title: Observation of soft magnetorotons in bilayer quantum Hall ferromagnets.
abstract: Inelastic light-scattering measurements of low-lying collective excitations of electron double layers in the quantum Hall state at total filling nu(T)=1 reveal a deep magnetoroton in the dispersion of charge-density excitations across the tunneling gap. The roton softens and sharpens markedly when the phase boundary for transitions to highly correlated compressible states is approached. The findings are interpreted with Hartree-Fock evaluations that link soft magnetorotons to enhanced excitonic Coulomb interactions and to quantum phase transitions in the ferromagnetic bilayers.
authors.affiliation: NEST-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Luin
authors.forename: Vittorio
authors.initials: V
authors.lastname: Pellegrini
authors.forename: Aron
authors.initials: A
authors.lastname: Pinczuk
authors.forename: Brian S
authors.initials: BS
authors.lastname: Dennis
authors.forename: Loren N
authors.initials: LN
authors.lastname: Pfeiffer
authors.forename: Ken W
authors.initials: KW
authors.lastname: West