BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-3822
DTSTART:20151203T160000Z
DTEND:20151203T170000Z
DTSTAMP:20260419T110940Z
LAST-MODIFIED:20151130T202954Z
LOCATION:5310 Chamberlin Hall
SUMMARY:Electromagnetic coupling of spins and pseudospins in bilayer g
 raphene\, R. G. Herb Condensed Matter Seminar\, Prof. Roland Winkler\,
  Northern Illinois University
DESCRIPTION:We present a detailed theoretical study of bilayer-graphen
 e's<br>
\nelectronic properties in the presence of electric and magnet
 ic<br>
\nfields.  Using group-theoretical methods\, we derive an invar
 iant<br>
\nexpansion of the Hamiltonian for electron states near the K
  point of<br>
\nthe Brillouin zone. In contrast to known materials\, i
 ncluding<br>
\nsingle-layer graphene\, any possible coupling of physic
 al quantities<br>
\nto components of the external electric field has a
  counterpart where<br>
\nthe analogous component of the magnetic field
  couples to exactly the<br>
\nsame combination of quantities.  For exa
 mple\, a purely electric spin<br>
\nsplitting appears as the magneto-e
 lectric analogue of the familiar<br>
\nmagnetic Zeeman spin splitting.
   The measurable thermodynamic<br>
\nresponse induced by magnetic and 
 electric fields is thus completely<br>
\nsymmetric.  The Pauli magneti
 zation induced by a magnetic field<br>
\ntakes exactly the same functi
 onal form as the polarization induced<br>
\nby an electric field.  Our
  findings thus reveal unconventional<br>
\nbehavior of spin and pseudo
 spin degrees of freedom induced by<br>
\nexternal fields.  Although th
 ey seem counterintuitive\, our findings<br>
\nare consistent with fund
 amental principles such as time reversal<br>
\nsymmetry.  For example\
 , only a magnetic field can give rise to a<br>
\nmacroscopic spin pola
 rization\, whereas only a perpendicular electric<br>
\nfield can induc
 e a macroscopic polarization of the<br>
\nsublattice-related pseudospi
 n degree of freedom characterizing the<br>
\nintravalley orbital motio
 n in bilayer graphene.  These rules<br>
\nenforced by symmetry for the
  matter-field interactions clarify the<br>
\nnature of spins versus ps
 eudospins.  While our theoretical arguments<br>
\nuse bilayer graphene
  as an example\, they are generally valid for any<br>
\nmaterial with 
 similar symmetries.  The unusual equivalence of<br>
\nmagnetic and ele
 ctric fields discussed here can provide the basis<br>
\nfor designing 
 more versatile device architectures for creating<br>
\npolarizations a
 nd manipulating the orientation of spins and<br>
\npseudospins.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=3822
END:VEVENT
END:VCALENDAR