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Colloquia

Topological photonics and phononics phenomena that are not characterized by integer invariants

by Prof. Che Ting Chan (Hong Kong University of Science and Technology)

Asia/Shanghai
TDLI Meeting Room N600 (East Wing of Floor 6, North Building)

TDLI Meeting Room N600 (East Wing of Floor 6, North Building)

Description
Abstract

Recently, topological phases in photonic and phononic systems have captured the attention of scientists and engineers. These topological phases are usually classified by integers, such as Chern numbers or winding numbers. We will use some examples to illustrate that we can have topological phenomena that are not characterized by integers. In the first example, we will see how non-Abelian topological charges (that behave like matrices) can be realized in some electromagnetic and acoustic systems; and the physical consequences that will arise, including the formation of boundary modes and the constraints on degeneracy features in the bulk. In the second example, we will see that some simple photonic/phononic crystals which do not have bulk integer topological invariants behave like a "valley-Hall" topological crystal when certain boundary conditions are applied. Although the transport phenomena are almost indistinguishable from the valley-locked transport in valley-Hall crystals, the underlying principle is based on a boundary-condition induced bulk chiral anomaly, which cannot be classified using the usual topological invariants.

Biography
C.T. Chan received his PhD degree from the University of California at Berkeley in 1985.  He is currently serving as the Associate Vice-President for Research & Development at HKUST. He is also concurrently the Daniel C K Yu Professor of Science, Chair Professor of Physics, and the Director of Research Office of HKUST.
 
Chair
Prof. Qingdong Jiang
Division
Institution