Acoustic Polaron Research Articles

The acoustic polaron via the deformation potential under the influence of a Coulombic impurity and its phase diagram

The acoustic polaron via the deformation potential under the influence of a Coulombic impurity is investigated within the modified variational scheme of the Lee-Low-Pines theory which is valid for the whole range of the electron-phonon coupling. The phase diagram obtained shows how the polaron changes its state according to the values of the electron-phonon coupling constant and of the Coulombic impurity potential.

Magnetic field dependence of cyclotron resonance linewidth for acoustic polarons in the extreme quantum limit

The magnetic field dependence of cyclotron resonance linewidth (CRLW) due to electron-acoustic phonon interactions in the extreme quantum limit is obtained on the basis of Kubo's formula and Fujita's diagram method. The 2-dimensional electron-piezoelectric phonon interaction generates a finite maximum CRLW as a function of magnetic field while CRLW for all other acoustic polarons increase with the magnetic field.

Linear energy-momentum relations for acoustic deformation-potential polarons

Several variational theories for the energy-momentum ($\mathrm{EP}$) relation of the acoustic deformation-potential (ADP) polaron are considered. We show that the trial states of these theories need not be translationally invariant to yield upper bounds to the actual $\mathrm{EP}$ relation. A theory which interpolates between weak- and strong-coupling theories is thus shown to give an asymptotically linear upper bound to the ADP polaron $\mathrm{EP}$ relation, as predicted by energy-crossing arguments.

On a Self-Trapped Acoustic Polaron with the Site Diagonal and Site Off-Diagonal Electron-Phonon Interaction

By including the site off-diagonal electron-phonon interaction which is not taken into consideration in usual, self-trapped acoustic polaron is studied generally on the basis of the complete discrete model of the classical lattice. The self-consistent equations for the polaron are solved without any assumption except that the polaron in the ground state has the same symmetry as the original crystal lattice. The following facts are shown. The effect of the site off-diagonal interaction on one center trapped state makes the polaron radius large and the lattice deformation reduced and thus the polaron unstable in comparison with that of the site diagonal interaction. Moreover, the site off-diagonal interaction makes many center trapped state more favourable than one center trapped state. The stable polaron states for various cases of trapping and the stability condition for one center trapping are discussed. Brief comment for the magnetic polaron coupled with the lattice deformation is also given.

Polaron Conductions from Band to Hopping Types. II. Hall Effect

The Hall effect of the acoustic polaron is theoretically classified into four types according to the strength of electron-phonon coupling. The first type for the weak coupling corresponds to the band conduction of large polarons. In the second type, although the small polaron is energetically stable, thermally populated large polarons play dominant role in the drift and Hall conductions. In the third type, the drift conduction is determined by the thermally activated hopping of small polarons while the Hall conduction is still due to thermally populated large polarons. In the last type for the strong coupling, the Hall conduction is also determined by the small polaron hopping. Except in the first type where the Hall to drift mobility ratio is a constant of order unity, the ratio is large compared with unity, with significant temperature dependence. The type change with increasing coupling is described in a unified treatment for polarons.