Dr Angadjit Singh (Department of Physics, RHUL)

The physics of band topology is indisputably recognised in condensed matter physics, with new states of matter being discovered such as Topological insulators (TIs). 3D TIs possess a massless Dirac dispersion with spin-momentum locking in the form of surface states owing to their bulk band topology. Moreover, these time reversal symmetric states can withstand external perturbations (topological protection) owing to the fact that the integer topological number is invariant under continuous deformations1. Now if spontaneous magnetisation is introduced into TIs, an exchange gap emerges, where time reversal invariance no longer holds. This inevitably led to the experimental discovery of the Quantum anomalous Hall effect (QAHE)2 where gapping or full carrier localization at the Fermi level (EF) was realized. The charge transport in this case is in the form of a chiral mode with no dissipation along the edge of a sample. My talk will briefly cover a chapter from my recently completed PhD thesis, which electrically characterised the magnetic topological insulator (MTI) - Cr doped Sb₂Te₃. I will briefly talk about their growth by molecular beam epitaxy followed by Hall measurements at 1.8 K and will comment on the mechanism of magnetism in these material systems3. Furthermore through hetero-structure engineering with other MTIs I have unravelled a large exchange bias effect which provides a way to realize exotic quantum states for spintronic and low energy magneto-electronic device applications.

1. Hasan, M. Z. & Kane, C. L. Colloquium: Topological insulators. Rev. Mod. Phys. 82, 3045–3067 (2010).
2. Chang, C.-Z. et al. Experimental Observation of the Quantum Anomalous Hall Effect in a Magnetic Topological Insulator. Science 340, 6129, 167–170 (2013).
3. Singh, A. et al.; Systematic Study of Ferromagnetism in CrxSb2-xTe3 Topological Insulator Thin Films using Electrical and Optical Techniques. Sci. Rep. 8, 17024 (2018)