Professor Thorsten Hesjedal FInstP

Abstract:

Magnetotransport measurements were carried out on nanowires of the Dirac semimetal Cd3As2. Weak anti-localization was observed at 1.9 K, consistent with the presence of strong spin-orbit interaction. With decreasing temperature, Shubnikov-de Haas oscillations were seen, revealing an ultrahigh mobility of ≈57,000 cm2V−1s−1 at 1.9 K. The strong oscillations display a linear dependence of the Landau level index on the inverse of the magnetic field, yielding an intercept that is consistent with a π Berry phase — the signature feature of Dirac fermions. By studying the fundamental properties of Dirac materials, new avenues can be explored by exploiting their unique properties for spintronics and magneto-electronic devices.

Abstract:

Topological electronic materials hold great promise for revolutionizing spintronics, owing to their topological protected, spin-polarized conduction edge or surface state. One of the key bottlenecks for the practical use of common binary and ternary topological insulator (TI) materials is the large defect concentration which leads a high background carrier concentration. Elemental tin in its α-phase is a room temperature topological semimetal, which is intrinsically less prone to defect-related shortcomings. Recently, the growth of ultrathin α-Sn films on ferromagnetic Co surfaces has been achieved, however, thicker films are needed to reach the 3D topological Dirac semimetallic state. Here, the growth of α-Sn films on Co at cryogenic temperatures was explored. Very low-temperature growth holds the promise of suppressing undesired phases, alloying across the interfaces, as well as the formation of Sn pillars or hillocks. Nevertheless, the critical Sn layer thickness of ∼3 atomic layers, above which the film partially transforms into the undesired β-phase, remains the same as for room-temperature growth. From ferromagnetic resonance studies, and supported by electron microscopy, it can be concluded that for cryogenic Sn layer growth, the interface between Sn and Co remains sharp and the magnetic properties of the Co layer stay intact.