Localized electron states induced by various disorders,including defects and impurities,usually exist in solids.Their optical properties,especially their luminescence properties,are of both scientific and technological significance.But a microscopic theory has not yet been established for such localized-state ensemble (LSE) luminescence.In this Letter,we attempt to fill this void via developing a quantum many-body (MB) luminescence theory taking into account both electron-phonon (e-p) and electron-electron (e-e) interactions.By using the developed MB-LSE theory,abnormal thermal behaviors such as redshift and subsequent blueshift of peak position,narrowing and succeeding broadening of linewidth,decline in intensity,and variation in lifetime can be quantitatively interpreted.The roles of electron-phonon and electron-electron interactions in the variable-temperature LSE luminescence are thus elucidated. Within the framework of the MB-LSE theory, moreover, Varshni's empirical formula for bandgap temperature dependence and Huang-Rhys factor for e-p coupling are further derived and discussed.
Localized electron states induced by various disorders,including defects and impurities,usually exist in solids.Their optical properties,especially their luminescence properties,are of both scientific and technological significance.But a microscopic theory has not yet been established for such localized-state ensemble (LSE) luminescence.In this Letter,we attempt to fill this void via developing a quantum many-body (MB) luminescence theory taking into account both electron-phonon (e-p) and electron-electron (e-e) interactions.By using the developed MB-LSE theory,abnormal thermal behaviors such as redshift and subsequent blueshift of peak position,narrowing and succeeding broadening of linewidth,decline in intensity,and variation in lifetime can be quantitatively interpreted.The roles of electron-phonon and electron-electron interactions in the variable-temperature LSE luminescence are thus elucidated. Within the framework of the MB-LSE theory, moreover, Varshni's empirical formula for bandgap temperature dependence and Huang-Rhys factor for e-p coupling are further derived and discussed.
A microscopic many-body theory for the optical and electronic properties of semiconductors is reviewed with an emphasis on the role of correlation effects. At the semiclassical level, the semiconductor Bloch equations include many-body effects via bandgap and field renormalization as well as correlation contributions representing two electron-hole pair amplitudes, excitonic populations, and coupled interband and intraband coherences. These Coulomb interaction induced carrier correlations lead to characteristic signatures in nonlinear semiconductor spectroscopy. At the fully quantum mechanical level the dominant light-matter correlations are described by coupled semiconductor Bloch and luminescence equations. Excitonic emission properties of quantum well and microcavity systems are discussed, including effects such as coherent signatures in the secondary emission and coherent control of the emitted light.
We study electron localization in disordered quantum systems, focusing on both individual eigenstates and thermal states. We employ complex polarization as a numerical indicator to characterize the system's localization length. Furthermore, we assess the efficacy of mean-field approximation in providing a quantitative analysis of such systems. Through this study, we seek to provide insight into the following aspects: the behavior of electron localization as a function of interaction, disorder, and temperature, whether thermal states and highly excited states exhibit similar properties in many-body localized systems, and the reliability of the mean-field approximation in weak-interaction scenarios.
The calculation of a wavefunction took about two afternoons, and five wavefunctions were calculated in the whole …. Wigner and Seitz, 1933 Summary In order to explain many important properties of materials and phenomena, it is necessary to go beyond independent-particle approximations and directly account for many-body effects that result from electronic interaction. The many-body problem is a major scientific challenge, but there has been great progress resulting from theoretical developments and advances in computation. This chapter is a short introduction to the interacting-electron problem, with some of the history that has led up to the concepts and methods described in this book. The many-body interacting-electron problem ranks among the most fascinating and fruitful areas of research in physics and chemistry. It has a rich history, starting from the early days of quantum mechanics and continuing with new intellectual challenges and opportunities. The vitality of electronic structure theory arises in large part from the close connection with experiment and applications. It is spurred on by new discoveries and advances in techniques that probe the behavior of electrons in depth. In turn, theoretical concepts and calculations can now make predictions that suggest new experiments, as well as provide quantitative information that is difficult or not yet possible to measure experimentally. This book is concerned with the effects of interactions between electrons beyond independent-particle approximations. Some phenomena cannot be explained by any independent-electron method, such as broadening and lifetime of excited states and two-particle bound states (excitons) that are crucial for optical properties of materials. There are many other examples, such as the van derWaals interaction between neutral molecules that arises from the dipole–induced dipole interaction. This force, which is entirely due to correlation between electrons, is an essential mechanism determining the functions of biological systems. Other properties, such as thermodynamically stable magnetic phases, would not exist if there were no interactions between electrons; even though mean-field approximations can describe average effects, they do not account for fluctuations around the average. Ground-state properties, such as the equilibrium structures of molecules and solids, can be described by density functional theory (DFT) and the Kohn–Sham independent-particle equations. However, present approximations are often not sufficient, and for many properties the equations, when used in a straightforward way, do not give a proper description, even in principle.
The most of the experimental measurable quantities in many-body electron system, such as the optical absorption, luminescent spectra and exciton effect, are related to the excitation states description. The density functional theory with local density approximation (DFT-LDA) as a ground state theory, i.e. the solutions based on the Kohn-Sham equation is a powerful tool for studying the ground state properties in many-particle systems. However, the first principles computation of excited states is more complexity than ground-state calculations. A key problem is that the exchange-correlation interaction in excited states is differ from the ground-states. In recent years, nevertheless, several electronic-excitation theories have been developed. The most important theoretical and computational method include the many-body perturbation theory which is based on the quasi-particle concept and the Green function equation, the time-dependent DFT and the Bethe-Salpeter equation for describing the electron-hole interaction. Among them the central ingredient is an electron's self-energy operator Σ that describes the exchange correlation effect beyond Hartree approximation. The implementations of the above theories are unavoidable to introduce some of approximations. A good approximation for Σ is the GW approach by Hedin. It is shown from computation simulations for many real condensed matter systems that the GW approach is a successful method for electronic-excitation problems. Another effective method for excited-states is so-called screen-exchange local-density approximation (sX-LDA). It is a combination of LDA and Hartree-Fock (HF)theory, in which the intrinsic local screen-exchange interaction has been replaced by a non-local one and a generalized Kohn-Sham equation (GKS) is given. Based on a PWscf package, the sX-LDA-PWscf method has been tested and indicates that an available approach for treating band-gap problem in semiconductors. In this paper, the many-body theories for the excitation process, its development and signification are reviewed. The relation and differences consist in different theoretical methods are discussed. On the based of above discussions, the applications of many-body theory to the band-band transition (band-gap underestimation problem) and exciton effect in semiconductors are presented.
The low temperature spectra of absorption and luminescence of a wide variety of impurity doped organic and inorganic solids comprise very narrow (io 1O cm1) and intense zero-phonon lines (zPL). They arise from the purely electronic transistions in the impurities i.e. from the changes of the electronic state not accompanied by creation or annihilation of the phonons of the host solid. (ZPL may be called the optical analog of the M5sbauer line), Because of their narrowness ZPL's are very sensitive to even very slight differences in the crystal fields at the 1oca tions of impurities and the ZPL spectruim of a body of impu.rities displays a large inhomogeneous broadening (formula available on paper).
Origin of the inhomogeneous linewidth in a solid state 229Th:CaF2 nuclear clock
Narrow linewidth (high-Q) quantum discriminators are essential for realizing solid-state 229Th nuclear clocks, yet the observed transition linewidths remain at the tens-to-hundreds-of-kilohertz level, far exceeding the sub-Hertz linewidth set by the radiative lifetime of the nuclear isomer. Here, we investigate the origin of this broadening in 229Th:CaF2 through systematic measurements of the linewidth as functions of temperature, thorium concentration, and quadrupole state, accompanied by theoretical analysis and first-principle simulations. We find that the linewidth is independent of temperature, increases linearly with thorium concentration, and depends strongly on the quadrupole state. Data analysis identifies variations of the local electric-field gradient (EFG) as the dominant source of inhomogeneous broadening and reveals that the EFG disorder increases linearly with thorium concentration. The observed Lorentzian line shapes and linewidth linear concentration dependence are explained naturally from the 1/r3 scaling of a random distribution of long-range dopant-induced perturbations. Complementary atomistic and \textit{ab initio} density-functional-theory calculations reproduce these characteristic features and provide insights into the microscopic defect configurations responsible for the broadening. These results establish the dominant broadening mechanism in solid-state 229Th and provide guidance for engineering nuclear-clock materials with reduced inhomogeneous broadening.