Ultrafast valley relaxation dynamics in monolayer MoS2 probed by nonequilibrium optical techniques

S. Dal Conte, F. Bottegoni, E. A. A. Pogna, D. De Fazio, S. Ambrogio, I. Bargigia, C. D'Andrea, A. Lombardo, M. Bruna, F. Ciccacci, A. C. Ferrari, G. Cerullo, and M. Finazzi
Phys. Rev. B 92, 235425 – Published 14 December 2015
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  • INTRODUCTION
  • EXPERIMENT
  • RESULTS AND DISCUSSION
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We study the exciton valley relaxation dynamics in single-layer MoS2 by a combination of two nonequilibrium optical techniques: time-resolved Faraday rotation and time-resolved circular dichroism. The depolarization dynamics, measured at 77 K, exhibits a peculiar biexponential decay, characterized by two distinct time scales of 200 fs and 5 ps. The fast relaxation of the valley polarization is in good agreement with a model including the intervalley electron-hole Coulomb exchange as the dominating mechanism. The valley relaxation dynamics is further investigated as a function of temperature and photoinduced exciton density. We measure a strong exciton density dependence of the transient Faraday rotation signal. This indicates the key role of exciton-exciton interactions in MoS2 valley relaxation dynamics.

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    • Received 12 August 2015
    • Revised 3 November 2015

    DOI:https://doi.org/10.1103/PhysRevB.92.235425

    ©2015 American Physical Society

    Authors & Affiliations

    S. Dal Conte1,2, F. Bottegoni2, E. A. A. Pogna2, D. De Fazio3, S. Ambrogio4, I. Bargigia5, C. D'Andrea2,5, A. Lombardo3, M. Bruna3, F. Ciccacci2, A. C. Ferrari3, G. Cerullo1,2, and M. Finazzi2

    • 1IFN-CNR, Piazza L. da Vinci 32, I-20133 Milano, Italy
    • 2Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, I-20133 Milano, Italy
    • 3Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, United Kingdom
    • 4Dipartimento di Elettronica, Informatica e Bioingegneria, Politecnico di Milano and IU.NET, I-20133 Milano, Italy
    • 5Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, via Giovanni Pascoli 70/3, 20133 Milan, Italy

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    Issue

    Vol. 92, Iss. 23 — 15 December 2015

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