Two-dimensional (2D) atomic crystals, such as graphene and transition-metal dichalcogenides, have emerged as a new class of materials with remarkable physical properties. In contrast to graphene, monolayer MoS 2 is a non-centrosymmetric material with a direct energy gap. Strong photoluminescence, a current on/off ratio exceeding 10 8 in field-effect transistors, and efficient valley and spin control by optical helicity have recently been demonstrated in this material. Here we report the spectroscopic identification in a monolayer MoS 2 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.
Bibliographical noteFunding Information:
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.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering