Title: Crystalline Topological Semi-metals.
When: Wednesday, May 31, 2017, at 12:00.
Place: Sala de Conferencias, Módulo 00, Facultad de Ciencias, Universidad Autónoma de Madrid.
Speaker: Andreas Schnyder, Max Planck Institute for Solid State Research Stuttgart, Germany.
In this talk, I will survey recent developments regarding the topological classification of band-crossings in terms of crystal symmetries [1,2]. As concrete examples, I will discuss two topological materials: the Dirac nodal line-semi metal Ca3P2 and the anti-ferromagnet CuBi2O4.
The semi-metal Ca3P2 exhibits a line of Dirac nodes near the Fermi energy [3]. The stability of this Dirac line is guaranteed by a quantized ±π Berry phase and its low-energy physics is described by a one-parameter family of (2+1)-dimensional quantum field theories exhibiting the parity anomaly. I will show that small inversion breaking in Ca3P2 allows for an electric-field induced anomalous transverse current, whose universal component originates form the parity anomaly [4]. Due to this Hall-like current, carriers at opposite sides of the Dirac nodal ring flow to opposite surfaces when an electric field is applied. To detect the topological currents, a dumbbell device is proposed, which uses surface states to filter charges based on their momenta [4].
The anti-ferromagnet CuBi2O4 exhibits magnetic point-group symmetries as well as non-symmmorphic symmetries. I will show that the presence of non-symmorphic and off-centered mirror symmetries leads to the protection of four-fold degenerate Dirac lines [5], even for strong spin-orbit coupling. The monopole charges and the associated surface states of CuBi2O4 will be discussed in detail.
References
- C.-K. Chiu, J. C.Y. Teo, A. P. Schnyder, S. Ryu, Rev. Mod. Phys 88, 035005 (2016).
- Y. X. Zhao, A. P. Schnyder, Z. D. Wang, Phys. Rev. Lett. 116,156402 (2016).
- Y.-H. Chan, C.-K. Chiu, M. Y. Chou, A. P. Schnyder, Phys. Rev. B 93, 205132 (2016)
- W. B. Rui, Y. X. Zhao, Andreas P. Schnyder, arXiv:1703.05958, (2017).
- Y. X. Zhao, Andreas P. Schnyder, Phys. Rev. B 94, 195109 (2016).
