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UID:UW-Physics-Event-2996
DTSTART:20130509T150000Z
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DTSTAMP:20240328T143526Z
LAST-MODIFIED:20130501T204625Z
LOCATION:5310 Chamberlin
SUMMARY:Magnetization dynamics and semi-metal-insulator transition on
the surface of a topological insulator\, R. G. Herb Condensed Matter S
eminar\, Ilya Eremin\, Ruhr University Bochum
DESCRIPTION:Due to its unique properties\, topological insulators (TI)
are likely to play a major role as a component material in different
types of heterostructures. For instance\, with a view towards spintron
ics applications\, heterostructures involving ferromagnetic (FM) mater
ials and topological insulators are extensively studied both theoretic
ally and experimentally at present.
\n
\nA thin film of ferrom
agnetically ordered material proximate to the surface of a three-dimen
sional topological insulator explicitly breaks the time-reversal symme
try of the surface states. For an out-of-plane ferromagnetic order par
ameter on the surface\, parity is also broken\, since the Dirac fermio
ns become massive. This leads in turn to the generation of a Chern-Sim
ons term by quantum fluctuations. On the other hand\, for an in-plane
magnetization the surface states remain metallic.
\n
\nWe con
sider a theory for a two-dimensional interacting conduction electron s
ystem with strong spin-orbit coupling on the interface between a topol
ogical insulator and the magnetic (ferromagnetic or antiferromagnetic)
layer. For the ferromagnetic case we derive the Landau-Lifshitz equat
ion\, which features a contribution proportional to a fluctuation-indu
ced electric field obtained by computing the topological (Chern-Simons
) contribution from the vacuum polarization. We also show that fermion
ic quantum fluctuations reduce the critical temperature T*c at the int
erface relative to the critical temperature Tc of the bulk\, so that i
n the interval T*c ≤T
\n
\nIn addition we study the possibility of spontaneous breakin
g of parity due to a dynamical gap generation on the surface. We find
that in the absence of interaction between the fermions there is no sp
ontaneous gap generation. In the presence of a local\, Hubbard-like\,
interaction of strength g\, a gap and a Chern-Simons term are generate
d for g larger than some critical value provided the number of Dirac f
ermions\, N is odd. For an even number of Dirac fermions the masses ar
e generated in pairs having opposite signs\, and no Chern-Simons term
is generated. Our result offers a possible explanation to recent exper
iments showing a gap opening even when the topological insulator is pr
oximate to a planar ferromagnet.
\n
\n[1] F.S. Noguiera and Il
ya Eremin\, Phys. Rev. Lett. 109\, 237203 (2012)
\n[2] F.S. Noguie
ra and Ilya Eremin\, arXiv:1304.2933 (unpublished).
\n
URL:https://www.physics.wisc.edu/events/?id=2996
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