Berry Phase

Variations on a theme of Aharonov and Bohm

Speaker(s): 
Sir Michael Victor Berry
Dates: 
Tuesday, September 25, 2018 - 4:30pm to 5:30pm

The Aharonov-Bohm effect (AB) concerns the role in quantum physics of the vector potential of an impenetrable line of magnetic flux. Its partial anticipation by Ehrenberg and Siday, in terms of interference, was an approximation whose wavefunction was not singlevalued, and whose connection with the singlevalued AB wave involves topology: waves winding round the flux (‘many-whirls representation’). AB is a fine illustration of idealization in physics. There are four AB effects, depending on whether the waves and the flux are classical or quantum. In the classical-classical case, many...

Tunable Berry Phase and Berry Curvature Effects in 2D and 3D Materials

Speaker(s): 
Long Ju
Dates: 
Monday, January 22, 2018 - 4:30pm to 5:30pm

Berry phase played an important role in quantum mechanics and underlying the physics of a wide range of materials from topological phases of matters to various 2D materials. While the effect of Berry phase has been extensively studied and shown through quantized electron transport experiment, the geometric aspect of wavefunction— determined by Berry curvature has remained much less understood experimentally. In this talk, I will use bilayer graphene as a model system to demonstrate effects of Berry phase and Berry curvature on materials’ electronic and optical...

The Berry Phase and the Spin Current in AFM Weyl Semimetals

Speaker(s): 
Binghai Yan
Dates: 
Wednesday, August 30, 2017 - 4:30pm to 5:30pm

The Weyl semimetal is a new topological state of matter discovered recently. It exhibits not only topologically protected surface states (similar to the topological insulator), but also fascinating charge and spin transport properties in the bulk. In this talk, I will introduce a new type of Weyl semimetal in chiral antiferromagnetic (AFM) materials, Mn3Ge and Mn3Sn [1]. They show Weyl points where bands cross linearly with large Berry phases in the band structure [2], giving rise to large anomalous Hall effect observed in recent experiments [3]. Furthermore, we have...

Magnetic Nanostructures: A Playground for Fundamental Physics

Speaker(s): 
Ran Cheng
Dates: 
Thursday, March 2, 2017 - 4:30pm to 5:30pm

Nature becomes amazingly different from what we perceive with our eyes when zoomed in to the nanometer scale, where atomic spins interact and form diverse magnetic configurations. Besides holding great technological promise, magnetic nanostructures have also enabled a vibrant playground for fundamental physics—a thriving field known as spintronics. In this talk, I will introduce selected recent progress in spintronics that has reshaped our understanding of transport phenomena occurring at the microscopic scale. Special attention will be paid to antiferromagnetic...