arXiv subjects

A. Karlhede

Publications and source records attributed to A. Karlhede.

22 records · Page 2Linked to original sources

arXiv1997

Quantum Hall Skyrmions with Higher Topological Charge

We have investigated quantum Hall skyrmions at filling factor ν=1 carrying more than one unit of topological, and hence electric, charge. Using a combination of analytic and numerical methods we find the counterintuitive result that when the Zeeman energy is tuned to values much smaller than the interaction energy (g μ_B B/(e^2/ε\ell) < 9*10^{-5}),the creation energy of a charge two skyrmion becomes less than twice the creation energy of a charge one skyrmion, i.e. skyrmions bind in pairs. The doubly charged skyrmions are stable to further accretion of charge and exhibit a 10% larger spin per unit charge than charge one skyrmions which would, in principle, signal this pairing.

cond-mat.mes-hall↗

arXiv1996

Hartree-Fock Theory of Skyrmions in Quantum Hall Ferromagnets

We report on a study of the charged-skyrmion or spin-texture excitations which occur in quantum Hall ferromagnets near odd Landau level filling factors. Particle-hole symmetry is used to relate the spin-quantum numbers of charged particle and hole excitations and neutral particle-hole pair excitations. Hartree-Fock theory is used to provide quantitative estimates of the energies of these excitations and their dependence on Zeeman coupling strength, Landau level quantum numbers, and the thicknesses of the two-dimensional electron layers. For the case of $ν$ near three we suggest the possibility of first order phase transitions with increasing Zeeman coupling strength from a many skyrmion state to one with many maximally spin-polarized quasiparticles.

cond-mat.mes-hall↗

arXiv1996

Textured Edges in Quantum Hall Systems

We have investigated the formation of spin textures at the edges of quantum Hall systems for several ferromagnetic filling factors. The textures are driven by the same physics that leads to ``skyrmions'' in the bulk. For hard confinement and large Zeeman energies, the edges are narrow and spin polarized. Away from this limit and for $ν=1/3$, $1/5$ and $1$, we find that they widen by developing spin textures. In contrast, for $ν=3$, the edge remains spin polarized, even as it reconstructs. We comment on the mode structure of the reconstructed edges and on possible experimental signatures.

cond-mat↗

arXiv1996

A Non-linear Sigma-model for Partially Polarized QH-states

We consider a two-component quantum Hall system within a Landau-Ginzburg theory with two Chern-Simons gauge fields. From this theory we derive a sigma model covariantly coupled to one Chern-Simons field and find mean field solutions that could describe partially polarized quantum Hall states. The quasiparticles in the original model, which have quantized charge and spin, are described in the covariant sigma model by topological excitations, with the correct quantum numbers. They have finite energy due to the presence of the Chern-Simons field, and closely resemble the skyrmions in the usual non-linear sigma model. For the fully polarized states the spin is no longer quantized, but determined by Coulomb and Zeeman interactions.

cond-mat↗