ABSTRACT
Phonons are an important class of elementary excitations in solids. In this talk, I will discuss some recent advances that deepen our understanding of phonons. First, it was known that certain phonon modes might have a sense of chirality. We show that the phonon chirality naturally couples with the lattice chirality. Namely, in a chiral crystal, phonons with a definite chirality may propagate in only one direction. This realizes a chiral phonon diode effect. We suggest detectable effects in alpha-quartz. Second, the notions of topological states of matter have been extended to phonons. I will discuss two examples. One is the symmetry-enforced nodal chain phonons, with characters distinct from electronic systems. The other is the real Chern insulator state in phonons. For both cases, we find good material candidates that can be tested in experiments.
BIOGRAPHY
Prof. Shengyuan Yang obtained his BSc from The University of Hong Kong (2005) and Ph.D. from The University of Texas at Austin (2011). He worked as an imaging geophysicist at CGG US Services in Houston from 2011 to 2013. He joined Singapore University of Technology and Design in 2013 and is currently an associate professor there. His research works are in the field of theoretical condensed matter physics, with particular emphasis on the topological aspects of condensed matter systems.
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