Metamaterials ’2012: The Sixth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics Optical Dynamics of a Bistable Semiconductor Quantum Dot – Metal Nanoparticle Heterodymer Bintoro S. Nugroho 1,2 Alexander A. Iskandar 3 Victor A. Malyshev 1 Jasper Knoester 1 1 Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4, 9747 AG Groningen, The Netherlands Fax: +31 50 363 4947;e-mail: j.knoester@rug.nl, v.malyshev@rug.nl 2 Faculty of Mathematics and Natural Sciences, Tanjungpura University Jl. Jendral A. Yani ,78124 Pontianak, Indonesia Fax: +31 50 363 4947; e-mail: b.nugroho@rug.nl 3 Faculty of Mathematics and Natural Science, Bandung Institute of Technology Jl. Ganesa 10, 40132 Bandung, Indonesia Fax: +62 22 2506452; e-mail: iskandar@fi.itb.ac.id Abstract We perform a theoretical study of the optical dynamics of a hybrid system comprised of a closely spaced semiconductor quantum dot (SQD) and a metal nanoparticle (MNP). We show that, depending on the strength of the SQD-MNP coupling, the system can manifest bistability in the optical response. The SQD population demonstrate a hysteresis behavior upon sweeping adiabatically up and down the input intensity. We calculate the relaxation time required for the SQD population to reach its steady- state value and show that close to a critical intensity of the input, at which the SQD population switches from a lower to a higher value, the relaxation time is slowing down dramatically. 1. Introduction Optical bistability is a fascinating nonlinear phenomenon, the essence of which is controlling the flow of light by light itself. It is of great importance for optical technologies, in particular, for optical logic and signal processing. The key ingredients for bistable response to occur are nonlinearity of the material and a positive feedback. Interplay of the two can result in a multi-valued nonlinear output within a certain range of the system parameter’s space. A generic optical bistable element exhibits two stationary stable states for the same input intensity, a property which, in principle, opens the door to applications such as all-optical switches, optical transistors, and optical memories. It is of great interest to realize this phenomenon at the nanoscale. A heterodimer comprised of an SQD and an MNP provides this possibility [1, 2, 3]. From the viewpoint of the potential use of such systems in devices, the time it takes the system to be switched from one stable state to the other is of crucial importance. Studying this time is the aim of this work. 2. Model and Formalism We consider an SQD-MNP heterodimer embedded in a dielectric host with permeability  b and driven by a linearly polarized (along the system axis) external field with amplitude E 0 and frequency ω. The optical transitions in the SQD occur between the valence band and discrete excitonic levels below the conduction band, requiring full quantum treatment. We will restrict ourselves to the transition between the valence band and the lowest exciton state. In the case of an MNP, the optical excitations are sur- face plasmons, which may be adequately described classically by its frequency dependent polarizability c  2012 Metamorphose VI ISBN 978-952-67611-2-1 - 669 -