|
Résumé |
We propose a microscopic magneto-electric model in which the coupling
between spins and electric dipoles is mediated by lattice distortions. The
magnetic sector is described by a spin S=1/2 Heisenberg model coupled
directly to the lattice via a standard spin-Peierls term and indirectly to
the electric dipole variables via the distortion of the surrounding
electronic clouds. Electric dipoles are described by Ising variables for
simplicity. We show that the effective magneto-electric coupling which
arises due to the interconnecting lattice deformations is quite efficient in
one-dimensional arrays. More precisely, we show using bosonization and
extensive DMRG numerical simulations that increasing the magnetic field
above the spin Peierls gap, a massive polarization switch-off occurs due to
the proliferation of soliton pairs. We also analyze the effect of an
external electric field E when the magnetic system is in a gapped (plateau)
phase and show that the magnetization can be electrically switched between
clearly distinct values. More general quasi-one-dimensional models and
two-dimensional systems are also discussed. |
