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:20240328T090950Z
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
\nelectronic properties in the presence of electric and magnet
ic
\nfields. Using group-theoretical methods\, we derive an invar
iant
\nexpansion of the Hamiltonian for electron states near the K
point of
\nthe Brillouin zone. In contrast to known materials\, i
ncluding
\nsingle-layer graphene\, any possible coupling of physic
al quantities
\nto components of the external electric field has a
counterpart where
\nthe analogous component of the magnetic field
couples to exactly the
\nsame combination of quantities. For exa
mple\, a purely electric spin
\nsplitting appears as the magneto-e
lectric analogue of the familiar
\nmagnetic Zeeman spin splitting.
The measurable thermodynamic
\nresponse induced by magnetic and
electric fields is thus completely
\nsymmetric. The Pauli magneti
zation induced by a magnetic field
\ntakes exactly the same functi
onal form as the polarization induced
\nby an electric field. Our
findings thus reveal unconventional
\nbehavior of spin and pseudo
spin degrees of freedom induced by
\nexternal fields. Although th
ey seem counterintuitive\, our findings
\nare consistent with fund
amental principles such as time reversal
\nsymmetry. For example\
, only a magnetic field can give rise to a
\nmacroscopic spin pola
rization\, whereas only a perpendicular electric
\nfield can induc
e a macroscopic polarization of the
\nsublattice-related pseudospi
n degree of freedom characterizing the
\nintravalley orbital motio
n in bilayer graphene. These rules
\nenforced by symmetry for the
matter-field interactions clarify the
\nnature of spins versus ps
eudospins. While our theoretical arguments
\nuse bilayer graphene
as an example\, they are generally valid for any
\nmaterial with
similar symmetries. The unusual equivalence of
\nmagnetic and ele
ctric fields discussed here can provide the basis
\nfor designing
more versatile device architectures for creating
\npolarizations a
nd manipulating the orientation of spins and
\npseudospins.
\n
URL:https://www.physics.wisc.edu/events/?id=3822
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