Optically driving the radiative Auger transition

In a radiative Auger process, optical decay leaves other carriers in excited states, resulting in weak red-shifted satellite peaks in the emission spectrum. The appearance of radiative Auger in the emission directly leads to the question if the process can be inverted: simultaneous photon absorption and electronic demotion. However, excitation of the radiative Auger transition has not been shown, neither on atoms nor on solid-state quantum emitters. Here, we demonstrate the optical driving of the radiative Auger transition, linking few-body Coulomb interactions and quantum optics. We perform our experiments on a trion in a semiconductor quantum dot, where the radiative Auger and the fundamental transition form a Λ-system. On driving both transitions simultaneously, we observe a reduction of the fluorescence signal by up to 70%. Our results suggest the possibility of turning resonance fluorescence on and off using radiative Auger as well as THz spectroscopy with optics close to the visible regime.

Magic Numbers in Boson 4He Clusters: The Auger Evaporation Mechanism

The absence of magic numbers in bosonic 4He clusters predicted by all theories since 1984 has been challenged by high-resolution matter-wave diffraction experiments. The observed magic numbers were explained in terms of enhanced growth rates of specific cluster sizes for which an additional excitation level calculated by diffusion Monte Carlo is stabilized. The present theoretical study provides an alternative explanation based on a simple independent particle model of the He clusters. Collisions between cluster atoms in excited states within the cluster lead to selective evaporation via an Auger process. The calculated magic numbers as well as the shape of the number distributions are in quite reasonable agreement with the experiments.

Exciton-Photon Interactions in Semiconductor Nanocrystals: Radiative Transitions, Non-Radiative Processes and Environment Effects

In this review, we discuss several fundamental processes taking place in semiconductor nanocrystals (quantum dots (QDs)) when their electron subsystem interacts with electromagnetic (EM) radiation. The physical phenomena of light emission and EM energy transfer from a QD exciton to other electronic systems such as neighbouring nanocrystals and polarisable 3D (semi-infinite dielectric or metal) and 2D (graphene) materials are considered. In particular, emission decay and FRET rates near a plane interface between two dielectrics or a dielectric and a metal are discussed and their dependence upon relevant parameters is demonstrated. The cases of direct (II–VI) and indirect (silicon) band gap semiconductors are compared. We cover the relevant non-radiative mechanisms such as the Auger process, electron capture on dangling bonds and interaction with phonons. Some further effects, such as multiple exciton generation, are also discussed. The emphasis is on explaining the underlying physics and illustrating it with calculated and experimental results in a comprehensive, tutorial manner.

Feshbach-Fano Approach for Calculation of Auger Decay Rates Using Equation-of-Motion Coupled-Cluster Wave Functions: Theory and Implementation

<p>We present a novel methodology to calculate Auger decay rates based on equation-of -motion coupled-cluster singles and doubles (EOM-CCSD) wave function, combined with a simplified continuum orbital describing the outgoing electron. In our approach the Auger process is considered as an autoionization of a resonant electronic state, which can be described with Feshbach-Fano projection technique in order to distill the resonance parameters. To this end, we employ core-valence separation (CVS) scheme as a method to extract the bound part of the decaying many-electronic state. Main advantages of our methodology include (1) flexible EOM-CCSD ansatz enabling to describe various electronic states, (2) simple, yet universal computational setup, (3) fast computations due to fully analytical evaluation of all mixed bound-continuum two-electron integrals, and (4) implementation in general-purpose software package for quantum-chemical calculations.</p>

Feshbach-Fano Approach for Calculation of Auger Decay Rates Using Equation-of-Motion Coupled-Cluster Wave Functions: Theory and Implementation

<p>We present a novel methodology to calculate Auger decay rates based on equation-of -motion coupled-cluster singles and doubles (EOM-CCSD) wave function, combined with a simplified continuum orbital describing the outgoing electron. In our approach the Auger process is considered as an autoionization of a resonant electronic state, which can be described with Feshbach-Fano projection technique in order to distill the resonance parameters. To this end, we employ core-valence separation (CVS) scheme as a method to extract the bound part of the decaying many-electronic state. Main advantages of our methodology include (1) flexible EOM-CCSD ansatz enabling to describe various electronic states, (2) simple, yet universal computational setup, (3) fast computations due to fully analytical evaluation of all mixed bound-continuum two-electron integrals, and (4) implementation in general-purpose software package for quantum-chemical calculations.</p>

Particle generation and recombination

This chapter introduces a semi-classical interpretation of particle generation and recombination using the bimolecular recombination coefficient and radiative lifetime. Particles—electrons and holes in the semiconductor—can be generated and recombine because of the multitude of energetic interactions. Radiative recombination and generation arise in the interaction with photons and can be spontaneous or stimulated. Important non-radiative processes such as the Hall-Shockley-Read process and the Auger process, which arise in multiparticle interactions, are discussed. Auger recombination is common at small bandgaps and high concentrations but also appears in large bandgap materials under high injection conditions. Impact ionization is an example of Auger generation arising from high fields. The Auger process is analyzed quantum-mechanically to show how energy and momentum conservation equations and quantum restrictions lead to the observed behavior. The chapter also discusses recombination at surfaces, which is inevitably present because of the defects and confined states arising from symmetry breaking.