Quantum Materials

An accessible overview of the concepts and tools essential to the physics of materials, with applications, exercises, and color figures.

Quantum Materials, Devices, and Applications covers the advances made in quantum technologies, both in research and mass production for applications in electronics, photonics, sensing, biomedical, environmental and agricultural applications. The book includes new materials, new device structures that are commercially available, and many more at the advanced research stage. It reviews the most relevant, current and emerging materials and device structures, organized by key applications and covers existing devices, technologies and future possibilities within a common framework of high-performance quantum devices. This book will be ideal for researchers and practitioners in academia, industry and those in materials science and engineering, electrical engineering and physics disciplines. Comprehensively covers the important and rapidly growing area of quantum technologies by focusing on current and emerging materials, devices and applications Takes an applied approach to the topic by addressing key applications in electronics, optoelectronics, photonics, sensing and the environment Addresses ethical considerations, remaining challenges and future opportunities for quantum materials and devices

This book studies the dynamics of fundamental collective excitations in quantum materials, focusing on the use of state-of-the-art ultrafast broadband optical spectroscopy. Collective behaviour in solids lies at the origin of several cooperative phenomena that can lead to profound transformations, instabilities and phase transitions. Revealing the dynamics of collective excitations is a topic of pivotal importance in contemporary condensed matter physics, as it provides information on the strength and spatial distribution of interactions and correlation. The experimental framework explored in this book relies on setting a material out-of-equilibrium by an ultrashort laser pulse and monitoring the photo-induced changes in its optical properties over a broad spectral region in the visible or deep-ultraviolet. Collective excitations (e.g. plasmons, excitons, phonons...) emerge either in the frequency domain as spectral features across the probed range, or in the time domain as coherent modes triggered by the pump pulse. Mapping the temporal evolution of these collective excitations provides access to the hierarchy of low-energy phenomena occurring in the solid during its path towards thermodynamic equilibrium. This methodology is used to investigate a number of strongly interacting and correlated materials with an increasing degree of internal complexity beyond conventional band theory.

Semiconductor nanostructures are ideal systems to tailor the physical properties via quantum effects, utilizing special growth techniques, self-assembling, wet chemical processes or lithographic tools in combination with tuneable external electric and magnetic fields. Such systems are called "Quantum Materials".The electronic, photonic, and phononic properties of these systems are governed by size quantization and discrete energy levels. The charging is controlled by the Coulomb blockade. The spin can be manipulated by the geometrical structure, external gates and by integrating hybrid ferromagnetic emitters.This book reviews sophisticated preparation methods for quantum materials based on III-V and II-VI semiconductors and a wide variety of experimental techniques for the investigation of these interesting systems. It highlights selected experiments and theoretical concepts and gives such a state-of-the-art overview about the wide field of physics and chemistry that can be studied in these systems.

This thesis focuses on the exploration of nontrivial spin dynamics in graphene-based devices and topological materials, using realistic theoretical models and state-of-the-art quantum transport methodologies. The main outcomes of this work are: (i) the analysis of the crossover from diffusive to ballistic spin transport regimes in ultraclean graphene nonlocal devices, and (ii) investigation of spin transport and spin dynamics phenomena (such as the (quantum) spin Hall effect) in novel topological materials, such as monolayer Weyl semimetals WeTe2 and MoTe2. Indeed, the ballistic spin transport results are key for further interpretation of ultraclean spintronic devices, and will enable extracting precise values of spin diffusion lengths in diffusive transport and guide experiments in the (quasi)ballistic regime. Furthermore, the thesis provides an in-depth theoretical interpretation of puzzling huge measured efficiencies of the spin Hall effect in MoTe2, as well as a prediction of a novel canted quantum spin Hall effect in WTe2 with spins pointing in the yz plane.

In topological quantum materials, quantum effects emerge at macroscopic scales and are robust to continuous changes in a material’s state. This striking synergy between quantum and topological properties is of great interest for both fundamental research and emerging technologies, especially in the fields of electronics and quantum information. This edition of the book presents a wealth of topological quantum materials, bringing together burgeoning research from different areas: topological insulators, transition metal dichalcogenides, Weyl semimetals, and unconventional and topological superconductors. The realization of the application potential of topological quantum materials requires understanding their properties at a fundamental level. This brings us back to the discovery of topological phases of matter, which earned the Nobel Prize in Physics in 2016. This book explores the connection between pioneering work on topological phases of matter and a flurry of activity that followed. The topics covered include the quantum anomalous and spin Hall effects, emergent axion electrodynamics and topological magnetoelectric effects, Weyl nodes and surface Fermi arcs, weak antilocalization, induced triplet superconductivity, Majorana fermion modes, and the fractional Josephson effect.

In the past four decades, there has been growing interest in the exciting new topic of physics in low dimensions. Thousands of original ideas have been proposed in the literature, and some are confirmed experimentally, along with several Nobel prizes which have been awarded in this field. While there are several books available, almost all are technical and accessible only to expert researchers. This book provides an accessible introduction to the field, with less emphasis on technical details. Whilst this book does not provide a traditional history of nano-science, instead it uses simple explanations and case studies as vehicles to explain key discoveries and the importance of them, enabling readers without a background in the area to gain an understanding of some aspects of nanoscale physics. It will be of interest to researchers working in condensed matter physics, in addition to engineers and advanced students in those disciplines. It also remains accessible to ‘physics enthusiasts’ from other academic disciplines, as technical details are contained within boxes and footnotes which can be skipped for a general reading of the book. Features: - Provides an accessible introduction to a technical subject - Contains exciting developments from the cutting-edge science being conducted in the area - Authored by a recognised expert in the field

Despite a long tradition of sophisticated, creative materials synthesis among quantum materials researchers, a sense of broader community has been lacking. In initiating the Fundamentals of Quantum Materials Winter School held annually at the University of Maryland, we wanted to bring together the next generation of growers to learn techniques and pointers directly from senior scientists, and it turns out that we were not alone. The enthusiasm from both students and teachers has been both gratifying and invigorating. Four schools later, we can confidently say that physicists, chemists, and materials scientists, experimentalists and theorists alike, all want to know how to make a good sample. With this in mind, we asked our lecturers to record their most important ideas and share their expertise with a broader audience. This resource is a compilation of fundamental and practical guides on the modern methods of materials synthesis utilized by these experts. We hope that you enjoy reading their essential guidance and state-of-the-art techniques as you explore the Fundamentals of Quantum Materials.