Non-linear optical response of single carrier 2-D anharmonic quantum dots Manas Ghosh, Ram Kuntal Hazra, S.P. Bhattacharyya * Department of Physical Chemistry, Indian Association for the Cultivation of Science, 2A ; B Raja S C Mullick Road, Jadavpur, Kolkata 700 032, India Received 15 June 2004; in final form 20 August 2004 Available online 15 September 2004 Abstract A linear variational route is explored for computing the first non-linear polarizability (b) of single carrier quantum dots with anharmonicity in the confinement potential. Variations in b with variations in the strength of the confining potential (x 0 ), the per- pendicular magnetic field strength (x c ) and the strength of a specific form of anharmonic coupling (k) are analyzed. A 2 · 2 model is used to predict analytically the nature of k, x c and x 0 dependence of b and compare with what is obtained from a more detailed calculation. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction The problem of designing a molecule that would dis- play a high NLO response has attracted widespread attention of both theoreticians and experimentalists. The reason is not far to seek. The targeted molecules are important in communication technology, data stor- age, optical switching, etc. [1–3]. As a result of numerous studies certain broad designing clues have emerged. Based on these guidelines most often one tries to design donor–acceptor molecules with large charge transfer from the donor to the acceptor moiety. NLO response is maximized for certain optimal combinations of charge transfer and hopping interactions and the length over which the charge is transferred [4–6]. Modulation in the molecular electronic parameters brought through subtle structural changes or change in substitution, change the electronic wavefunction and therefore the electron density distribution which ultimately shapes all the properties of atoms and molecules. It would be interesting to work on a system where one can directly tune the possible disposition of the electron density. Quantum dots present a unique possibility in this re- spect. One can tailor the energy levels and wavefunc- tions of the dots by manipulating the strength of the confining potential and its geometry together with the strength of the perpendicular magnetic field [7,8], if any. For a single carrier circular or parabolic dot, the first NLO response is expected to be zero because of symmetry. However, if a parity destroying anharmonic interaction is introduced, such single carrier dots may reveal non-zero quadratic hyperpolarizability. The ques- tion that becomes interesting at this point concerns how to get maximal NLO response from such an artificial atom. Recently, we have reported the computed pattern of variations of linear polarizability of single carrier para- bolic dots as functions of the strength of the confine- ment potential, the strength of the perpendicular magnetic field and anharmonic confining strength [9]. It would be interesting to explore the condition under which such dot atoms could display high NLO response. As we have already mentioned, one precondition for non-zero b is that the geometry of the confinement must destroy inversion symmetry. 0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.08.091 * Corresponding author. Fax: +91 33 2473 2805. E-mail address: pcspb@iacs.res.in (S.P. Bhattacharyya). www.elsevier.com/locate/cplett Chemical Physics Letters 397 (2004) 258–264