Excitonic instabilities in semiconductor superlattices in the lowest Landau level

In a superlattice whose unit cell contains two identical quantum wells distanced by a length b, weak tunneling is allowed to occur both intra- and inter-cell. The intra-cell tunneling leads to the splitting of the electron energy levels in two minibands separated by Delta(S AS) = E-S - E-AS, the symmetric-antisymmetric energy gap. The inter-cell tunneling broadens these minibands to a width proportional to the tunneling probability. In the presence of a magnetic field, when additional splitting of the energy levels occurs, a degeneracy between minibands of opposite spins can be realized by timing the intensity of the magnetic field and the tunneling probability. Within the Hartree-Fock approximation. we investigate the existence of excitonic instabilities that can arise when, in the lowest Landau level (n = 0), the \Sup arrow> and \Adown arrow> minibands are almost degenerate. (C) 2002 Published by Elsevier Science B.V.