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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:2
UID:UW-Physics-Event-6850
DTSTART:20220301T160000Z
DTEND:20220301T170000Z
DTSTAMP:20260414T113409Z
LAST-MODIFIED:20220213T181144Z
LOCATION:5310 Chamberlin Hall
SUMMARY:Unraveling the Bulk and  Surface Theories of Helical Higher-Or
 der Topological Insulators\, R. G. Herb Condensed Matter Seminar\, Ben
  Wieder\, MIT
DESCRIPTION:Solid-state materials including bismuth\, MoTe2\,  and BiB
 r have been predicted to be higher-order topological insulators (HOTIs
 ). In theoretical HOTI models\, the 3D bulk and 2D surfaces are gapped
 \, and odd numbers of 1D gapless topological modes appear bound to the
  hinges of finite-sized 3D samples\, providing  an indicator of the bu
 lk HOTI phase in the presence of global crystal symmetries. However\, 
 the boundaries of real material samples lack the global symmetries of 
 HOTI models\, and there exist topologically trivial models with extrin
 sic hinge states. In HOTIs
\n with chiral hinge states\, the bulk topo
 logy has been shown to be characterized by a nontrivial axion angle\, 
 and hence chiral HOTIs can in principle be characterized experimentall
 y through the framework of axion electrodynamics\, rather than higher-
 order topology.  For helical HOTIs\, however\, the bulk axion angle is
  trivial\, and the only experimental signatures proposed to date rely 
 on global symmetry arguments and hinge-state measurements.  It is henc
 e desirable to identify unambiguous bulk and surface signatures of  he
 lical HOTI phases analogous to - but distinct from - the axionic magne
 toelectric effects present in 3D topological insulators (TIs) and chir
 al HOTIs. In this talk\, I will present numerical and theoretical anal
 ysis of helical HOTIs demonstrating the existence  of quantized bulk t
 opological signatures beyond the axion angle\, placing helical HOTIs o
 n the same physical footing as well-understood 3D TIs and magnetic axi
 on insulators.​
URL:https://www.physics.wisc.edu/events/?id=6850
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