SFB 1238 | July 16, 09:00

Broken symmetries in van der Waals quantum materials

Christoph Kastl

Interfacing van der Waals materials allows manipulating the fundamental symmetries of electron states in solids with unprecedented precision using the individual layers as atomically precise, bottom-up building blocks. The resulting heterostructures have emerged as a versatile, electronically tunable solid-state platform for studying quantum phases with tailored electronic, optical, and spin properties. Here, I will discuss recent examples of intentionally and unintentionally broken symmetries in van der Waals heterointerfaces and their interrogation by non-linear optoelectronic transport [1]. In graphene-based heterostructures, we address gate-tunable, non-linear transport arising from proximity-induced spin-orbit coupling and breaking of the relevant crystal symmetries, which may be used to efficiently manipulate spin-polarized carriers by both optical and electrical means. In epitaxial graphene/Bi2Te2Se heterointerfaces with a commensurate lattice alignment, we find an enhanced helicity-dependent photocurrent, which originates from the peculiar spin-orbit proximity of the commensurate interface [1]. In graphene/WTe2 heterostructures, we demonstrate a current- induced Kerr rotation related to non-linear polarisation of the Fermi surface. We provide a theoretical model based on the non-linear anomalous Hall effect in the heterostructure, whose detection is enabled by the reduced symmetry of the incommensurate heterointerface [2]. Finally, I will outline the use of nanolithography to control the symmetry of van der Waals materials in a top-down approach. In particular, nanoscale superlattices may allow to enhance electronic correlations by flat band formation in a broad class of materials. Such correlated flat bands have non-trivial quantum geometric and topological properties that are addressable in suitable optoelectronic experiments with a resonant optical excitation. References [1] J. Kiemle, P. Zimmermann, A.W. Holleitner, C. Kastl, Light-field and spin-orbit-driven currents in van der Waals materials, Nanophotonics 2020, 9, 2693 - 2708. [2] J. Kiemle, L. Powalla, K. Polyudov, L. Gulati, M. Singh, A. W. Holleitner, M. Burghard, C. Kastl, Gate-Tunable Helical Currents in Commensurate Topological Insulator/Graphene Heterostructures, ACS Nano 2022, 16, 12338-12344. [3] L. Powalla, J. Kiemle, E. J. König, A. P. Schnyder, J. Knolle, K. Kern, A. W. Holleitner, C. Kastl, M. Burghard, Berry curvature-induced local spin polarisation in gated graphene/WTe2 heterostructures, Nat. Commun. 2022, 13, 3152.


WSI TU München
Seminar Room of the Institute of Physics II
Contact: Erwann/Matteo