The authors review the physics of ultrafast dynamics in semiconductors and their heterostructures, including both the observed experimental phenomena and the theoretical description of the processes. These are probed by ultrafast optical excitation, generating nonequilibrium states that can be monitored by time-resolved spectroscopy. Light pulses create coherent superpositions of states, and the dynamics of the associated phase relationships can be directly investigated by means of many-pulse experiments. The commonly used experimental techniques are briefly reviewed. A variety of different phenomena can be described within a common theoretical framework based on the density-matrix formalism. The important interactions of the carriers included in the theoretical description are the phonon interactions, the interactions with classical and quantum light fields, and the Coulomb interaction among the carriers themselves. These interactions give rise to a strong interplay between phase coherence and relaxation, which strongly affects the non equilibrium dynamics. Based on the general theory, the authors review the physical phenomena in various semiconductor structures including superlattices, quantum wells, quantum wires, and bulk media. Particular results which have played a central role in understanding the microscopic origins of the relaxation processes are discussed in detail.

Theory of ultrafast phenomena in photoexcited semiconductors

Many-body correlations and excitonic effects in semiconductor spectroscopy

The application of femtosecond spectroscopy to the study of ultrafast dynamics in semiconductor materials and nanostructures is reviewed with particular emphasis on the physics that can be learned from it. Excitation with ultrashort optical pulses in general results in the creation of coherent superpositions and correlated many-particle states. The review comprises a discussion of the dynamics of this correlated many-body system during and after pulsed excitation as well as its analysis by means of refined measurements and advanced theories. After an introduction of basic concepts—such as coherence, correlation and quantum kinetics—a brief overview of the most important experimental techniques and theoretical approaches is given. The remainder of this paper is devoted to specific results selected in order to highlight how femtosecond spectroscopy gives access to the physics of coherences, correlations and quantum kinetics involving charge, spin and lattice degrees of freedom.First examples deal with the dynamics of basic laser-induced coherences that can be observed, e.g. in quantum beat spectroscopy, in coherent control measurements or in experiments using few-cycle pulses. The phenomena discussed here are basic in the sense that they can be understood to a large extent on the mean-field level of the theory. Nevertheless, already on this level it is found that semiconductors behave substantially differently from atomic systems. Subsequent sections report on the occurrence of coherences and correlations beyond the mean-field level that are mediated either by carrier–phonon or carrier–carrier interactions. The corresponding analysis gives deep insight into fundamental issues such as the energy–time uncertainty, pure dephasing in quantum dot structures, the role of two-pair or even higher correlations and the build-up of screening. Finally results are presented concerning the ultrafast dynamics of resonantly coupled excitations, where a combination of different interaction mechanisms is involved in forming new types of correlations. Examples are coupled plasmon–phonon and Bloch–phonon oscillations.The results reviewed in this paper clearly reveal the central role of many-particle correlations and coherences for the ultrafast dynamics of dense semiconductor systems. Both the presence of strong correlation effects and the formation of coherences in a genuine many-particle system have important implications for the controllability of optical signals from this class of materials, which is of utmost importance for applications in present-day and future optoelectronic devices.

https://iopscience.iop.org/article/10.1088/0034-4885/67/4/R01/pdf

Femtosecond spectroscopy in semiconductors: a key to coherences, correlations and quantum kinetics

The emerging field of semiconductor quantum optics combines semiconductor physics and quantum optics, with the aim of developing quantum devices with unprecedented performance. In this book researchers and graduate students alike will reach a new level of understanding to begin conducting state-of-the-art investigations. The book combines theoretical methods from quantum optics and solid-state physics to give a consistent microscopic description of light-matter- and many-body-interaction effects in low-dimensional semiconductor nanostructures. It develops the systematic theory needed to treat semiconductor quantum-optical effects, such as strong light-matter coupling, light-matter entanglement, squeezing, as well as quantum-optical semiconductor spectroscopy. Detailed derivations of key equations help readers learn the techniques and nearly 300 exercises help test their understanding of the materials covered. The book is accompanied by a website hosted by the authors, containing further discussions on topical issues, latest trends and publications on the field. The link can be found at www.cambridge.org/9780521875097.

/pdf/semiconductor-quantum-optics-54lggd6zis.pdf

Semiconductor Quantum Optics

Decoupling of chains of equations for two-time Green's functions

Quantum mechanical kinetic equations

The two-electron correlation function, $g$, responsible for "collisional" corrections to the correlationless (or Vlasov) description of a plasma, is investigated. It is shown that an exact solution of the integral equation for $g$ can be found for a fairly wide class of spatially homogeneous, one-electron distribution functions, $f$ (the ion dynamics being neglected). This is carried out in detail for the simplest member of the class (the resonance shape), and the Landau damping of $g$ to its asymptotic ($t\ensuremath{\rightarrow}\ensuremath{\infty}$) form is exhibited explicitly. It is shown that correlations between particles separated by more than the Debye length are damped in a time which exceeds the period of plasma oscillations, ${{\ensuremath{\omega}}_{p}}^{\ensuremath{-}1}$, and that these make an appreciable contribution to the "collisional" rate of change of $f$. It is concluded that for rapidly varying $f$ (as in problems involving plasma oscillations) conventional treatments of the "collision" term should be replaced by a self-consistent solution of the coupled equations for $f$ and $g$.

Solution for the Two-Electron Correlation Function in a Plasma

: A multichannel dynamical calculation of pseudoscalar and axial vector meson parameters is performed using the relativistic Lippmann-Schwinger equation. The channel considered is PV to PV. The potential is computed using the usual Feynman rules and the resulting equations are solved on a computer. The cut-off is fixed by adjusting the output mass of one resonance or bound state or the output width to the experimental value. (Author)

H. W. Wyld

Papers

Quantum mechanical kinetic equations

Solution for the Two-Electron Correlation Function in a Plasma

Dynamical Calculations of Pseudoscalar and Axial-Vector Meson Parameters Using the Relativistic Lippmann-Schwinger Equation