Physics Department Colloquia

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Events During the Week of November 11th through November 17th, 2018

Monday, November 12th, 2018

No events scheduled

Tuesday, November 13th, 2018

No events scheduled

Wednesday, November 14th, 2018

No events scheduled

Thursday, November 15th, 2018

No events scheduled

Friday, November 16th, 2018

Terahertz frequency topological switches
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Aaron Lindenberg, Standford University
Abstract: Novel characterization techniques developed over the past two decades have revolutionized our ability to visualize the microscopic, atomic-scale processes that determine the functional properties of materials. The overarching challenge here is that the relevant time-scales and length-scales for these processes are typically 10^-13 seconds (100 femtoseconds) and 10^-10 m (1 Angstrom) such that our view of how a material or device functions is often blurred out in time or in space. In this talk I will describe femtosecond-resolution crystallographic measurements probing dynamical switching responses in topological Weyl semimetals. First I will provide a brief introduction to the unique aspects of these materials. I will then show that terahertz frequency light pulses can be used to induce large amplitude interlayer shear oscillations with ~1% strain amplitudes, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements show that this transition is associated with a symmetry change from a non-centrosymmetric to centrosymmetric structure and therefore corresponds to a transition to a topologically trivial phase. We further show that such shear strain serves as an ultrafast, energy-efficient means to induce more robust, well-separated Weyl points or to annihilate all Weyl points of opposite chirality. This work defines new possibilities for ultrafast manipulation of the topological properties of solids and for a topological switch operating at THz frequencies. Reference: "Time-varying shear strain as an ultrafast symmetry switch in a Weyl semimetal,” E. Sie et al., Nature (2018) (in press)
Host: Jim Lawler
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