|Berend Thomas Jonker
This program addresses spin-dependent carrier properties in group IV materials (graphene, Si, Ge), accessed by transport, optical, or magnetic measurements. The principle objective is to develop a fundamental understanding of magnetoelectric phenomena in group IV nanostructures to enable sensing, information storage, and processing beyond Moore’s law. This effort will develop novel phenomena such as the inverse spin Hall effect to control spin-dependent processes, novel materials such as functionalized graphene for spin transport, and determine spin properties of high mobility Si-Ge two dimensional electron gas heterostructures.
We are interested in determining fundamental properties including spin lifetimes and scattering mechanisms, as well as in demonstrating prototype device concepts such as novel magnetic tunnel junctions (MTJ), spin-LEDs, or spin-RTDs. Our recent work has shown that 2D materials such as graphene can be used as a novel tunnel barrier in vertical transport MTJ structures, in all-graphene lateral spin-valves, or for spin injection and detection in silicon planar and nanowire structures.
One approach focuses on tunnel barrier injection from a ferromagnetic metal contact with detection accomplished by a second magnetic contact in a non-local spin valve geometry. A second approach focuses on polarization-dependent optical probe/analysis techniques. The transport channel may be graphene or another 2D material, or a conventional semiconductor such as silicon. Graphene is especially attractive as a transport channel due to the long spin lifetimes and diffusion lengths predicted by theory, although such values have proven a challenge to realize experimentally. One goal of this program is to understand and solve these issues. Functionalized graphene may be an important component, as it can serve as an insulating tunnel barrier, and also exhibits magnetic properties, suggesting its use as a spin injecting/detecting contact.
Extensive facilities exist for epitaxial growth, transport, magneto-optical studies, structural/magnetic characterization (e.g., AFM/MFM, magnetometry), and e-beam and photolithographic sample fabrication.
van't Erve OMJ, et al: Low resistance spin injection into silicon using graphene tunnel barriers, Nature Nanotechnology 7: 737, DOI: 10.1038/NNANO.2012.161, 2012
Cobas E, et al: Graphene as a tunnel barrier: graphene-based magnetic tunnel junctions, Nano Letters 12: 3000, DOI: 10.1021/nl3007616, 2012
van’t Erve OMJ, et al: Spin Transport and Hanle Effect in Silicon Nanowires using Graphene Tunnel Barriers, Nature Communications 6: 7541, 2015
Friedman AL, et al: Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene, ACS Nano 9: 6747, 2015
Spin injection; Spin transport; Magnetoresistance; Graphene; Silicon; Magnetic tunnel junction; Tunnel barrier; Spin valve;