Ultrafast excitation of coherent spin waves in 2D antiferromagnets

Ultrafast excitation of coherent spin waves in 2D antiferromagnets

Xiaoxiao Zhang
Department of Physics
Cornell University

The recently discovered atomically-thin magnetic crystals provide a unique playground to develop new approaches to manipulate magnetism. On one hand, their van de Waals nature allows easy assemble of complex heterostructures to incorporate strong interfacial interactions. On the other hand, strong electric field and large doping can be conveniently applied in monolayer/few layers of magnetic semiconductors (e.g. CrI3, CrBr3 and Cr2Ge2Te6) with their atomic thickness. Rapid progresses have been made that demonstrate the potentials of utilizing 2D magnets to construct novel spintronics devices. However, their spin dynamics, which are crucial for microscopic understanding and determine the fundamental limit of spin manipulation, still remain elusive due to the difficulty to characterize these micron-sized samples with conventional microwave techniques. In this talk, I will show how we can access and probe the collective spin-wave excitations in an antiferromagnetic bilayer CrI3 with ultrafast pump-probe spectroscopy. Coherent oscillations are observed in the time-resolved spectra of magnetization, and are attributed to the magnon modes of antiferromagnetic resonance in bilayer CrI3. Both the transverse and longitudinal magnon branches are identified, allowing us to extract magnetic anisotropy and exchange energies in these atomically-thin magnetic materials. In the end, I will demonstrate the great gate tunability of magnon frequencies, which is unique for the 2D magnetic system, and reveal the potential to control magnon landscape with flexible electronic devices.