H. A. Fertig

Collective Excitations, NMR, and Phase Transitions in Skyrme Crystals

At Landau level filling factors near ν = 1, quantum Hall ferromagnets form a Skyrme crystal state with quasi-long-range translational and noncollinear magnetic order. We develop an effective low energy theory which explains the presence of magnetic excitations in these systems at energies below the Larmor gap ( Δ) and that predicts a dramatic enhancement of the nuclear spin relaxation rate by a factor of 103. The effective theory predicts a rich set of quantum and classical phase transitions. Based in part on accurate time-dependent Hartree-Fock calculations of the ordered state collective excitation spectrum, we discuss aspects of the T-ν-Δ Skyrme crystal phase diagram.

Effective theory of Floquet topological transitions.

We develop a theory of topological transitions in a Floquet topological insulator, using graphene irradiated by circularly polarized light as a concrete realization. We demonstrate that a hallmark signature of such transitions in a static system, i.e., metallic bulk transport with conductivity of order e^{2}/h, is substantially suppressed at some Floquet topological transitions in the clean system. We determine the conditions for this suppression analytically and confirm our results in numerical simulations. Remarkably, introducing disorder dramatically enhances this transport by several orders of magnitude.

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 {nu} 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. {copyright} {ital 1997} {ital The American Physical Society}

Skyrmions without sigma models in quantum Hall ferromagnets.

We report on a microscopic theory of the Skyrmion states which occur in the quantum Hall regime. The theory is based on the identification of Skyrmion states in this system with zero-energy eigenstates of a hard-core model Hamiltonian. We find that for

UNLOCKING TRANSITION FOR MODULATED SURFACES AND QUANTUM HALL STRIPES

N_{\phi}

LAUGHLIN-JASTROW-CORRELATED WIGNER CRYSTAL IN A STRONG MAGNETIC FIELD

orbital states in a Landau level, a set of Skyrmions states with orbital degeneracy

Hamiltonian theory of the composite-fermion Wigner crystal

N_{\phi}-K

Dynamics of electrons in quantum Hall bubble phases

and spin quantum number

Critical comparison of classical field theory and microscopic wave functions for skyrmions in quantum Hall ferromagnets

S = N/2 -K

Deconfinement and dissipation in quantum Hall Josephson tunneling.

exists for each nonnegative integer