This thesis combines highly accurate optical spectroscopy data on the recently discovered iron-based high-temperature superconductors with an incisive theoretical analysis. Three outstanding results are reported: (1) The superconductivity-induced modification of the far-infrared conductivity of an iron arsenide with minimal chemical disorder is quantitatively described by means of a strong-coupling theory for spin fluctuation mediated Cooper pairing. The formalism developed in this thesis also describes prior spectroscopic data on more disordered compounds. (2) The same materials exhibit a sharp superconductivity-induced anomaly for photon energies around 2.5 eV, two orders of magnitude larger than the superconducting energy gap. The author provides a qualitative interpretation of this unprecedented observation, which is based on the multiband nature of the superconducting state. (3) The thesis also develops a comprehensive description of a superconducting, yet optically transparent iron chalcogenide compound. The author shows that this highly unusual behavior can be explained as a result of the nanoscopic coexistence of insulating and superconducting phases, and he uses a combination of two complementary experimental methods - scanning near-field optical microscopy and low-energy muon spin rotation - to directly image the phase coexistence and quantitatively determine the phase composition. These data have important implications for the interpretation of data from other experimental probes.

From fundamental physics point of view, iron-based superconductors have properties that are more amenable to band structural calculations. This book reviews the progress made in this fascinating field. With contributions from leading experts, the book provides a guide to understanding materials, physical properties, and superconductivity mechanism aspects, and is important for students and beginners to have an overall view of the recent progress in this active field.

Within this work, the pairing mechanism of conventional (Pb) and unconventional superconductors (SrFe2(As1-xPx )2 , FeSe, FeSe/STO) was investigated experimentally by means of elastic and inelastic tunneling spectroscopy at temperatures down to 30 mK. The distinction between elastic and inelastic contributions to tunneling data was elaborated. The results help to identify conventional (phonon-mediated) and unconventional (e.g. spin-?uctuation mediated) superconductivity.

This book presents the basics of superconductivity and applications of superconducting magnets. It explains the phenomenon of superconductivity, describes theories of superconductivity, and discusses type II and high-temperature cuprate superconductors. The main focus of the book is the application of superconducting magnets in accelerators, fusion reactors and other advanced applications such as nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI), high-gradient magnetic separation (HGMS), and superconducting magnetic energy storage (SMES). This new and significantly extended second edition covers the state of the art in the development of novel superconductors for advanced magnet applications, as well as the production of practical superconducting wires, tapes, and ultra high current cables used for high-field magnets. It includes two new chapters each devoted to MgB2 and Fe-based superconductors, and discusses the recently developed and world record-setting 45.5-Tesla magnetic field generated by a combination of conventional and high-temperature cuprate superconducting magnets. In addition, it discusses the status and outlook of all current and future nuclear fusion reactors worldwide. The chapter on accelerators includes the ongoing efforts to build high luminosity LHC (HL-LHC), the high-energy 28 TeV LHC (HE-LHC), the future circular collider (FCC) at CERN, and the just launched electro-ion collider (EIC) at Brookhaven National Laboratory. The book is based on the long-standing experience of the author in studying superconducting materials, building magnets and delivering numerous lectures to research scholars and students. The book provides comprehensive and fundamental knowledge in the field of applied superconductivity, greatly benefiting researchers and graduate students wishing to learn more about the various aspects of superconductivity and advanced magnet applications.

This PhD thesis reports on investigations of several oxide-based materials using advanced infrared and Raman spectroscopy techniques and in combination with external stimuli such as high magnetic or electric field, sptial confinement in thin film heterostructures and the radiation with UV light. This leads to new results in the fields of superconductivity, electronic polarization states and nanoscale phenomena. Among these, the observation of anomalous polar moments is of great relevance for understanding the electric-field-induced metal-to-insulator transistion; and the demonstration that confocal Raman spectroscopy of backfolded acoustic photons in metal-oxide multilayers can be used as a powerful characterization tool for monitoring their interface properties and layer thickness is an important technical development for the engineering of such functional oxide heterostructures.

This is the first of three volumes of the extensively revised and updated second edition of the Handbook of Superconductivity. The past twenty years have seen rapid progress in superconducting materials, which exhibit one of the most remarkable physical states of matter ever to be discovered. Superconductivity brings quantum mechanics to the scale of the everyday world where a single, coherent quantum state may extend over a distance of metres, or even kilometres, depending on the size of a coil or length of superconducting wire. Viable applications of superconductors rely fundamentally on an understanding of this intriguing phenomena and the availability of a range of materials with bespoke properties to meet practical needs. This first volume covers the fundamentals of superconductivity and the various classes of superconducting materials, which sets the context and background for Volumes 2 and 3. Key Features: Covers the depth and breadth of the field Includes contributions from leading academics and industry professionals across the world Provides hands-on guidance to the manufacturing and processing technologies A comprehensive reference, this handbook is suitable for both graduate students and practitioners in experimental physics, materials science and multiple engineering disciplines, including electronic and electrical, chemical, mechanical, metallurgy and others.

This book describes the basic physical principles of techniques to generate and ultrashort pulse lasers and applications to ultrafast spectroscopy of various materials covering chemical molecular compounds, solid-state materials, exotic novel materials including topological materials, biological molecules and bio- and synthetic polymers. It introduces non-linear optics which provides the basics of generation and measurement of pulses and application examples of ultrafast spectroscopy to solid state physics. Also it provide not only material properties but also material processing procedures. The book describes also details of the world shortest visible laser and DUV lasers developed by the author’s group. It is composed of the following 12 Sections: The special features of this book is that it is written by a single author with a few collaborators in a systematic way. Hence it provides a comprehensive and systematic description of the research field of ultrashort pulse lasers and ultrafast spectroscopy. Generation of ultrashort pulses in deep ultraviolet to near infrared Generation of ultrashort pulses in terahertz Carrier envelope phase (CEP) Simple NLO processes with a few colors Multi-color involved NLO processes Multi-color ultrashort pulse generation NLO materials NLO processes in time-resolved spectroscopy Low dimension materials Conductors and superconductors Chemical reactions and material processing Photobiological reactions

This volume presents an in-depth review of experimental and theoretical studies on the newly discovered Fe-based superconductors. Following the Introduction, which places iron-based superconductors in the context of other unconventional superconductors, the book is divided into three sections covering sample growth, experimental characterization, and theoretical understanding. To understand the complex structure-property relationships of these materials, results from a wide range of experimental techniques and theoretical approaches are described that probe the electronic and magnetic properties and offer insight into either itinerant or localized electronic states. The extensive reference lists provide a bridge to further reading. Iron-Based Superconductivity is essential reading for advanced undergraduate and graduate students as well as researchers active in the fields of condensed matter physics and materials science in general, particularly those with an interest in correlated metals, frustrated spin systems, superconductivity, and competing orders.