10 research outputs found
Charge-density-wave instability in the Holstein model with quartic anharmonic phonons
The molecular-crystal model, that describes a one-dimensional electron gas
interacting with quartic anharmonic lattice vibrations, offers great potentials
in the mapping of a relatively wide range of low-dimensional fermion systems
coupled to optical phonons onto quantum liquids with retarded interactions.
Following a non-perturbative approach involving non-Gaussian partial functional
integrations of lattice degrees of freedom, the exact expression of the
phonon-mediated two-electron action for this model is derived. With the help of
Hubbard-Stratonovich transformation the charge-density-wave instability is
examined in the sequel, with particular emphasis on the effect of the quartic
anharmonic phonons on the charge-density-wave transition temperature.Comment: 12 pages, 3 figure
Thermal lensing-induced bifocusing of spatial solitons in Kerr-type optical media
Thermo-optical effects cause a bifocusing of incoming beams in optical media,
due to the birefringence created by a thermal lens that can resolve the
incoming beams into two-component signals of different polarizations. We
propose a non-perturbative theoretical description of the process of formation
of double-pulse solitons in Kerr optical media with a thermally-induced
birefringence, based on solving simultaneously the heat equation and the
propagation equation for a beam in a one-dimensional medium with uniform heat
flux load. By means of a non-isospectral Inverse Scattering Transform assuming
an initial solution with a pulse shape, a one-soliton solution to the wave
equation is obtained that represents a double-pulse beam which characteristic
properties depend strongly on the profile of heat spatial distribution.Comment: 5 pages, 2 figure
Polarons in quantum chains with XY exchange and Dzyaloshinsky-Moriya interaction
Excitations of the polaron types are investigated in the spin-1/2 quantum chain with XY exchange and Dzyaloshinsky-Moriya interaction, both coupled to acoustic vibrations of the substrate lattice. The study is carried out via Jordan-Wigner transformation with the help of which the spin chain is mapped onto a chain of spinless fermions. From the resulting effective fermion-lattice Hamiltonian, the discrete equations of motion are derived. These equations are solved in the continuum limit for self-trapped states near the bottom of the fermion spectrum interacting with long-wavelength acoustic lattice modes. The associate polaron solution, which has a pulse shape, is shown to propagate bound to the induced lattice kink distortion by translation along the chain at a constant velocity v. The pair can also experience an additional acceleration Ď‘0 when the free fermion charge is excited above its groundstate. The polaron binding energy is strongly reduced, depending quadratically on the ratio D/J of the Dzyaloshinsky-Moriya interaction strength D to the isotropic XY exchange interaction J. It is also found that polaron parameters depend only on the XY spin-lattice coupling but not on the Dzyaloshinsky-Moriya contribution