Yao Group @ HKU Physics


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Welcome to Yao group

We are a theoretical group working in an interdisciplinary field across condensed matter physics, quantum physics, and optical physics. Our current research interest is on quantum spintronics, and valley and spin physics in atomically thin 2D materials and their heterostructures.


Research Highlights

Valley and spin physics in 2D transition metal dichalcogenides

A trend in future electronics is to utilize internal degrees of freedom of electron, in addition to its charge, for nonvolatile information processing. Suitable candidates include the electron spin, and the valley pseudospin. The latter labels the degenerate valleys of energy bands well separated in momentum space. 2D materials, in particular the group-VI transition metal dichalcogenides, offer an exciting platform to explore valleytronics and spintronics. We have predicted a number of valley and spin dependent phenomena that make possible the generation and manipulation of valley and spin polarization and currents. These include the valley and spin dependent optical transition selection rules, the valley Hall effect and spin Hall effect, nonlinear valley and spin currents from trigonal warping, the strong coupling between the spin, valley pseudospin with the layer pseudospin in bilayer and the resultant magnetoelectric phenomena, and exciton systems with novel valley related properties in TMDs monolayers and heterobilayers. Some of the predictions have already been observed.

Below is a few selected papers we published on the topic.




Electronic structures and theoretical modelling of two-dimensional group-VIB transition metal dichalcogenides,

Guibin Liu, Di Xiao, Yugui Yao, Xiaodong Xu and Wang Yao*,

Chem. Soc. Rev. 44, 2643 (2015) — (Link).


Spins and pseudospins in layered transition metal dichalcogenides,

X. Xu*, W. Yao*, D. Xiao and T. F. Heinz,

Nature Physics 10, 343 (2014). — (Link).


Interlayer excitons in heterobilayers


Anomalous light cones and valley optical selection rules of interlayer excitons in twisted heterobilayers,

H. Yu, Y. Wang, Q. Tong, X. Xu and W. Yao*,

Phys. Rev. Lett. 115, 187002 (2015). — (Link)


Valley-Polarized Exciton Dynamics in a 2D Semiconductor Heterostructure,

P. Rivera, K. Seyler, Hongyi Yu, J. Schaibley, J. Yan, D. Mandrus, Wang Yao and X. Xu,

Science 351, 688 (2016). — (Link)


Valley optical selection rules and optical valley control


Coupled spin and valley physics in monolayers of MoS2 and other group VI dichalcogenides,

D. Xiao*, G. Liu, W. Feng, X. Xu and W. Yao*
Phys. Rev. Lett. 108, 196802 (2012). — (Link)


Magnetic control of valley pseudospin in monolayer WSe2,

G. Aivazian, Zhirui Gong, A. Jones, R. Chu, J. Yan, D. Mandrus, C. Zhang, D. Cobden, Wang Yao* and X. Xu*

Nature Physics 11, 148 (2015). — (Link)


Optical generation of excitonic valley coherence in monolayer WSe2,

A. Jones, H. Yu, N. Ghimire, S. Wu, G. Aivazian, J. Ross, B. Zhao, J. Yan, D. Mandrus, D. Xiao, W. Yao*, X. Xu*

Nature Nanotechnology 8, 634 (2013). — (Link)


Electrical Tuning of Valley Magnetic Moment via Symmetry Control in bilayer MoS2,

S. Wu, J. S. Ross, G. Liu, G. Aivazian, A. Jones, Z. Fei, W. Zhu, D. Xiao, W. Yao, D. Cobden, X. Xu,

Nature Physics 9, 149 (2013). — (Link)


Valley polarization in MoS2 monolayers by optical pumping,

H. Zeng, J. Dai, W. Yao, D. Xiao and X. Cui,

Nature Nanotechnology 7, 490 (2012). — (Link).


Media coverage: Ars Technica, Nature Nanotech. News and Views


Valley-dependent optoelectronics from inversion symmetry breaking,

W. Yao, D. Xiao and Q. Niu,
Phys. Rev. B 77, 235406 (2008). — (Link)


Valley Hall effects and valley current generation


Nonlinear valley and spin currents from Fermi pocket anisotropy in 2D crystals,

H. Yu, Y. Wu, G. Liu, X. Xu and W. Yao*,

Phys. Rev. Lett. 113, 156603 (2014). — (Link)


Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides,

H. Yu, G. Liu, P. Gong, X. Xu and W. Yao*,

Nature Communications 5, 3876 (2014). — (Link)


Valley contrasting physics in graphene: magnetic moment and topological transport,

D. Xiao*, W. Yao* and Q. Niu,

Phys. Rev. Lett. 99, 236809 (2007). — (Link)


Gate-tunable Topological Valley Transport in Bilayer Graphene,

M. Sui, G. Chen, L. Ma, W. Shan, D. Tian, K. Watanabe, T. Taniguchi, X. Jin, W. Yao, D. Xiao & Y. Zhang

Nature Physics 11, 1027 (2015). — (Link)


Interplay of spin and pseudospins


Magnetoelectric effects and valley controlled spin quantum gates in transition metal dichalcogenide bilayers,

Z. Gong, G. Liu, H. Yu, D. Xiao, X. Cui, X. Xu and W. Yao*,

Nature Communications 4, 2053 (2013). — (Link)


Spin-Layer Locking Effects in Optical Orientation of Exciton Spin in Bilayer WSe2,

A. Jones, H. Yu, J. Ross, P. Klement, N. Ghimire, J. Yan, D. Mandrus, W. Yao, X. Xu

Nature Physics 10, 130 (2014). — (Link)



The University of Hong Kong
Department of Physics
Pokfulam Road
Hong Kong
Tel: + 852-2219-4809
Fax: + 852-2559-9152