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Tightly bound trions in monolayer MoS2


Two-dimensional (2D) atomic crystals, such as graphene and transition-metal dichalcogenides, have emerged as a new class of materials with remarkable physical properties1. In contrast to graphene, monolayer MoS2 is a non-centrosymmetric material with a direct energy gap2,3,4,5. Strong photoluminescence2,3, a current on/off ratio exceeding 108 in field-effect transistors6, and efficient valley and spin control by optical helicity7,8,9 have recently been demonstrated in this material. Here we report the spectroscopic identification in a monolayer MoS2 field-effect transistor of tightly bound negative trions, a quasiparticle composed of two electrons and a hole. These quasiparticles, which can be optically created with valley and spin polarized holes, have no analogue in conventional semiconductors. They also possess a large binding energy (~ 20 meV), rendering them significant even at room temperature. Our results open up possibilities both for fundamental studies of many-body interactions and for optoelectronic and valleytronic applications in 2D atomic crystals.

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Figure 1: Atomic structure, electronic band structure, and absorption spectrum of monolayer MoS2.
Figure 2: Doping dependence of the optical properties of a monolayer MoS2 FET.
Figure 3: Excitons and trions at room temperature in monolayer MoS2.
Figure 4: Valley and spin control of trions in monolayer MoS2.

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This research was supported by the National Science Foundation through grants DMR-0907477 and the Research Corporation Scialog Program at Case Western Reserve University; and by the National Science Foundation through grants DMR-1106172 and 1122594 and by the Department of Energy, Office of Basic Energy Sciences through grant DE-FG02-07ER15842 at Columbia University and through grant DE-SC0001085 for optical instrumentation at Columbia University’s Center for Re-Defining Photovoltaic Efficiency through Molecule Scale Control. C.L. acknowledges support from the Korean government Ministry of Education grant Global Frontier Research Center for Advanced Soft Electronics (2011-0031629), and G.H.L. support from Samsung-SKKU Graphene Center.

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K.F.M. and J.S. designed the experiment, performed the measurement and analysis, and prepared the manuscript; K.H. fabricated MoS2 FET devices and measured photoluminescence; C.L. and J.H. developed MoS2 FET devices; G.H.L fabricated MoS2 samples on BN; T.F.H. contributed to the interpretation of the results and writing of the manuscript.

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Correspondence to Jie Shan.

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The authors declare no competing financial interests.

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Mak, K., He, K., Lee, C. et al. Tightly bound trions in monolayer MoS2. Nature Mater 12, 207–211 (2013).

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