In the large-U limit, the ground state of the half-filled, nearest-neighbor Hubbard model on the triangular lattice is the three-sublattice antiferromagnet. In sharp contrast with the square-lattice case, where Goldstone modes never have a charge component, it is shown that beyond leading order in t/U the three Goldstone modes on the triangular lattice, at finite q, are a linear combination of spin and charge. This leads to non-vanishing conductivity at any finite frequency, even though the magnet remains insulating at zero frequency. More generally, non-collinear spin order should lead to such gapless insulating behavior.

ER - TY - Generic T1 - Charged spin-texture excitations and the Hartree-Fock approximation in the quantum Hall effect JF - Phys. Rev. B Y1 - 1994 A1 - H. A. Fertig A1 - Brey, L. A1 - René Côté A1 - A. H. MacDonald ER - TY - Generic T1 - Cooper-pair-condensate fluctuations and plasmons in layered superconductors JF - Phys. Rev. B Y1 - 1993 A1 - René Côté A1 - Griffin, A. ER - TY - Generic T1 - Edge melting and collective edge excitations of the two-dimensional Wigner crystal in a strong magnetic field JF - Phys. Rev. B Y1 - 1993 A1 - René Côté A1 - H. A. Fertig ER - TY - Generic T1 - Soft edges, reconstructions, and collective edge modes of the two-dimensional Wigner crystal JF - Phys. Rev. B Y1 - 1993 A1 - H. A. Fertig A1 - René Côté ER - TY - Generic T1 - Broken-symmetry ground states for the two-dimensional electron gas in a double-quantum-well system JF - Phys. Rev. B Y1 - 1992 A1 - René Côté A1 - Brey, L. A1 - A. H. MacDonald ER - TY - Generic T1 - Edge reconstruction and edge melting of the two-dimensional Wigner crystal in a strong magnetic field JF - Phys. Rev. Lett. Y1 - 1992 A1 - H. A. Fertig A1 - René Côté A1 - A. H. MacDonald A1 - Das Sarma, S. ER - TY - Generic T1 - Frequency-dependent conductivity of a pinned Wigner crystal JF - Surface Science Y1 - 1992 A1 - René Côté A1 - A. H. MacDonald ER - TY - Generic T1 - Collective modes of the two-dimensional Wigner crystal in a strong magnetic field JF - Phys. Rev. B Y1 - 1991 A1 - René Côté A1 - A. H. MacDonald ER - TY - Generic T1 - Coulomb effect in an optically excited electron-hole plasma of a disordered semiconductor JF - Zeitschrift fur Physik B Condensed Matter Y1 - 1990 A1 - René Côté A1 - Haug, H. AB - In this paper we extend the work of Altshuler and Aronov [1] on the effect of Coulomb interaction in disordered metals to the case of an optically generated quasi-equilibrium electron-hole plasma in a disordered semiconductor in view of its possible implications for nonlinear optics. The nonlinearity considered here arises through the optically excited plasma density. The plasma is bipolar and not necessarily degenerate as in the metallic case. The density of states and the optical spectra due to freecarrier interband transitions are numerically computed in the presence and in the absence of the Altshuler-Aronov Coulomb-disorder singularity. ER - TY - Generic T1 - Phonons as collective modes: The case of a two-dimensional Wigner crystal in a strong magnetic field JF - Phys. Rev. Lett. Y1 - 1990 A1 - René Côté A1 - A. H. MacDonald ER - TY - Generic T1 - Effect of virtual screening on the absorption spectrum of a coherently pumped semiconductor JF - Phys. Rev. B Y1 - 1989 A1 - René Côté A1 - Haug, H. ER - TY - Generic T1 - Excitonic modes in a Bose-condensed electron-hole gas in the pairing approximation JF - Phys. Rev. B Y1 - 1988 A1 - René Côté A1 - Griffin, A. ER - TY - Generic T1 - Many Body Theory of the Formation and Dynamics of Excitons in an Electron-Hole Gas at Low Temperatures JF - Japanese Journal of Applied Physics Y1 - 1987 A1 - René Côté A1 - Griffin, A. AB - Using functional differentiation to obtain the two-particle Green's functions, we give a systemmatic discussion of the collective modes in an electron-hole gas at low temperatures. Our analysis is based on the well known pairing approximation for the single particle self-energies and corresponds to the generalized RPA. The excitons with finite momentum appear as fluctuations of the electron-hole condensate and have a linear dispersion relation (Keldysh and Kozlov). ER - TY - Generic T1 - Theory of the dynamic spin response function near the Kosterlitz-Thouless transition JF - Phys. Rev. B Y1 - 1986 A1 - René Côté A1 - Griffin, Allan ER - TY - Generic T1 - Solitary wave in a magnetoelastic easy plane Heisenberg ferromagnet JF - Solid State Communications Y1 - 1983 A1 - René Côté A1 - Alain Caillé AB - The spin fluctuations of an easy plane Heisenberg ferromagnet are coupled to the transverse acoustical vibrations. In the long wavelength limit, the possibility of a solitary wave with a bell shape is analysed. It is observed that the velocity v of the solitary wave is bounded by the higher and lower velocities of the acousto-magnetic polaritons for this system. The behaviour of the solitary wave is analysed as a function of this velocity where a splitting of the solitary wave occurs at a critical velocity. ER -