## Abstract

It is known experimentally that at not very large filling factors the quantum Hall conductivity peaks corresponding to the same Landau level number N and two different spin orientations are well separated. These peaks occur at half-integer filling factors =2N+1/2 and =2N+3/2 so that the distance between them is unity. As increases shrinks. Near certain N=Nc two peaks merge into a single peak at =2N+1. We argue that this collapse of the spin splitting at low magnetic fields is attributed to the disorder-induced destruction of the exchange enhancement of the electron g factor. We use the mean-field approach to show that in the limit of zero Zeeman energy experiences a second-order phase transition as a function of the magnetic field. We give explicit expressions for Nc in terms of a samples parameters. For example, we predict that for high-mobility heterostructures Nc=0.9dn5/6ni-1/3, where d is the spacer width, n is the density of the two-dimensional electron gas, and ni is the two-dimensional density of randomly situated remote donors.

Original language | English (US) |
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Pages (from-to) | 17366-17378 |

Number of pages | 13 |

Journal | Physical Review B |

Volume | 52 |

Issue number | 24 |

DOIs | |

State | Published - 1995 |