Large, valley-exclusive Bloch-Siegert shift in monolayer WS[subscript 2]

• Main Authors: Lui, Chun Hung (Author), Lee, Yi-Hsien (Author), Sie, Edbert Jarvis (Contributor), Kong, Jing (Contributor), Gedik, Nuh (Contributor), Fu, Liang (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science (Contributor), Massachusetts Institute of Technology. Department of Physics (Contributor)
• Format: Article
• Language: English
• Published: American Association for the Advancement of Science (AAAS), 2017-06-05T16:07:12Z.
• Subjects: Article
• Online Access: Get fulltext

Coherent interaction with off-resonance light can be used to shift the energy levels of atoms, molecules, and solids. The dominant effect is the optical Stark shift, but there is an additional contribution from the so-called Bloch-Siegert shift that has eluded direct and exclusive observation in solids. We observed an exceptionally large Bloch-Siegert shift in monolayer tungsten disulfide (WS[subscript 2]) under infrared optical driving. By controlling the light helicity, we could confine the Bloch-Siegert shift to occur only at one valley, and the optical Stark shift at the other valley, because the two effects obey opposite selection rules at different valleys. Such a large and valley-exclusive Bloch-Siegert shift allows for enhanced control over the valleytronic properties of two-dimensional materials.
United States. Department of Energy
United States. Dept. of Energy. Division of Materials Sciences and Engineering
Gordon and Betty Moore Foundation (EPiQS Initiative Grant GBMF4540)
Harvard University. Center for Integrated Quantum Materials (Grant DMR-1231319)