Hidden Spin Polarisations, Bulk Dirac Points, and Topological Surface States in Transition-Metal Dichalcogenides

Professor Phil King, of the School of Physics and Astronomy, University of St Andrews, will be presenting a seminar on his research.

Abstract: Transition-metal dichalcogenides (TMDs) are renowned for their rich and varied properties. They range from metals and superconductors to strongly spin-orbit-coupled semiconductors and charge-density-wave systems, with their single-layer variants one of the most prominent current examples of two-dimensional materials beyond graphene.1,2

I will report on our recent studies of these compounds from spin- and angle-resolved photoemission. I will show how a local inversion asymmetry can drive the formation of spin-polarised bulk electronic states across the 2H materials class of TMDs.3-5

This is despite the fact that global inversion symmetry is maintained in these compounds, which would usually preclude the formation of spin-splitting, pointing to new routes to circumvent conventional symmetry constraints on electronic states in solids. Furthermore, I will show that both the 1T and 2H-structured TMDs are natural hosts of ladders of type-I and type-II bulk Dirac cones and topological surface states and resonances.6,7

These naturally arise from the chalcogen p-orbital manifold as a very general consequence of their trigonal crystal field, and as such can be expected across a large number of compounds, opening routes to tune and ultimately exploit the topological physics of TMDs.

This work was performed in close collaboration with O.J. Clark, J.M. Riley, M.S. Bahramy, and colleagues from the Universities of St Andrews, Tokyo, SNU, and NTNU.

References 1. Q. H. Wang et al., Nature Nano. 7, 669 (2012). 2. X. Xu et al., Nature Phys. 10, 343 (2014). 3. J.M. Riley et al., Nature Phys. 10, 835 (2014). 4. J.M. Riley et al., Nature Nano. 10, 1043 (2015). 5. L. Bawden et al., Nature Commun. 7, 11711 (2016). 6. M.S. Bahramy, O.J. Clark et al., Nature Materials 17, 21 (2018). 7. O.J. Clark et al., Phys. Rev. Lett. 120, 156401 (2018).

Host: Dr Satoshi Sasaki (s.sasaki@leeds.ac.uk)

All are welcome to attend.