Walter Schottky Institute
Center for Nanotechnology and Nanomaterials

Topological Electronics and Materials - Research
Group leader: Dr. Christoph Kastl


ERC starting grant on Top-Down Superlattice Engineering of 2D Solid-State Quantum Matter

One of the pillars of today’s nanotechnology is the ability to precisely control the spatial symmetries and spatial extents of quantum states confined into nanostructures, either by top-down or bottom-up approaches. An intriguing case are superlattice structures, where a nanoscale periodic potential is superimposed onto the periodic atomic arrangement of a solid-state material. These superlattices give rise to artificial condensed matter phases with emergent quantum electronic properties fully controlled by the shape, magnitude and symmetry of the external potential.

Our recent ERC starting grant project "Top-Down Superlattice Engineering of 2D Solid-State Quantum Matter" investigates emergent quantum states in such nanofabricated superlattice structures. The project focuses on two-dimensional materials with strong spin-orbit coupling and non-trivial band topologies to establish their potential as functional spin-electronic and optoelectronic devices in semiconductor and quantum technologies.

2DTopS is funded through the European Union’s Horizon Europe Research and Innovation Programme under Grant Agreement No 101076915.

Control of symmetry and topology in van der Waals heterostructures

Van der Waals materials and their heterostructure are an ideal platform to engineer and explore topological states. We can control and break the relevant symmetries of the Hamiltonian at will by interfacing different van der Waals materials with different symmetries. Furthermore, we can directly address the symmetry of the electron-Bloch states in the van der Waals crystal by external electric fields in atomic field effect structures.

Currently, we explore spin-orbit and magnetic proximity interactions in graphene-based vdW heterostructures of 2D materials on a fundamental level. A major focus are the opto-spintronic and magneto-electronic properties of the heterostructures and their control via charge tuning, layer number, quality of the material interfaces, as well as the crystallographic alignment of the monolayers.

We use a set of complementary experimental techniques to interrogate the interfacial spin texture, including (ultrafast) photocurrent and Kerr microscopy as well as magnetotransport spectroscopy. For heterostructure device fabrication we employ stacking methods in controlled, inert atmosphere and standard lithography techniques. The goal of this project is to achieve a full electronic control of the band topolgy in these heterostructures.

Berry-curvature optoelectronics in topological materials

In so called Weyl semimetals, the energy bands have the topology of massless chiral fermions and they carry a quantized monopole of Berry curvature. The Berry-curvature effectively acts as a magnetic field in momentum space, and it introduces a quantum mechanical correction to the charge carrier velocity, which gives rise to new (opto)electronic phenomena, such as the non-linear anomalous Hall effect, photocurrent generation in topological metals, as well as topological Kerr effects.

In our group, we investigate the dynamics of electronic systems with large Berry curvature by ultrafast optoelectronic methods. Since Berry curvature driven effects are enhanced near small or vanishing energy gaps, our goal is to develop optoelectronic THz spectroscopy to resonantly probe the Berry curvature dynamics. Currently, we focus on van der Waals Weyl semimetals, such as WTe2 or MoTe2, wich can be integrated in micro- and nanoscale optoelectronic Thz circuits.

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