Epitaxial thin films and heterostructures of chiral topological semimetals
Quantum materials with nontrivial topology have come to the forefront of solid-state research as candidate materials for low-power electronics, new magnetic memory architectures, high-performance optoelectronics, catalysis or topological quantum computing. The concomitant development of topological quantum chemistry and successful growth of chiral crystals led to the groundbreaking prediction and experimental realization of multifold semimetals in the nonmagnetic B20 family of materials [1, 2]. These materials possess, in addition to their chiral crystal structure, chirality in momentum-space and exhibit Fermi-arcs with maximal Chern numbers and complex spin-momentum locking [3-5]. This leads to several remarkable properties, including a giant quantized circular photogalvanic current, a chiral magnetic effect, and additional predicted but yet unobserved electronic- and spin-transport properties which are absent in other Weyl semimetals [6,7]. The optimized growth of those compounds in thin films epitaxial form, which is underway [8], will allow the control of the topological properties of these materials via film thickness, epitaxial strain, or doping. The subsequent incorporation in high-quality heterostructures, grown in vacuo, will allow the clean interfacing of those B20 semimetals with a range of other quantum materials, e.g., noncollinear antiferromagnets, ferromagnetic layers, and superconductors, for the exploration of proximity induced emergent properties (nonlinear transport responses, large spin and orbital Hall currents, spin-triplet supercurrents, etc.), which cannot be accessed in bulk crystals.
This project aims to further our understanding of this new class of nonmagnetic chiral B20 compounds which host topological multifold fermions, via the realization and study of epitaxial thin films and heterostructures; ultimately bringing us closer to prospective topological spintronics and optoelectronic devices with enhanced performance and new functionalities. The PhD candidate will use state-of-the-art facilities at the Max Planck Institute for Chemical Physics of Solids, in Dresden, to grow high-quality epitaxial thin films by magnetron sputtering on single crystalline substrates. In addition to the available characterization techniques which include X-ray diffraction, transmission electron microscopy (in collaboration with the Technical University of Dresden), SQUID magnetometry, or atomic force microscopy, the candidate is expected to perform ferromagnetic resonance spin-pumping (and inverse Spin Hall effect) measurements, as well as quantum transport experiments at cryogenic temperatures in a variety of state-of-the-art cryostats (2 K and 18 T, or 50 mK and 9 T) to gain fundamental insights into their intrinsic topological character nested in their electronic structure. The sputtering growth chambers are further connected in vacuo to a cluster including cryogenic scanning electron microscope and angle-resolved photoemission spectroscopy apparatus.
The PhD candidate should have an excellent understanding of solid-state physics and materials science, a good command of spoken and written English, and be highly motivated to work in a fast-paced, collaborative and international research environment.
