Chiral phonons for spin control in semiconductors

• Applicant: Dr. Olga Ken
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 529684269

Circularly polarized (chiral) phonons serve as one of the basic elements in realizing nontrivial quantum mechanical phenomena. The phonon angular momentum emerges in systems where the spatial-inversion or time-reversal symmetry is broken, e.g. chiral materials or ferromagnets. The phonon angular momentum is also emergent at the surface of a semiconductor in a form of the Rayleigh surface acoustic wave (SAW), which has elliptically polarized displacement. Its angular momentum lies in the plane of the surface. The interactions involving chiral phonons are very appealing, because chiral phonons can couple to spins of the charge carriers via spin-phonon (Bir-Pikus) interaction. This project focuses on control of hole spins in the valence band of nonmagnetic GaAs semiconductor via spin-orbit coupling to circularly polarized (chiral) phonons. Two mechanisms of spin-phonon interaction will be investigated, namely the AC phonon Stark effect and phonon orientation of hole spins. The AC phonon Stark effect will be used to selectively modulate the energy of hole spin levels in a AlGaAs/GaAs heterostructure. Phonon orientation will result in redistribution of the hole population on the spin levels due to spin-dependent absorption of resonant phonons. Application of the external magnetic field will allow tuning the Zeeman splitting of the hole spin-levels into and out of the resonance with phonon energy. This will allow us to distinguishing between the two mechanisms under study. Chiral phonons will be generated in the form of Rayleigh surface acoustic wave by pumping a non-magnetic metal grating deposited on top of the AlGaAs/GaAs heterostructure with fs-laser pulses. The detection will be accomplished by optical orientation of the charge carriers, time-resolved photoluminescence and pump-probe Kerr rotation measurements, and Brillioun scattering spectroscopy with micrometer spatial resolution. The obtained results will significantly contribute to development of methods of the phonon polarization spectroscopy that can become a powerful experimental tool in the spin physics of semiconductors.

• DFG Programme: WBP Position