Collective excitations of an electron Wigner lattice in double-quantum-well systems.

Abstract

The time-dependent Hartree-Fock approximation is used to study the collective excitations of an electron Wigner solid state in a double quantum well under strong magnetic fields. The electronic tunneling between the two quantum wells is taken into account explicitly. The low-lying excitations consist of an intralevel acoustic phonon and an interlevel optical phonon. When the well separation is increased beyond a certain value, a soft mode is developed in the energy spectrum of the interlevel optical phonon, indicating that the system undergoes a phase transition to a new type of density wave state. We find that independent of the electronic filling factor \ensuremath{\nu}, the position at which the soft mode occurs is always located at the symmetry point J of the first Brillouin zone.