Van der Waals heterostructures

Our research focuses on electronic transport in graphene-based heterostructures of 2D materials, which are held together by van der Waals forces. We study both spin and charge properties of graphene, embedded into materials such as hBN, WSe2, or magnetic 2D materials. We can further tailor its properties by applying gate voltages to nanopatterned electrodes, allowing us to create artificial superlattice potentials.

Spin transport in graphene

When a current is passed through a contact between a ferromagnet and a non-magnetic material, a spin current can enter the non-magnet simultaneously, and be detected by another ferromagnetic electrode. As graphene itself has small spin-orbit coupling, long spin lifetimes of several nanoseconds can be observed. We have studied Hanle precession around arbitrary magnetic field directions to elucidate the spin lifetime anisotropy, and found voltage-dependent spin signals in a Co/MgO/graphene spin valve. Presently we explore modifying spin transport properties in graphene by proximity contact to WSe2, which enhances its spin injection, and preparing spintronic devices from graphene and 2D ferromagnets, such as FGT.

Superlattices in graphene

A spatially periodic potential is at the heart of understanding the properties of crystalline solids. The periodic lattice need not be provided by nature, but can also by created artificially, on top of an existing crystalline material. This is called a superlattice. Here, as in natural crystals, the periodic potential leads to a band structure for electrons. We study those superlattices in high-mobility graphene embedded into boron nitride. By using thin, nanopatterned few layer graphene as a gate, we can create gate-tunable superlattices of arbitrary shape. In square superlattices, we observe the Hofstadter butterfly, a recursive band structure, and study Brown-Zak oscillations at higher temperature. In stripe superlattices (one-dimensional superlattices) we confirmed the existence of strong and robust commensurability oscillations, and are presently searching for advanced, graphene-specific band structure effects.

Proximity-induced spin-orbit coupling in graphene

As graphene itself has low spin-orbit interaction, it is the ideal transport channel for spintronics. However, we desire all-electric control of spintronic devices, which require gate-tunable spin-orbit interaction. Also, spin-orbit coupling is a central ingredient of topological insulators. When graphene is placed in close proximity to a material with heavy nuclei, such as WSe2, spin-orbit interaction is induced in graphene. We confirmed its existence by measuring weak antilocalization in those heterostructures. Presently, we are searching for a gate-tunable proximity effect, using bilayer graphene/WSe2 heterostructures.