“Phonon-driven spin-Floquet valleytro-magnetism”

Prof. Noejung Park (UNIST)

Aug. 16 (Wed.), 4 PM 

#1322 (E6-2. 1st fl.)

The family of two-dimensional (2D) materials equipped with strong spin-orbit coupling (SOC) display novel properties originating from the broken time- or inversion symmetry, and their spin-valley structures can be adopted as an encoding mechanism for binary information. Here, by performing ab initio real-time time dependent density functional simulation on MoS2, the prototypical 2D material, we show that the spin is not only locked to the valley-momenta but strongly coupled to the optical phonon that lifts the mirror symmetry. This dynamical spin state can be resolved into discrete Floquet-phononic spectra, featured by pairs of Larmor precessions. Once the phonon is pumped so as to break time-reversal symmetry, the resulting spin-Floquet structures induce net out-of-plane magnetizations in the otherwise non-magnetic 2D material. This phonon-dressed spin state is an intrinsic excitation of SOC systems that can be controlled by infrared coherent laser excitation, which opens a new avenue toward dynamical spin manipulation.

Contact: MyungJoon Han, Physics Dept., (mj.han@kaist.ac.kr)