Nonreciprocal Quantum Transport in Chiral Quantum Materials: from Bulk to Devices
Quantum materials with nontrivial topology (e.g., topological insulators, Dirac semimetals) have come to the forefront of solid-state research as candidate materials for low-power electronics, new magnetic memory architectures, high-performance optoelectronics, catalysis, and topological quantum computing. The concomitant development of topological quantum chemistry and successful growth of high-quality chiral crystals led to the groundbreaking prediction [1] and experimental observation of multifold fermions in the nonmagnetic B20 family of materials [2,3]. These materials possess, in addition to their chiral crystal structure, chirality in momentum space and exhibit giant spin-split Fermi-arcs and a so-called Weyl spin-momentum locking [4], which promise a rich physics playground for investigations.
![(a) Real-space schematic crystal structure of nonmagnetic chiral B20 compounds (left), and top-view (right) of the (111) plane showing the helical arrangement of atoms along the [111] crystallographic direction. (b) Reciprocal-space illustration showing the existence of multifold fermions at different high-symmetry point of the Brillouin zone (and with opposite Chern number, C). Adapted from Ref. [2]. (c) False-color image of a micrometric size device, prepared out of a FIB lamella, for electrical quantum transport. Adapted from Ref. 6.](/215128/original-1727439576.jpg?t=eyJ3aWR0aCI6MzQxLCJmaWxlX2V4dGVuc2lvbiI6ImpwZyIsIm9ial9pZCI6MjE1MTI4fQ%3D%3D--8379b788567977c8d0ed7ac29b120fd6f35e48fb "(a) Real-space schematic crystal structure of nonmagnetic chiral B20 compounds (left), and top-view (right) of the (111) plane showing the helical arrangement of atoms along the [111] crystallographic direction. (b) Reciprocal-space illustration showing the existence of multifold fermions at different high-symmetry point of the Brillouin zone (and with opposite Chern number, C). Adapted from Ref. [2]. (c) False-color image of a micrometric size device, prepared out of a FIB lamella, for electrical quantum transport. Adapted from Ref. 6.")
![(a) Real-space schematic crystal structure of nonmagnetic chiral B20 compounds (left), and top-view (right) of the (111) plane showing the helical arrangement of atoms along the [111] crystallographic direction. (b) Reciprocal-space illustration showing the existence of multifold fermions at different high-symmetry point of the Brillouin zone (and with opposite Chern number, C). Adapted from Ref. [2]. (c) False-color image of a micrometric size device, prepared out of a FIB lamella, for electrical quantum transport. Adapted from Ref. 6.](/215128/original-1727439576.jpg?t=eyJ3aWR0aCI6MjQ2LCJvYmpfaWQiOjIxNTEyOH0%3D--88f547525d0c76fb1ba2a05f916a6794fa650a9d)
Nonreciprocal transport, i.e., transport with a preferred direction, of (quasi)particles such as photons, electrons, spins, and phonons can occur in materials with broken inversion symmetry [5]. Nonreciprocal responses can further arise when time-reversal symmetry is broken by magnetic fields or spontaneous magnetic ordering, leading to effects such as the magnetochiral effect [6] and nonreciprocal magnon transport or spin currents in (chiral) magnets. In noncentrosymmetric materials, electrical transport can depart from the celebrated phenomenological Ohm’s law. Instead of a linear relation between current and electric field, a nonlinear charge current, quadratically proportional to the applied electric field, can emerge along specific crystallographic directions. If the importance of symmetries is well recognized, the underlying microscopic mechanisms underpinning specific nonreciprocal/nonlinear electronic transport responses remain to be elucidated.
Recent analytical developments in electron backscattering diffraction (EBSD) have permitted to assess the handedness (left vs. right) of crystallites and map their respective real-space distribution in chiral crystals [7], whereas focused ion beam technologies now routinely allow the patterning of selectively cut micrometric lamellae from single crystals (see panel c of the figure). This project aims to combine these techniques and probe nonreciprocal transport responses in the newly discovered class of nonmagnetic chiral B20 compounds (e.g., PdGa, PtAl, CoSi, RhSi, etc.), which host topological multifold fermions [8]; deepening our understanding of intertwined reciprocal- and real-space chirality in condensed-matter systems.
The Ph.D candidate will use state-of-the-art facilities at the Max Planck Institute for Chemical Physics of Solids in Dresden, which has decades long expertise in the synthesis of (topological) single crystals. In addition to the available characterization techniques, which include X-ray (Laue) diffraction, SQUID magnetometry, transmission electron microscopy, EBSD, and magnetotransport experiments at cryogenic temperatures (300 K - 2 K and 18 T, or down to 50 mK and 9 T), the candidate will gain access to the high magnetic field laboratory at Helmholtz-Zentrum Dresden-Rossendorf which routinely allows for 70 T pulsed magnetic fields (in special cases up to 90 T) for various measurement configurations and sample environments.
The Ph.D 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.