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.

We have postdoc openings (contact: wangyao@hku.hk).

 

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 of electrons and excitons, nonlinear valley and spin currents from the Fermi pocket anisotropy, and the strong coupling between the spin, valley pseudospin with the layer pseudospin in bilayer which gives rise to magnetoelectric phenomena. Some of the predictions have already been observed.

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

 

Review

 

Spins and pseudospins in layered transition metal dichalcogenides,

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

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

 
 

Theory

 

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)

 

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)

 

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)

 

See also our related and earlier papers:

Phys. Rev. B 88, 085433 (2013). — (Link)
Phys. Rev. B 77, 235406 (2008). — (Link)

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

 
 

Collaboration with experimental groups

 

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*

http://arxiv.org/abs/1407.2645

 

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)

 

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)

 

Optical signature of symmetry variantions and spin-valley coupling in atomically thin tungsten dichalcogenides,

H. Zeng, G. Liu, J. Dai, Y. Yan, B. Zhu, R. He, L. Xie, S. Xu, X. Chen, W. Yao*, X. Cui*,

Scientific Reports 3, 1608 (2013). — (Link)

 

Valley polarization in MoS2 monolayers by optical pumping,

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

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

 

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

 
 

 

The University of Hong Kong
Department of Physics
Pokfulam Road
Hong Kong
Email:
wangyao@hku.hk
Tel: + 852-2219-4809
Fax: + 852-2559-9152