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 (approximately 0.7 X 10(11) 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.