Spin transport in graphene-based van der Waals heterostructures

The use of the spin degree of freedom for computation represents a promising approach in the field of spintronics to overcome the fundamental challenges that will be faced by the semiconductor industry the following years.

One of the major requirements for spintronics is the transport of spins over long distances at room temperature. For this purpose, graphene emerges as a wonder material, since it has the longest spin relaxation length predicted theoretically. In this thesis we use atomically flat boron nitride flakes to protect a bilayer graphene channel from environmental contamination and achieve spin relaxation lengths up to 24 micrometers at low temperatures. Moreover, to transport spins over longer distances at room temperature, we have applied charge currents to the spin transport channel to induce carrier drift and achieve spin relaxation lengths up to 90 micrometers, the longest value reported so far. The carrier drift approach also allows for the guiding of spins and we predict that it can be used for spin-based demultiplexer applications.

By studying the lifetimes for in-plane and out-of-plane spins in bilayer graphene we show that, when a small perpendicular electric field is applied, the out-of-plane lifetime becomes up to 8 times longer than the latter, making bilayer graphene even more efficient for long distance spin transport applications. Finally, we also show that, when in proximity with a transition metal dichalcogenide, monolayer graphene borrows some of its properties and spin transport also becomes anisotropic. The last findings may find applications in spin filter devices.