Valley control at the femtoscale

Spin and valley indices represent the key quantum labels of quasiparticles in a wide class of two dimensional materials, and form the foundational elements of the fields of spintronics and valleytronics. Control over these degrees of freedom, the creation of valley and spin states as well as the generation of pure spin and valley currents, remains a central challenge in these fields. Employing both tight-binding and state-of-the-art time dependent density function theory I will show how at femtosecond time scales valley coupling is a much more general effect. We find that two time separated linearly polarized pulses allow almost complete control over valley excitation, with the pulse time difference and polarization vectors emerging as key parameters for valley control [1]. Furthermore, by combining optical frequency circularly polarized pulse and a terahertz frequency linearly polarized pulse, a so-called "hencomb" pulse, can generate precisely tailored and nearly 100% pure valley and spin currents in bilayer graphene and the dichalocogenide WSe2 [2]. Finally I discuss how valley currents can be made in minimally (< 20meV) gapped graphene [3].
[1] S. Sharma, P. Elliott, and S. Shallcross, Optica 9, 947-952 (2022)[2] S. Sharma, P. Elliott, and S. Shallcross, Submitted Sci. Adv.[3] S. Sharma and S. Shallcross, Submitted Optica
Host: Julen Ibanez
Place

Auditorium, Centro de Fisica de Materiales

Who

Samuel Shallcross, Max-Born Institute (Berlin)

Source Name

CFM