11 March 2021 Thu 5 pm

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Constructing designer materials where the atomic geometry and interactions can be precisely controlled is becoming reality. I will discuss our research towards this aim using atomic manipulation by the tip of a scanning tunnelling microscope (STM) to reach the desired structures [1]. Using atomic manipulation, it is possible to construct nanostructures and lattices where every atom is in a well-defined, predetermined position. This opens possibilities for creating artificial materials with engineered electronic structure via detailed control of lattice components, symmetries and interactions. I will illustrate this concept by showing how chlorine vacancies on Cu(100) can be used to implement various one- and two-dimensional artificial lattices. In particular, I will focus on engineered topological domain wall states in one-dimensional dimer and trimer chains [2,3] and one-dimensional structures with flat bands.

In the second part of the talk, I will extend the concept of designer materials into van der Waals heterostructures, where we can realize electronic responses not found in naturally occurring materials. These limitations can be overcome in designer van der Waals (vdW) heterostructures, where the desired physics emerges from the engineered interactions between the different components. We use molecular beam epitaxy (MBE) to grow islands of ferromagnetic CrBr3 on a superconducting NbSe2 substrate. This combines out of plane ferromagnetism with Rashba spin-orbit interactions and s-wave superconductivity and allows us to realizate topological superconductivity in a van der Waals heterostructure [4]. We characterize the resulting one-dimensional edge modes using low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The use of vdW heterostructures with uniform and high-quality interfaces is promising for future device structures and further control of topological superconductivity through external stimuli (e.g. electrostatic gating).

References

[1] R. Drost, T. Ojanen, A. Harju, P. Liljeroth, Topological states in engineered atomic lattices, Nat. Phys. 13, 668 (2017).

[2] M. N. Huda, S. Kezilebieke, T. Ojanen, R. Drost, P. Liljeroth, Tuneable topological domain wall states in engineered atomic chains, npj Quant. Mater. 5, 17 (2020).

[3] M. N. Huda, S. Kezilebieke, P. Liljeroth, Designer flat bands in quasi-one-dimensional atomic lattices, Phys. Rev. Res. 2, 043426 (2020).

[4] S. Kezilebieke, M. N. Huda, V. Vaňo, M. Aapro, S. C. Ganguli, O. J. Silveira, S. Głodzik, A. S. Foster, T. Ojanen, P. Liljeroth, Topological superconductivity in a designer van der Waals heterostructure, Nature 588, 424 (2020).

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