Acoustic polaron motion, solitary

DONOVAN AND WILSON Solitary Wave Acoustic Polaron Motion... 

The low field nobility of a charge carrier on a polydiacetylene chain is ultra high, and yet the drift velocity saturates at a low vaiue comparable to the sound velocity Conventional ideas applicable to conventional semiconductors cannot eiqplain these phenomena The motion is that of a Solitary Wave Acoustic Polaron (SWAP) The SWAP is characteristic of a one dimensional system The properties of the SWAP are described ... 

In ID the lattice deforms around the electron and loced.ises the electron to form a polaron. The ii portant deformation is acoustic, in udiich the density of the lattice changes optic deformations occur also but are not important in the polaron motion. The mathematical description of the polaron is like that of solitary waves. The Solitary wave Acoustic Polaron (SWAP) has a very large effective mass its kinetic velocity is small. Horeover it cannot move at a velocity greater than S as its kinetic velocity approaches S the acoustic deformation increases and the SNAP mass increases. In addition back scattering is very rare. So the SWAP kinetic and drift velocities are equal. 

Earlier than all of this Holstein (10) described his optic polaron, in which the deformation of the ID chain is an optic deformation. His was the first polaron solution which was a Solitary Wave or Soliton. In such a deformation there is no change in lattice density in the polaron there is only a rearrangement of atoms without a change of density. In the case of the optic polaron there is no analytical solution for the moving polaron. However it is clear that on increase of the optic polaron energy due to motion there is no perturbation as the velocity goes through the sound velocity. In the pure optic polaron the sound velocity is not in the model at the outset. It is in the motion of the polaron at velocities up to the sound velocity that the profound difference between the acoustic and optic polarons occurs the difference in properties of the polarons at rest is leas Important. 

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