Spin Textures, Screening, and Excitations in Dirty Quantum Hall Ferromagnets

Abstract

We study quantum Hall ferromagnets in the presence of a random electrostatic impurity potential. Describing these systems with a classical nonlinear sigma model and using analytical estimates supported by results from numerical simulations, we examine the nature of the ground state as a function of disorder strength, Delta, and deviation, deltanu, of the average Landau level filling factor from unity. Screening of an impurity potential requires distortions of the spin configuration, and in the absence of Zeeman coupling there is a disorder-driven, zero-temperature phase transition from a ferromagnet at small Delta and /deltanu/ to a spin glass at larger Delta or /deltanu/. We examine ground-state response functions and excitations.

Disorder-Induced Stabilization of the Quantum Hall Ferromagnet

“…20). Increasing γ int at a fixed δν brings the system to the Skyrmion glass phase, leading to the peculiar prediction that the QHF could be destabilized in a more interacting and/or less disordered system [20,23].…”

“…In this situation, charges are introduced into the system by forming Skyrmions. In the presence of disorder, fluctuations of the impurity potential generate random potential wells which establish an optimal skyrmion size [20,25]. The QHF can resist until the Skyrmions are numerous enough to overlap, which occurs for a sufficient deviation δν from ν = 1 determined by the Skrymion size, and thus, the strength of disorder.…”

“…The horizontal dashed lines represent γint values for which sets of data were taken. The black dotted line and full circles materialized the phase boundaries between QHF and QHSG calculated in reference [20].…”

“…These considerations lead Rapsch et al to build a phase diagram where the QHF dominates the QH Skyrmion glass (QHSG) over a small optimal "window" of γ int and δν values (figure 2 in Ref. 20). Increasing γ int at a fixed δν brings the system to the Skyrmion glass phase, leading to the peculiar prediction that the QHF could be destabilized in a more interacting and/or less disordered system [20,23].…”

“…We make a quantitative comparison between our data and theory by defining the "high disorder" phase boundary at δν = 0 in Ref. 20 to match the one in Ref. 23, which occurs for a value of γ int = 1.6.…”