Physics Colloquium | Spins in 2D Materials, Oct. 16

Roland Kawakami

The Physics & Astronomy Colloquium Series presents Dr. Roland Kawakami of the Ohio State University on “Spins in 2D Materials” on Friday, Oct. 16, at 4:10 p.m. in Walter 245.

Abstract: Two-dimensional crystals such as graphene and monolayer transition metal dichalcogenides (TMD) possess unique properties not found in bulk materials. These materials are atomically-thin, yet are strong enough to remain intact as free standing membranes. Because these materials are “all surface”, they tend to be highly surface sensitive and amenable to inducing proximity effects.

In this talk, I will discuss our progress of investigating spin-dependent phenomena in graphene and TMD monolayers. We investigate spin transport in graphene utilizing ferromagnetic electrodes to inject and detect spin polarized conduction electrons. Spin transport is observed up to room temperature with spin diffusion lengths of a few microns, making it a promising material for spintronics. One of the outstanding issues in the field involves the generation of magnetic moments and magnetic ordering originating from point defects (i.e. vacancies, hydrogen adatoms, etc.). We utilize spin transport as an ultrasensitive magnetometer to probe the magnetic properties of point defects in graphene and provide clear evidence for defect-induced magnetic moments.

Recently, we have turned our attention to spin dynamics in monolayer TMD, which is expected to have unusual properties due to the presence of Berry curvature and strong spin-orbit coupling. To this end, we have implemented time-resolved Kerr rotation microscopy to measure the spin dynamics in WS₂ with spatial resolution better than 1 micron and temporal resolution of 150 fs. While most previous studies using large spots have shown short spin/valley lifetimes of tens of picoseconds, our results show spin lifetimes in excess of 4 ns at particular locations on the sample. We will discuss the spatial variation of the spin lifetime as well as its correlation with the photoluminescence properties.