Transport Properties of topological materials

Based on the topological quantum chemistry, the topological classification of materials can be explicitly identified, including the topological insulators and topological semimetals. The associated topological features are protected by the specific symmetries, such as the Dirac points protected by inversion symmetry and time-reversal symmetry. While the breaking of symmetries may lead to the transition of corresponding topological features, accompanied by the transport properties. For example, the presence of magnetic field would break the time-reversal symmetry, leading to the transition from Dirac points to Weyl points, which host nontrivial topological charges. In the moment space, the Weyl points act as the magnetic monopoles and the associated Berry curvature acts as the magnetic field, leading to the anomalous velocity of electrons and the intrinsic AHE when these is a net Berry curvature at the Fermi level. In addition to Berry curvature, further research also reveals the nonlinear Hall effect induced by the Berry curvature dipole, which does not require the breaking of time-reversal symmetry. However, it can be sensitive to the breaking of crystal symmetries, which can help probe the underlying phase transition.
This project aims to study the unconventional transport properties of topological materials, in terms of their peculiarities, like nontrivial topological charges, surface states, and nodal degeneracy, etc. For example, the three-dimensional nodal surface semimetals can exhibit instabilities when the degenerate nodal surfaces are close to the Fermi level. The 2D degenerate nodal surfaces can also exhibit different properties in the in-plane and out-of-plane directions, providing a potential platform to investigate 1D physics in 3D systems. Our research would deepen our understanding of topological materials and their interactions with external fields. In this project, the PhD candidate should have a background in physics or material science, and work in CPfS by using theoretical models and numerical tools.