Welcome to Prof. Qian Niu's Group
Welcome to the Niu Group: a condensed matter theory group led by Prof. Qian Niu. Our research topics cover
- Berry phase in condensed matter physics
- physics of graphene
- nanostructures and quantum devices
- semiclassical theory of Bloch electrons
- transport in magnetic systems
- anomalous Hall effect
- Bose-Einstein condensation
Universal electromotive force induced by domain wall motion
Shengyuan. A. Yang et al., PRL 102, 067201 (2009)
The electromotive force induced by a moving magnetic domain wall in a nanostrip has been calculated theoretically and detected experimentally. It is found that the emf depends only on the domain wall transformation frequency through a universal Josephson type relation, which is closely related to the topological nature of the domain wall. Our experimental measurements confirm the theoretical prediction.
Valley-contrasting physics in graphene
D. Xiao, W. Yao, and Q. Niu , PRL 99, 236809 (2007)
We investigate physical properties that can be used to distinguish the valley degree of freedom in systems where inversion symmetry is broken, using graphene systems as examples. We show that the pseudospin associated with the valley index of carriers has an intrinsic magnetic moment, in close analogy with the Bohr magneton for the electron spin. There is also a valley dependent Berry phase effect that can result in a valley contrasting Hall transport, with carriers in different valleys turning into opposite directions transverse to an in-plane electric field. These effects can be used to generate and detect valley polarization by magnetic and electric means, forming the basis for the valley-based electronics applications.