It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

Stark spectroscopy has been applied to a wide range of molecular systems and materials. A generally useful method for obtaining electronic and vibrational Stark spectra that does not require sophisticated equipment is described. By working with frozen glasses it is possible to study nearly any molecular system, including ions and proteins. Quantitative analysis of the spectra provides information on the change in dipole moment and polarizability associated with a transition. The change in dipole moment reflects the degree of charge separation for a transition, a quantity of interest to a variety of fields. The polarizability change describes the sensitivity of a transition to an electrostatic field such as that found in a protein or an ordered synthetic material. Applications to donor-acceptor polyenes, transition metal complexes (metal-to-ligand and metal-to-metal mixed valence transitions), and nonphotosynthetic biological systems are reviewed.

STARK SPECTROSCOPY: Applications in Chemistry, Biology, and Materials Science

Electron theory of the optical properties of laser-excited semiconductors

The observation of long-lived electronic coherence in photosynthetic excitation energy transfer (EET) by Engel et al. [Nature (London) 446, 782 (2007)] raises questions about the role of the protein environment in protecting this coherence and the significance of the quantum coherence in light harvesting efficiency. In this paper we explore the applicability of the Redfield equation in its full form, in the secular approximation and with neglect of the imaginary part of the relaxation terms for the study of these phenomena. We find that none of the methods can give a reliable picture of the role of the environment in photosynthetic EET. In particular the popular secular approximation (or the corresponding Lindblad equation) produces anomalous behavior in the incoherent transfer region leading to overestimation of the contribution of environment-assisted transfer. The full Redfield expression on the other hand produces environment-independent dynamics in the large reorganization energy region. A companion paper presents an improved approach, which corrects these deficiencies [A. Ishizaki and G. R. Fleming, J. Chem. Phys. 130, 234111 (2009)].

On the adequacy of the Redfield equation and related approaches to the study of quantum dynamics in electronic energy transfer

Optical properties of highly excited direct gap semiconductors

The density matrix theory is utilized for the description of ultra fast optical properties and related vibrational wave packet dynamics of molecular systems in condensed media. As an example, optically induced vibrational wave packets in the so‐called curve–crossing system are considered. Such a system goes beyond the standard treatment of optical phenomena since the vibrational wave packet moves in a double well potential and is subject to environmental influences like wave function dephasing and relaxation. The complete theoretical description has been carried out in a representation of the vibrational wave functions of the diabatic states which refer to the two coupled vibrational surfaces. Solving the corresponding density matrix equations by numerical methods allows us to incorporate the static coupling between the crossed surfaces in a nonperturbative manner. Standard projection operator technique is used to treat environmental contributions up to the second order. For the case of a bilinear couplin...

Dissipative vibrational dynamics in a curve–crossing system

The change of polariton dispersion is investigated theoretically if a large number of polaritons is present at frequencies near half the biexciton energy. A renormalization process takes place for polaritons via virtual formation of biexcitons and stimulated by the intense polariton distribution. Assuming an energetically sharp distribution as is realised e.g. by dye laser excitation the original polariton dispersion is shown to split into two new branches. These effects should manifest if e.g. an additional but weak probe light is used to testify the optical properties of the laser excited crystal. Furthermore the scattering lines of the two-photon resonance Raman process via biexcitons are characteristically modified due to both selfrenormalization of the incoming polaritons and renormalization of the scattered polaritons. Explicit results are presented for CuCl where agreement with experimental data recently published is found.



Die Veranderung der Polaritondispersion wird theoretisch fur den Fall untersucht, das eine grose Zahl von Polaritonen bei Frequenzen um die halbe Biexcitonenenergie herum vorhanden ist. Ein Renormierungsprozes fur Polaritonen uber virtuelle Biexzitonbildung findet statt und wird durch die starke Polaritonverteilung stimuliert. Unter der Annahme einer energetisch scharfen Verteilung, wie es z. B. bei der Anregung mit einem Farbstofflaser der Fall ist, wird die ursprungliche Polaritondispersion in zwei neue Zweige zerlegt. Diese Effekte sollten sich z. B. dann ausern, wenn zusatzliches schwaches Probelicht zur Untersuchung der optischen Eigenschaften des durch den Laser angeregten Kristalls benutzt wird. Weiterhin werden die Streulinien des Zwei-Photon-Resonanz-Raman-Prozesses uber Biexzitonen charakteristisch modifiziert, sowohl durch die Selbstrenormierung der einfallenden Polaritonen als auch durch die Renormierung der gestreuten Polaritonen. Explizite Resultate werden fur CuCl vorgelegt, wobei eine Ubereinstimmung mit kurzlich publizierten experimentellen Werten gefunden wird.

Renormalization of polaritons due to virtual formation of biexcitons at high densities of excitation

Density matrix theory is applied to incorporate environmental effects and, thus, dephasing and relaxation into the description of vibrational wave packet dynamics on an ultrashort time scale. Instead of calculating the density matrix in the space of vibrational coordinates, the theory is formulated in vibrational eigenstates of appropriately chosen diabatic potential energy surfaces. Although a linear coupling between the vibrational degrees of freedom of the molecular system and those of the environment has been considered in detail, any type of coupling can be studied within the presented approach. The interplay of wave packet motion on the potential energy surfaces and energy dissipation into the environment is demonstrated for two simple one-dimensional examples

Density matrix description of ultrafast dissipative wave packet dynamics

Density-matrix theory of charge transfer

Physical systems and information theory algorithms - description and nature synthetic nanostructures as quantum control systems Langmuir-Blodgett techniques spectroscopy of single molecules in solids charging effects - single-electron tunnelling dynamical repertoire of interacting networks electron motion in lateral superlattices on semiconductors controlled electronic transfer in molecular chains and segments cooperative optical properties of interacting charge transfer subunits ensemble properties and applications electric field effects on persistent spectral hole burning and applications in photonics persistent spectral hole burning and its application in optical data storage and processing holographic spectral hole burning - from data storage to information processing biomolecular electronics and optical computing bacteriorhodopsin - optical processor molecules from nature? prospects of molecular electronics.

V. May

Papers

Dissipative vibrational dynamics in a curve–crossing system

Renormalization of polaritons due to virtual formation of biexcitons at high densities of excitation

Density matrix description of ultrafast dissipative wave packet dynamics

Density-matrix theory of charge transfer

Molecular electronics : properties, dynamics, and applications