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Carrier Dynamics and Spin-Valley-Layer Effects in Bilayer Transition Metal Dichalcogenides


Transition metal dichalcogenides are an interesting class of low dimensional materials in mono- and few-layer form with diverse applications in valleytronic, optoelectronic and quantum devices. Therefore, the general nature of the band-edges and the interplay with valley dynamics is important from a fundamental and technological standpoint. Bilayers introduce interlayer coupling effects which can have a significant impact on the valley polarization. The combined effect of spin-orbit and interlayer coupling can strongly modify the band structure, phonon interactions and overall carrier dynamics in the material. Here we use first-principles calculations of electron-electron and electron-phonon interactions to investigate bilayer MoS$_2$ and WSe$_2$ in both the $AA'$ and $AB$ stacking configurations. We find that in addition to spin-orbit coupling, interlayer interactions present in the two configurations significantly alter the near-band-edge dynamics. Scattering lifetimes and dynamic behavior is highly material-dependent, despite the similarities and typical trends in TMDCs. Additionally, we capture significant differences in dynamics for the $AA'$ and $AB$ stacking configurations, with lifetime values differing by up to an order of magnitude between them for MoS$_2$. Further, we evaluate the valley polarization times and find that maximum lifetimes at room temperature are on the scale of 1 picosecond for WSe$_2$ in the $AB$ orientation. These results present a pathway to understanding complex heterostructure configurations and `magic angle' physics in TMDCs.

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Publication details

The article was received on 26 Oct 2018, accepted on 26 Nov 2018 and first published on 26 Nov 2018

Article type: Paper
DOI: 10.1039/C8FD00159F
Citation: Faraday Discuss., 2018, Accepted Manuscript
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    Carrier Dynamics and Spin-Valley-Layer Effects in Bilayer Transition Metal Dichalcogenides

    C. J. Ciccarino, C. Chakraborty, D. Englund and P. Narang, Faraday Discuss., 2018, Accepted Manuscript , DOI: 10.1039/C8FD00159F

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