Thursday Mar. 23 at 2:00-3:00 PM, Dreese Lab 260

Title: Molecular Beam Epitaxy for Spintronics: Metals, Semiconductors, and 2D Materials

Abstract: 

Molecular beam epitaxy has played an important role in spintronics for many years. I will give some overview from my own work in metallic multilayers, dilute magnetic semiconductors, and most recently, van der Waals magnets. Then focus on our latest advances in the epitaxial growth of 2D van der Waals (vdW) magnets and their integration with topological insulators (TI). This work is motivated by the realization of topological phases such as the quantum anomalous Hall effect and highly efficient spin-orbit torque produced by TIs. Our initial studies of MnSe₂ growth on Bi₂Se₃ showed a tendency for the interdiffusion of Mn into the Bi₂Se₃. This ultimately led to the synthesis of MnBi₂Se₄ (MBS), a new magnetic TI. Interestingly, the vdW phase is not the thermodynamically stable phase and bulk crystals do not exist, so the epitaxial stabilization of MBS creates the opportunity to explore the magnetic and topological properties of this material. We find that MBS is a layered antiferromagnet, similar to MnBi₂Te₄, but a difference is that the magnetic moments lie in the plane of the film. Angle resolved photoemission experiments show the presence of a topological surface state with Dirac dispersion. For bilayers of 2D magnets and TIs, we have developed FGT films on Bi₂Te₃. We first optimized FGT by studying its growth on Ge(111) substrates, where we find that kinetic considerations play a major role. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT films to have atomically smooth surfaces and abrupt interfaces with the Ge(111). Subsequently, we have developed the growth of FGT on Bi₂Te₃ for the integration of 2D magnets with TIs. Interestingly, we observe room temperature ferromagnetism in FGT/Bi₂Te₃ heterostructures by varying the growth conditions.

Bio:

Roland Kawakami is a Professor in the Department of Physics at the Ohio State University. He was previously a Professor in the Department of Physics and Astronomy at the University of California, Riverside. He received his Ph.D. in Physics in 1999 from the University of California, Berkeley and was a postdoctoral researcher at the University of California, Santa Barbara. He joined the University of California, Riverside as a tenure track faculty member in 2002 before moving to Ohio State in 2013. His group is involved in the studies of quantum materials focusing on magnetic and topological phenomena, and studies of 2D materials for electronic charge and spin transport.

Zoom link (if you can only join remotely): https://osu.zoom.us/j/96171324710?pwd=UDVuOXd4cno5cFlYb0w0OEVlbEF3QT09