Quantum phase transitions, driven by quantum fluctuations, exhibit intriguing features offering the possibility of potentially new applications, e.g. in quantum information sciences. Major advances have been made in both theoretical and experimental investigations of the nature and behavior of quantum phases and transitions in cooperatively interacting many-body quantum systems.For modeling purposes, most of the current innovative and successful research in this field has been obta...

This book is an introduction to the quantum theory of materials and first-principles computational materials modelling. It explains how to use density functional theory as a practical tool for calculating the properties of materials without using any empirical parameters. The structural, mechanical, optical, electrical, and magnetic properties of materials are described within a single unified conceptual framework, rooted in the Schrödinger equation of quantum mechanics, and powered by den...

Condensed matter systems where interactions are strong are inherently difficult to analyze theoretically. The situation is particularly interesting in low-dimensional systems, where quantum fluctuations play a crucial role. Here, the development of non-perturbative methods and the study of integrable field theory have facilitated the understanding of the behavior of many quasi one- and two-dimensional strongly correlated systems. In view of the same rapid development that has taken place f...

The many-body-theoretical basis and applications of theoretical spectroscopy of condensed matter, e.g. crystals, nanosystems, and molecules are unified in one advanced text for readers from graduate students to active researchers in the field. The theory is developed from first principles including fully the electron-electron interaction and spin interactions. It is based on the many-body perturbation theory, a quantum-field-theoretical description, and Green's functions. The important exp...

In this thesis, magnetism and transport phenomena in spin-charge coupled systems on frustrated lattices are theoretically investigated, focusing on Ising-spin Kondo lattice models and using a combination of Monte Carlo simulation and other techniques such as variational calculations and perturbation theory. The emphasis of the study is on how the cooperation of spin-charge coupling and geometrical frustration affects the thermodynamic properties of the Kondo lattice models; it presents the...

This thesis elucidates electron correlation effects in topological matter whose electronic states hold nontrivial topological properties robust against small perturbations. In addition to a comprehensive introduction to topological matter, this thesis provides a new perspective on correlated topological matter.The book comprises three subjects, in which electron correlations in different forms are considered. The first focuses on Coulomb interactions for massless Dirac fermions. Us...

This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological insulators.The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible.The present approach uses noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one...

In this thesis, the pseudogap and the precursor superconducting state, which are of great importance in clarifying the superconductivity mechanism in high-temperature cuprate superconductors, are investigated with a c-axis optical study in YBa2(Cu1-xZnx)3Oy. Testing was performed over a wide energy range with smaller temperature intervals for several Zn-substituted samples, as well as for several carrier-doping levels.A spectral weight (SW) analysis, in which the pseudogap...

In this book, a modern unified theory of dispersion forces on atoms and bodies is presented which covers a broad range of different aspects and scenarios. Macroscopic quantum electrodynamics is applied within the context of dispersion forces. In contrast to the normal-mode quantum electrodynamics traditionally used to study dispersion forces, the new approach allows to consider realistic material properties including absorption and is flexible enough to be applied to a broad range of geome...

This textbook takes the reader on a tour of the most important landmarks of theoretical physics: classical, quantum, and statistical mechanics, relativity, electrodynamics, as well as the most modern and exciting of all: elementary particles and the physics of fractals. The second edition has been supplemented with a new chapter devoted to concise though complete presentation of dynamical systems, bifurcations and chaos theory. The treatment is confined to the essentials of each area, pres...

This work studies the magnetic behavior of ZnO nanoparticles capped with different organic molecules and showing room-temperature ferromagnetism (RTFM). Of particular significance is the combination of element-specific X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) techniques, which demonstrates the intrinsic occurrence of RTFM in these systems and indicates that it is not related to the 3-D states of the metallic cation but is relayed along the conduction...

This book introduces readers to MesoBioNano (MBN) Explorer – a multi-purpose software package designed to model molecular systems at various levels of size and complexity. In addition, it presents a specially designed multi-task toolkit and interface – the MBN Studio – which enables the set-up of input files, controls the simulations, and supports the subsequent visualization and analysis of the results obtained. The book subsequently provides a systematic description of the capabilities o...