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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:2
UID:UW-Physics-Event-4860
DTSTART:20181116T213000Z
DURATION:PT1H0M0S
DTSTAMP:20260307T061000Z
LAST-MODIFIED:20181112T154407Z
LOCATION:2241 Chamberlin Hall
SUMMARY:Terahertz frequency topological switches\, Physics Department 
 Colloquium\, Aaron Lindenberg\, Standford University
DESCRIPTION:Novel characterization techniques developed over the past 
 two decades have revolutionized our ability to visualize the microscop
 ic\, atomic-scale processes that determine the functional properties o
 f materials. The overarching challenge here is that the relevant time-
 scales and length-scales for these processes are typically 10^-13 seco
 nds (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 crystall
 ographic measurements probing dynamical switching responses in topolog
 ical Weyl semimetals.  First I will provide a brief introduction to th
 e unique aspects of these materials.  I will then show that terahertz 
 frequency light pulses can be used to induce large amplitude interlaye
 r shear oscillations with ~1% strain amplitudes\, leading to a topolog
 ically distinct metastable phase. Separate nonlinear optical measureme
 nts show that this transition is associated with a symmetry change fro
 m a non-centrosymmetric to centrosymmetric structure and therefore cor
 responds 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 annihil
 ate all Weyl points of opposite chirality.  This work defines new poss
 ibilities for ultrafast manipulation of the topological properties of 
 solids and for a topological switch operating at THz frequencies.
\n
\
 nReference:  "Time-varying shear strain as an ultrafast symmetry switc
 h in a Weyl semimetal\,” E. Sie et al.\, Nature (2018) (in press)
URL:https://www.physics.wisc.edu/events/?id=4860
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