the Raman mode from the orbital transition is superimposed on a strong quasi-elastic scattering background, indicating the presence of spin fluctuations. As a result, the electrons excited to the conduction bands through the exciton exhibit paramagnetic behavior although MoS2 is generally considered as a nonmagnetic material. By depositing nanometer-thickness nickel thin films on monolayer MoS2, we tune the electronic structure so that the A exciton perfectly overlaps with the 633 nm laser. The optimization of resonance excitation leads to pronounced tunability of the orbital-phonon hybridized states. Our results generalize the orbital-phonon coupling model of effective phonon magnetic moments to material systems beyond the paramagnets and magnets.

Department

Department of Physics

Original Publication Date

3-13-2025

Object Description

1 PDF File

DOI of published version

10.1021/acsnano.4c18906

Repository

UNI ScholarWorks, Rod Library, University of Northern Iowa

Copyright

©2025 The Author(s)

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Language

en

File Format

application/pdf

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