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Abstract:
　　Phononic crystals are artificial periodical structures with energy bands for sound in momentum space. Dirac conic dispersions can be realized at the Brillouin zone corners of the crystals with hexagonal lattice. By reducing the symmetry of the crystals, the degeneracy at Dirac point can be lifted and a bandgap opens, and two inequivalent valleys with opposite vortex appear. The valley vortex states which carry angular momentum exert torque on particles dispersed in the fields. Breaking symmetry differently leads to phononic crystals with inverse band gaps, and when they are put together, topological one-way edge states emerge on the interfaces.

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　　Professor Zhengyou Liu received the B. Sc., M. Sc. and Ph. D degrees in physics from Wuhan University in 1986, 1989, and 1993 respectively. He joined the South China University of Technology in 1993, and moved to Wuhan University in 2001. He has been a professor under the Cheung Kong Scholars Programme of the Ministry of Education of China since 2001. He is the recipients of the China National Funds for Distinguished Young Scientists in 2004, the State Natural Science Prize of the 2nd grade in China in 2010, and the Brillouin Medal by the International Society of Phononics in 2015. He has worked on the theories on quasicrystals, phononic/photonic crystals and metamaterials, and the interaction of waves or fields with particles. He has published more than 150 peer reviewed papers, including 11 PRL, 1 Science, 1 Nature Physics, 1 Adv. Mat., with over 8300 Google Scholars citations and with H-index = 42.