### Skyrmions in Quantum Hall Systems

Under certain conditions, two-dimensional electron systems in strong
magnetic
field behave as ``quantum Hall ferromagnets''. These unusual
ferromagnets
have the novel property that the local magnetic vorticity (or
``Skyrmion''
density) is directly related to the physical charge density. In view of
this vorticity/charge equivalence, electrical potentials couple
directly
to the magnetic vorticity.

Within the present context, a ``Skyrmion'' is a configuration of a
two-dimensional
ferromagnet which has a non-trivial global topological structure (this
Skyrmion configuration cannot be deformed into the magnetic
groundstate,
in which all spins are aligned, by a smooth or continuous process). The
importance of Skyrmions for quantum Hall systems arises from the
discovery
(based on both theoretical and experimental evidence) that they
describe
the lowest-energy charged excitations of quantum Hall ferromagnets, and
therefore dominate many of the low-temperature properties of these
systems.

Schematic illustration of a Skyrmion in a two-dimensional ferromagnet.
Many
degenerate configurations can be generated by rotating all spins
around
a fixed axis.

### Publications

*
Skyrmions in the Moore-Read state at nu=5/2
*

A. Wójs, G. Möller, S. H. Simon and N. R. Cooper

Phys. Rev. Lett. **104**, 086801 (2010) [PRL, arXiv:0910.4176]

*Dissipative Transport in Quantum Hall Ferromagnets by Spinwave
Scattering*

A. G. Green and N. R. Cooper

Phys. Rev. B **65**, 125329 (2002) [PRB, cond-mat/0201095]

*Large Skyrmions in an Al*_{0.13}Ga_{0.87}As Quantum
Well

S. P. Shukla, M. Shayegan, S. R. Parihar, S. A. Lyon, N. R. Cooper,
and A. A. Kiselev

Phys. Rev. B **61**, 4469 (2000) [PRB,
cond-mat/9908452]

*Solitary Waves in Planar Ferromagnets and the Breakdown of the
Spin-Polarized
Quantum Hall Effect*

N. R. Cooper

Phys. Rev. Lett. **80**, 4554 (1998) [PRL,
cond-mat/9801160]

*Excitonic recombination processes in Spin Polarised Two Dimensional
Electron Gases*

J. L. Osborne, A. J. Shields, M. Y. Simmons, N. R. Cooper, D. A.
Ritchie, M. Pepper

Phys. Rev. B **58**, R4227 (1998) [PRB]

*Skyrmions in Quantum Hall Systems with Realistic Force-Laws*

N. R. Cooper

Phys. Rev. B **55**, R1934 (1997) [PRB,
cond-mat/9611080]

*Theory of Photoluminescence of the nu=1 Quantum Hall State:
Excitons,
Spin-waves and Spin-textures*

N. R. Cooper and D. B. Chklovskii

Phys. Rev. B **55**, 2436 (1997) [PRB,
cond-mat/9607002].