Exploration and Application of Emerging Superconducting Materials

Dear Colleagues,

In 1986, the copper-perovskite ceramic material La−Ba−Cu−O, with a critical temperature (T_c) of 36 K, was discovered. J. G. Bednorz and K. A. Müller were awarded the Nobel Prize in physics for this research. In 1987, in the system RE−Ba−Cu−O (RE—rare earth element), La was replaced with Y by another, smaller element, and superconducting transition was obtained at a T_c of 92 − 94 K. Research in the following years led to the discovery of several families of superconductors from the group of cuprates, e.g., Bi−Sr−Ca−Cu−O, Tl−Ba−Ca−Cu−O, and Hg−Ba−Ca−Cu−O, where Cu−O planes are responsible for superconductivity. In this class of superconductors, the highest T_c of 134 K was reached by HgBa₂Ca₂Cu₃O₉ compound at ambient pressure, and 164 K at 30 GPa. At the end of 2019, researchers at the Max-Planck Institute for Chemistry in Mainz (Germany) approached a 250 K transition temperature for the superconductor LaH₁₀ at 170 GPa.

Solid-state physics efforts aim to understand the physical mechanisms of high-temperature superconductivity (HTS). Research on unconventional HTS will include modeling of the transport and magnetoelectric properties, calculations of dynamic conductivity and the dependence of the relaxation function on temperature, the temperature dependence of various transport coefficients, and attempts to explain how electron–phonon scattering affects the electron spectrum, conductivity, and Raman scattering. Recently, researchers have focused on cooper-free superconductors, e.g., Ba−K−Bi−O with T_c = 39 K, in which the phononic mechanism is responsible for superconductivity; research on these compounds is of interest to researchers.

HTS is of great technological importance, although the dream of superconductivity at room temperature has still not been fulfilled, despite recent reports. Extremely useful applications of HTS include the energy transport cable industry, as well as ambitious projects involving motors with superconducting magnets, e.g., at CERN, Josephson junctions, SQUIDs (superconducting quantum interference devices), quantum computers, as well as the space industry, e.g., superconducting foams and tapes. Learning about the basic properties of HTS, modeling, and the synthesis of materials with specific physico-chemical parameters and shapes (techniques using 3D printing) has a significant impact on the development of technology.

In materials with low-dimensional structures, such as thin nano-layers of composites based on high-temperature superconductors or superconductor-multiferroic heterostructures, including layered transition metal dichalcogenides, electron–electron and electron–phonon interactions cause the formation of various low-temperature phases and phase transitions, e.g., density waves charge/spin, superconductivity, metal-insulator transition, Peierls instability, structural superstructure, and different magnetic phases. All this makes these materials interesting for theoretical and experimental research, as well as for technological application in cooperation with industries, including Josephson and Andreev junctions, superconducting detectors, and antennas. The impact of destructive mechanisms and factors such as radiation, the aging process of HTS, and superconducting tapes and wires used in superconducting magnets, which are used in the space and medical industries, are also of interest to researchers.

This Special Issue is intended to provide an overview of the progress in selected fields of superconductivity. Emphasis is placed on experimental and theoretical studies of high-temperature superconductors, advances in theoretical understanding, advances in research and applications, as well as the development of new material-synthesis methods.

Dr. Paweł Pęczkowski
Guest Editor

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