Neutral and Charged Spin Excitations in the Quantum Hall Ferromagnet
We present a quantum field theoretical analysis of a ν = 1 quantum Hall system, where the effective Landé g factor is small. We demonstrate the ferromagnetic nature of the ground state of the system. The effective action governing the neutral gapless ferromagnetic magnons is then obtained. The local density in the state containing these spin excitations is seen to be equal to the Pontryagin index density, which is a topological density. Apart from the usual Wess-Zumino and the O(3) sigma model terms, the effective action is seen to contain a Coulomb interaction between these topological densities as well as a Hopf term for the spin variables. Charged spin Skyrmions are seen to exist as charged excitations in the system, and it is believed that these Skyrmions are fermionic owing to the Hopf term.
KeywordsEffective Action Goldstone Boson Spin Excitation Goldstone Mode Topological Density
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