To achieve the effect, researchers created a unique Hall-bar-like device of graphene-topological insulator heterostructures. Researchers believe this discovery could be used for applications in spintronic and quantum technologies. (Image credit: CC0 Public Domain)


The spin galvanic effect is a theory many have studied for years for its application to spintronics technology and potential use in the next generation of electronics. Recently, researchers at the Chalmers University of Technology in Sweden have demonstrated this effect, which allows for the conversion of non-equilibrium spin density into a charge current. By combining graphene with a topological insulator, the researchers achieved a gate-tunable spin galvanic effect at room temperature.


"We believe that this experimental realization will attract a lot of scientific attention and put topological insulators and graphene on the map for applications in spintronic and quantum technologies," said leader researcher Saroj Prasad Dash.


Graphene, a single layer of carbon atoms, has great electronic and spin transport properties. But because of the low interaction of the electron's spin and orbital angular moments, known as spin-orbit coupling, it does not reach tunable spintronic functionality in the graphene. This is where the topological insulator comes in.


The unique spin textures and the spin-momentum locking phenomenon of topological insulators make it useful for spin-orbit driven spintronics and quantum technologies. Unfortunately, this comes with its own set of challenges due to its lack of electrical gate-tunability, interference from trivial bulk states, and destruction of topological properties at heterostructure interfaces.


Researchers addressed these challenges by combining two-dimensional graphene with a three-dimensional topological insulator in van der Waals heterostructures to use their spintronic properties and create a proximity-induced spin-galvanic effect at room temperature. The thinness of the graphene allows its properties to be changed when other functional materials come in contact with it, known as the proximity effect. Graphene-based heterostructures have promising strong gate-tunability of proximity effects from its integration with other functional materials.


"To realize this spin-galvanic effect, we developed a special Hall-bar-like device of graphene-topological insulator heterostructures," says Dmitrii Khokhriakov, Ph.D. Student at QDP. The devices were built in a state-of-the-art cleanroom at the Quantum Device Physics Laboratory (QDP), the Department of Microtechnology and Nanoscience—MC2. This device allowed researchers to perform complementary measurements in different configurations through the spin switch and Hanle spin precession experiments, which resulted in the spin-galvanic effect at room temperature.


"Moreover, we were able to demonstrate a strong tunability and a sign change of the spin galvanic effect by the gate electric field, which makes such heterostructures promising for the realization of all-electrical and gate-tunable spintronic devices," concludes Saroj Prasad Dash.


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