Excitonic polaron in InAs/GaAs self‐assembled quantum dot molecules

Abstract

We study the excitonic polaron formation in two InAs/GaAs coupled quantum dots. We calculate the coupling between the exciton and the LO-phonon states by using the Fröhlich Hamiltonian, from which we determine the excitonic polaron states varying the quantum dot separation. We study the dependence on the excitonic polaron formation with the coupling between the dots. Polaron formation strongly modifies the energy spectra due to the appearance of several anticrossings in the excited states.1 Introduction Various experimental and theoretical results have shown that in InAs/GaAs self assembled quantum dots (QDs) the electron are strongly coupled to longitudinal optical (LO) phonons [1,2]. The so-called electron polarons are formed due to this interaction. Many optical experiments performed on QDs involve intraband optical transitions and probe directly the polaron levels instead of purely electronic states [2][3][4]. Analogously, Far-infrared (FIR) intraband magneto-optical experiments evidence the formation of hole polarons [5]. Optical interband transitions between valence and conduction QD states include Coulomb-correlated electron-hole pairs (in short, excitons) which are electrically neutral. The coupling between LO phonons and excitons could be small since this coupling is basically electrical (Fröhlich interaction). However, recent experimental and theoretical works have demonstrated that excitons in QDs strongly couple to LO phonons in spite of their electrical neutrality [6,7]. The eigenstates of the interacting exciton and phonon systems are called excitonic polarons. In this Letter, we focus on the excitonic polaron formation in a quantum dot molecule (QDM) i. e., two coupled quantum dots. We calculate the coupling between the exciton and the LO-phonon states by using the Fröhlich Hamiltonian, from which we determine the excitonic polaron states. Polaron formation strongly modifies the optical spectra due to the appearance of several anticrossings in the excited states. We study the dependence on the excitonic polaron formation with the coupling between the dots.