title: Ultrafast generation of pseudo-magnetic field for valley excitons in WSe₂ monolayers.
abstract: The valley pseudospin is a degree of freedom that emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2). The capability to manipulate it, in analogy to the control of spin in spintronics, can open up exciting opportunities. Here, we demonstrate that an ultrafast and ultrahigh valley pseudo-magnetic field can be generated by using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Using ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the nonresonant pump, resulting in an energy splitting of more than 10 milli-electron volts between the K and K' valley exciton transitions. Our study opens up the possibility to coherently manipulate the valley polarization for quantum information applications.
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.
authors.forename: Jonghwan
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Hong
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA.
authors.forename: Chenhao
authors.initials: C
authors.lastname: Jin
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA. Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
authors.forename: Su-Fei
authors.initials: SF
authors.lastname: Shi
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Chih-Yuan S
authors.initials: CY
authors.lastname: Chang
authors.affiliation: Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Chiu
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan. Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
authors.forename: Lain-Jong
authors.initials: LJ
authors.lastname: Li
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA. Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. Kavli Energy NanoSciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. fengwang76@berkeley.edu.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang