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New Pathway to Valleytronics

Pump-induced change of probe beam reflectivity. Illustrates optical Stark shifts of exciton transitions induced by pump pulses.

Scientific Achievement
Demonstrated that a well-established phenomenon known as the ‘optical Stark effect’ can be used to selectively control photoexcited electron/hole pairs (excitons) in different energy valleys as electrons move, wavelike, through a 2D semiconductor.

Significance and Impact
Understanding how to control excitons in different energy valleys opens the possibility of ultrafast manipulation for quantum information applications, with information coded based on electrons’ wavelike movement.

Research Details

  • In valleytronics, electrons move through a 2D semiconductor as a wave with two energy valleys, each characterized by a quantum valley number that encodes information
  • Scientists generated ultrafast and ultrahigh pseudomagnetic fields using circularly polarized femtosecond light pulses to selectively control the valley degree of freedom
  • Ultrafast pump-probe spectroscopy was used to observe a pure and valley-selective optical Stark effect
  • The optical Stark effect describes an energy shift in a two-level system induced by a non-resonant laser field

J Kim, X Hong, C Hin, S Shi, C-Y Chang, M-H Chiu, L-J Li, and F Wang, Science. 2015, 346(6214)