Engineering topics
Chang, Po-Yao
Publications and source records attributed to Chang, Po-Yao.
A class of topological nodal rings and its realization in carbon networks
Topological nodal rings can be classified into three types according to the slopes in their energy dispersion. Type-I nodal rings consist of type-I points, type-II rings consist of type-II points, and type-III rings consist of anisotropic points. Taking carbon networks as an example, this study shows that all three types can exist and transform from one to another under experimentally realizable strain. Within a given type, a transition between a topological metal phase and a semiconductor phase also takes place, and each type of nodal rings shrinks into the corresponding type of semi-Dirac points, including novel type-II and -III semi-Dirac points. These topological features are expected to exhibit diverse electron-hole pocket patterns and Landau levels, giving rise to unusual transport properties.
Weyl-link semimetals
A family of topological semimetallic phases where twofold degenerate gapless points form linked rings is introduced here. We refer to this phase as Weyl-link semimetals. A concrete two-band model with two linked nodal lines is constructed. We demonstrate that the Chern-Simons 3-form depends on the linking number of rings in a generic two-band model. In addition, we show the emergence of zero-energy modes in the Landau level spectrum can reveal the location of nodal lines, providing a method of probing their linking number.