Doctoral Thesis: Ultrafast Probing of Nonlinear Dynamics in Quantum Materials: Beyond Linear Response Probes

Emre Ergecen

Abstract:

Van der Waals (vdW) magnets display strong interplay between orbital, lattice and spin degrees of freedom. The strong coupling between different degrees of freedom can hybridize elementary excitations into novel bound states with mixed character and can induce renormalizations in the collective excitation spectra, such as phonons and magnons. In this talk, we first reveal bound states of d-orbitals and phonon modes in two dimensional (2D) antiferromagnetic (AFM) vdW insulator NiPS3.  These states are optically dark above the Néel temperature and become accessible through a local inversion symmetry breaking mechanism induced by magnetism. Our data directly yield electron-phonon coupling strength which exceeds the known highest value in 2D systems by nearly an order of magnitude. Second, using coherent phonon spectroscopy with 20 fs pulses, we observe a strong coupling between the out-of-plane breathing phonon mode and magnetic order in 2D AFM vdW insulator FePS3, which is not visible in Raman spectroscopy. We show that this coupling emerges from the coupling between trigonally split t2g orbitals and magnetic order. Finally, we show that NiI2, a vdW type-II multiferroic, retains its multiferroic properties down to monolayer limit. Our results open new ultrafast pathways to coherent control of magnetic degrees of freedom and collective modes in 2D magnets.

Details

• Date: Monday, April 10
• Time: 3:00 pm - 4:30 pm
• Category: Thesis Defense
• Location: 36-428

Additional Location Details:

Thesis Supervisor: Prof. Nuh Gedik