Citations are the number of other articles citing this article, calculated by crossref and updated daily. Box 8730, beijing 10080, china hui cao department of physics and astronomy, northwestern university, evanston, illinois 602083112 yixi liu institute of theoretical physics, academia sinica, beijing 80, china. Theory of excitoncharge transfer state coupled systems. Keeling2 1school of physics, trinity college, dublin 2, ireland 2supa, school of physics and astronomy, university of st. There are two approachesto the theory of excitons in iqls.
Publisher, academic press, original from, the university of california. Excitons are lowest excited states of the electronic subsystem of pure crystals. Chapter 7 introduction to the theory of exciton states in. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids. Download limit exceeded you have exceeded your daily download allowance. In organic materials such an overlap can not be expected as a result of the strong localition of tightly bound frenkel excitons. Although linear excitonphonon coupling has been extensively treated before, there has been little work on quadratic coupling. Andrews, ky16 9ss, united kingdom received 24 august 2012. Chargetransfer exciton states in aromatic molecular crystals. This option allows users to search by publication, volume and page selecting this option will search the current publication in context. Theory of excitons textbook binding june 1, 1963 by robert s. There are two approaches to the theory of excitons in iqls.
The author develops the effectivemass theory of excitons in lowdimensional semiconductors and describes numerical methods for calculating the optical absorption including coulomb interaction, geometry, and external fields. Excitons are selftrapped when and are large, and then the spacial size of the barrier is large compared with the lattice spacing. Theory of magnetic excitons in the heavyfermion superconductor upd 2al 3 jun chang,1 i. Absorption of light by excitons and trions in monolayers. We begin the discussion of manybody effects in crystals with the study of exciton states in semiconductors or insulators excitonic effects on the optical properties are described in chapter 12. Theory of exciton transport with quadratic excitonphonon. This chapter presents the socalled dielectric theory of the frenkel excitons.
These states, called excitons, play a large role in determining the optical properties of nonmetals. Molecular excitons may even be entirely located on the same molecule, as in fullerenes. Physics a theory of frenkel exeitons using a twolevelatom model shozo t akeno 0 mahito mabuchi 0 0 department of nuclear engineering, kyoto university, kyoto a formal, rigorous theory of frenkel excitons interacting with an external electromagnetic field is doveloped within the framework of a twolevelatom model in which the dipole approximation is employed in. These differ in the values of the wave vector k, which is defined by the relations 2 1. It takes into account the local field corrections which determine the difference between lthe ocal and mean maxwell electromagnetic field and allow for the calculation of the dielectric tensor for. Physics a theory of frenkel exeitons using a twolevelatom model shozo t akeno 0 mahito mabuchi 0 0 department of nuclear engineering, kyoto university, kyoto a formal, rigorous theory of frenkel excitons interacting with an external electromagnetic field is doveloped within the framework of a twolevelatom model in which the dipole. Distinguishing between energy and electron transfer processes in. Excitons in bulk and twodimensional semiconductors the wannier model derived in the previous chapter provides a simple framework for the inclusion of excitons in the optical properties of semiconductors. In crystals of insulators and semiconductors, when an incident photon is absorbed exciting an electron from the valence to the conduction band, a positive charged vacancy, called a hole, is created in the valence band. Exciton line shapes and migration with stochastic exciton. Pdf microscopic theory of exciton coherent control and. Absorption of light by excitons and trions in monolayers of metal dichalcogenide mos 2.
In the following section we provide a theory which accounts for the phase space lling e ects for the frenkel excitons. The chapter considers the general effectivemass theory for excitons that involves. The chapter considers the general effectivemass theory for excitons that involves the solution of a complicated set of simultaneous differential equations and a simple hydrogenic model, in which the exciton states and energies are obtained simply from a. Experiments and theory changjian zhang, haining wang, weimin chan, christina manolatou, and farhan rana school of electrical and computer engineering, cornell. These metrics are regularly updated to reflect usage leading up to the last few days. Lindblad theory of dynamical decoherence of quantumdot. In what follows, we consider excitons as bound fewanyon composites and investigate their properties in some detail. Firstprinciples exciton radiative lifetimes in wurtzite gan. Selecting this option will search all publications across the scitation platform selecting this option will search. Theory of exciton fine structure in semiconductor quantum dots. An example of wanniermott excitons exciton progression fits the expression.
A theory is developed which can treat frenkel and wannier excitons, weak vibronic coupling, and excitonexciton reactions for the rigid. In this chapter, we will evaluate the optical response for 3d and 2d semiconductors. Such a bound system of a pair of charge carriers is called an exciton. Impurities can bind excitons, and when the bound state is shallow, the oscillator strength for producing bound excitons is so high that impurity absorption can compete with intrinsic exciton absorption even at rather low impurity concentrations. An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic coulomb force. Excitons in timedependent densityfunctional theory carsten a. Excitons are excited states of the crystals, whose description lies beyond the oneelectron approximation and the band theory approach.
The excitonic collective state is a glauber coherent state, closely related to that of. Mott excitons 12 due to the overlap of the wavefunctions of di erent excitons. Pdf theory of exciton transport with quadratic exciton. A theory of secondorder absorption involving the excitation of two quasiparticles. This frenkel exciton, named after yakov frenkel, has a typical. Ullrich and zenghui yang abstract this article gives an overview of the description of the optical and dielectric properties of bulk insulators and semiconductors in timedependent densityfunctional theory tddft, with an emphasis on excitons. Such marterials like the layered transition metal dichalcogenides and monochalcogenides have attracted much interest recently, owing to their good electrical properties and high. Common terms and phrases absorption coefficient absorption lines absorption spectrum alkali halides approximation assumed atomic band gap bloch calculation chem computed conduction band coulomb interaction d. Knox, theory of excitons, academic press, new york, 1963. Nonmetallic solids have a band gap in the oneelectron picture. We present a bosonic description of excitons created by means of resonant optical pumping in a quantum well in the presence of a weak disorder potential.
Theory of electromagnetic waves in a crystal where knox, robert s. The splitting and mixing of the two bright exciton states is controlled by the long ranged. The theory is the generalization of the local field lorentz theory to the case of anisotropic molecular solids. Because is large, tunneling can be described by a continuum theory. The exciton is regarded as an elementary excitation of condensed matter that can transport energy without transporting net. If the coulomb attraction between the electron and hole is strong enough, one obtains what is called a frenkel exciton.
Variation of excess minority carriers density in function to silicon solar cell paremeters involving excitons effects. Knox, theory of excitons, academic press, new york. Davydov 1962 theory of molecular excitons mcgrawhill, new york engl. When particle interactions are considered, a large number of bound electronhole states are found within the gap. We discuss the electronic structure of excitons, their interactions with phonons and photons, and their further role of transporting excitation energy. The coupling of excitons with phonons is an important process determining the mechanism of exciton transport in molecular crystals. Fleming a a department of chemistry, university of california, berkeley and physical biosciences division, lawrence berkeley national laboratory, berkeley, ca 947201460, united states b institute of physics, savanoriu avenue 231, 02300 vilnius, lithuania. Knox, university of rochester, department of physics and astronomy, rochester, new york 146270171.
Transforming a free exciton state into a selftrapped one proceeds as a collective tunneling of coupled excitonlattice system an instanton. Article views are the countercompliant sum of full text article downloads since november 2008 both pdf and html across all institutions and individuals. This chapter discusses the properties of exciton states in semiconducting crystals largely from a theoretical point of view. See all formats and editions hide other formats and editions. It includes excitons, anyon ions18,19 which can be also treated as quasiparticleexciton complexes20, some impurity centers, etc. Excitons may be categorized with respect to the attractive interaction between the electron and hole, which in turn depends on the nature of the solid. Knox, theory of excitons supplement 5 to solid state physics, ed. In combination with gwbse theory, we prove that the excitons are of wannier type, meaning that each exciton wavefunction extends over multiple unit cells, but with extraordinarily large binding. Exciton, the combination of an electron and a positive hole an empty electron state in a valence band, which is free to move through a nonmetallic crystal as a unit because the electron and the positive hole have equal but opposite electrical charges, the exciton as a whole has no net electrical charge though it transports energy.
1042 515 1190 943 1363 1503 1324 699 802 72 217 1473 226 1248 1503 907 1265 924 165 1353 277 314 1159 189 1385 1598 632 1332 604 807 1551 617 8 1590 1632 1277 1307 1375 225 318 991 650 895 675 256