Topological and 2D materials grown by MBE: Crafting exotic physics into functional heterostructures

Seminar by Dr. Amilcar Bedoya-Pinto, Institute of Molecular Science (ICMol), University of Valencia

Place: nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian

Date: Monday, 11 September 2023, 11:00

In this talk, I will discuss how the ultra-high-vacuum growth of two-dimensional and topological materials allows the realization of fertile experimental platforms to understand and exploit exotic physical systems, particularly through epitaxial atomic engineering routes. 

In the first part, I will present the long-sought thin-film realization of an inversion-symmetry breaking Weyl Semimetal [1], a recently discovered topological material class featuring a linear electronic dispersion and degeneracy (Weyl) points that lead to peculiar open-loop surface states (Fermi-Arcs). In particular, I will show how topology and electronic structure are connected to epitaxy-dependent parameters such as strain, doping and surface termination [2]. With a careful preparation of in-situ heterostructures, I will discuss how these topological properties of Weyl Semimetal thin films can be exploited for applications in spin- orbitronics and topological superconductivity. 

In the second part, I will focus on the van-der-Waals epitaxy of a two-dimensional magnet, a CrCl3 monolayer grown on Graphene/6H-SiC(0001). In-situ X-ray magnetic circular dichroism reveals intrinsic ferromagnetic order with easy-plane anisotropy and a 2D-XY universality class [3], suggesting a Berezinskii-Kosterlitz-Thouless (BKT) phase transition in a quasi-freestanding monolayer magnet. The important role of the van der Waals substrate interaction and the underlying crystal symmetry will be discussed, thereby highlighting routes on how to control the anisotropy of 2D magnets via growth engineering. Finally, taking advantage of our all-in-situ approach, perspectives to interface 2D magnets with other functional 2D materials (ferroelectric, photoelastic) will be outlined to study novel collective phenomena in van der Waals heterostructures. 

References 

[1] Bedoya-Pinto, et.al. Realization of epitaxial NbP and TaP Weyl Semimetal thin films. ACS Nano, 14, 4405-4413 (2020) 

[2] Bedoya-Pinto, et.al. Large Fermi-energy shift and suppression of trivial surface states in Weyl Semimetal thin films. Advanced Materials 33 (21), 2008634 (2021)

[3] Bedoya-Pinto, et.al. Intrinsic 2D-XY ferromagnetism in a van der Waals monolayer. Science 374 (6567), 616- 620 (2021) 

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