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Laser Asisted Scattering of an Optical Polaron in Presence of an Impurity Center

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2012 J. Phys.: Conf. Ser. 388 132001

(http://iopscience.iop.org/1742-6596/388/13/132001)

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Laser Asisted Scattering of an Optical Polaron in Presence of an Impurity Center

S. Mukhopadhyay1 and C. Sinha 2

1Department of Physics,Brahmananda Keshab Chandra College,111/2,B.T.Road ,Calcutta – 700035,India 2 Department of Theoretical Physics, Indian Association for the Cultivation of Science, Kolkata- 700032,India

Synopsis. Momentum transfer cross-sections are studied for polarons inside a polar medium in presence of a coulomb impurity center as well as an external linerly polarised,homogeneous annd monochromatic laser field. The strongly bound polaron is found to be reluctant to contribute to the conductivity which is justified physi-cally. The present study may find application in development of electronic devices using polar materials like or-ganic semiconductors.

With the advent of nanoscale heterostruc-ture devices recently there has been increas-ingly renewed interest in phenomena associated with strong electron-phonon coupling i.e. pola-ron effect. The high degree of localization in low dimensional systems give rise to the possi-bility that in spite of a weak polar medium (e.g. GaAs), the polaron problem might show a strong coupling aspect due to confinement ef-fects[1]. In the present work we develop a theoretical approach to study the momentum transfer cross-section (MTCS) of a bound optical polaron from its ground state to a continuum state in presence of a coulomb impurity ion as well as an external laser field. This has relevance to the study of transport phenomena in a dielectric medium with impurity centers. In paricular, the MTCS is intrinsically related to the mobility via the relaxation time. Further since the impurities also have a great influence on the optical and transport properties of the materials, special at-tention is being paid to the impurity states and the impurity bound polaron, taking electron–LO phonon interactions into consideration [2,3]. The main underlying assumptions of the present prescription are i) the frequency of the laserfield is assumed to be much larger than-theoptical phonon frequency ii) The electrical-component of the laser field intensity is much below the dielectric break down limit, iii) The interaction of the electron with the phonon field is much stronger than that of the photonfield iv)

the electron- phonon coupling parameter Pα is

taken in the strong coupling region ( Pα >5.0). The variation of the MTCS with respect to Pα ,

Lω and the strength of the coulomb impurity ( β ) are studied. The present study may find application in development of electronic de-vices using polar materials like organic semi-conductors.

Figure 1. describes the MTCS versus Pα ,

the electron-phonon coupling strength for four sets of values of β (3 ,5 ,5.5 ,7 ). The curves

exhibits a peak at a definite Pα , the position of

which shifts towards smaller Pα for higher val-ues of β indicating the complementary effect of the impurity potential and the electron-phonon coupling strength on the scattering mechanism .This behavior may find applica-tions in creating materials with desired mobili-ties by controlling the above two parameters.

References

[1] Senger R T and Ercelebi A 1997 J.Phys.Condens. Matter 9 5067

[2] Mitra T K et al 1987 Physics Reports 153 91

[3] Sinha C and Mukhopadhyay S 1997 J. Phys. Condensed. Matter 9l 9597

2E-mail: tpcs@iacs.res.in

XXVII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2011) IOP PublishingJournal of Physics: Conference Series 388 (2012) 132001 doi:10.1088/1742-6596/388/13/132001

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