Vertex-Correction-Driven Intersubband Spin-Density Excitonic Instability in Double Quantum Well Structures

We show that exchange-correlation induced many-body excitonic vertex correction may lead to an instability in the normal ground state of a semiconductor double quantum well structure by suppressing the symmetric-antisymmetric intersubband gap at low but accessible ({} 0.7 ×{} 10¹¹ cm^-2) electron densities. We predict as a consequence a novel electronic phase transition where the lowest intersubband spin-density-excitation gap vanishes giving rise to a new many-body triplet excitonic liquid ground state which is more stable at low densities than the usual two dimensional Fermi liquid phase.