Project summary:
Ultrashort laser pulses induced magnetization dynamics, involving the interplay of photons, electrons, spin, orbitals, and lattice dynamics, represent the fastest means to control magnetism and quantum properties of materials on femtosecond and sub-femtosecond time scale. Therefore, this topic became not only relevant for important fundamental problem, but also for technologies applications such as future ultrafast magnetic data storage and spintronics. However, a complete understanding of the underlying physical process of light-induced spin dynamics is still hard to reach. On the other hand, the discovery of two-dimensional (2D) van der Waals (vdW) magnetic crystals (e.g., CrI₃ and Fe₃GeTe₂) provides an ideal testbed for manipulating the magnetic properties and exploring new physical phenomena at the atomically thin and 2D limit. Recent breakthroughs on controlling magnetism and interfacial spin transfer with light have been reported in 2D materials and vdW heterostructures. (Nat. Mater., 2022, 21, 1373–1378; PRL, 2020, 125, 267205). Such manipulation on magnetism in the 2D systems will enable continuously controlling the quantum properties, such as valley polarization, by tunable interfacial magnetic proximity. (Nano Lett., 2018, 18, 3823– 3828). Our theoretical works (Nano Lett. 2021, 21, 3237) have shown that the ultrashort laser pulses can induce the interlayer spin transfer and OISTR mechanism on extremely fast (~10 fs) time scales by using real-time time-dependent density functional theory (rt-TDDFT), which has been previous confirmed in the experiment. (Nature, 2019, 571, 240-244). Despite these theoretical and experimental works, the basic mechanism for light induced spin dynamic process in 2D systems remain relatively unexplored. Particularly, the spin-orbital-lattice angular momentum transfer mechanism and the role of phonon during spin dynamics process remain rather elusive. 

The project will aim to answer and disentangle three important fundamental problems based on the ab initio quantum dynamics study: (i) Exploring the dynamics of spin and orbitals momentum after photoexcitation in 2D limit, (ii) Understanding the the role of phonon mode during spin dynamics, and (iii) Exploring the angular moment transfer driven by optical helicity. 

Methods to be used in the project contain the density functional theory (DFT), real-time time-dependent DFT (rt-TDDFT), ab initio Ehrenfest dynamics, atomistic spin model, and lattice dynamics.

Requirements:

• Applicant should hold a master’s degree in physics, chemistry, or materials Science with a strong background in solid state physics or the first-principles computational methods. 
• Experience with time dependent DFT and atomistic spin model will be considered as benefits.
• Demonstrated ability to work independently and as part of a team.
• Demonstrated ability to write research reports or other publications to a publishable standard

Publications of the research group relevant to the topic:

1. J. He, S. Li, A. Bandyopadhyay, T. Frauenheim, Unravelling Photoinduced Interlayer Spin Transfer Dynamics in 2D Nonmagnetic-Ferromagnetic van der Waals Heterostructures, Nano Lett., 2021, 21, 3237-3244.
2. J. He, S. Li, L. Zhou, T. Frauenheim, Ultrafast Light-Induced Ferromagnetic State in Transition Metal Dichalcogenides Monolayers. J. Phys. Chem. Lett., 2022, 13, 2765-2771.
3. Z. Zhou, J. He, T. Frauenheim, O. V. Prezhdo, J. Wang, Control of Hot Carrier Cooling in Lead Halide Perovskites by Point Defects. J. Am. Chem. Soc., 2022, 144, 18126–18134.
4. S. Li, L. Zhou, T. Frauenheim, J. He, Light-Controlled Ultrafast Magnetic State Transition in Antiferromagnetic -ferromagnetic van der Waals Heterostructures. J. Phys. Chem. Lett., 2022, 13, 6223-6229.
5. J. He, T. Frauenheim, Optically driven ultrafast magnetic order transitions in two-dimensional ferrimagnetic MXenes. J. Phys. Chem. Lett., 2020, 11, 15, 6219–6226.