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 View the MathML source, 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 tuning 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 |S↑〉 and |A↓〉 minibands are almost degenerate.