Chalcogenides Superconductors: Nonconventional Superconductivity in New Phases

超导性是一种量子现象，在临界温度以下，电阻完全消失。100多年前发现的传统超导体是由简单的金属组成的，大约50年前就完全解释了这一现象。超导体的应用包括在相同的温度和横截面积下传输比金属多许多倍的功率的能力。然而，传统超导体的局限性在于它们必须被冷却到非常低的温度。更重要的是，它们在外部磁场（临界场）中可以传输的电流（临界电流）的大小受到限制。多年来，传统超导体得到了改进，并发现了新的领域，增强了磁场中的载流能力，使高场研究磁体和包括MRI（磁共振成像）在内的应用成为可能。进入大约40年前发现的非常规超导体，随后是30年前发现的高温超导体，这些材料在临界温度以上就不是好金属了，还没有完全被理解，但这些有趣的材料中有许多可以在极高的磁场中传输比传统超导体更多的电流。非常规超导体的应用不仅可以是变革性的，而且解释其正常和超导性质的基础物理学在这段时间里仍然难以捉摸。在固态和材料化学计划的支持下，研究小组将研究非常规超导相，包括铌和钽等金属，以及非金属元素硫，硒或碲。过渡金属硫属化物包括具有高临界温度的超导相，例如铁和钼的硫属化物。研究工作的重点是新的三元和四元铌和钽硫属化物，其中一些相显示出非常大的临界场的非常规超导性。这种行为的核心是电子电荷、电子自旋和晶格（晶体结构）之间的相互作用。至关重要的是高质量样品的合成和生长，以详细了解结构-性质关系。使用衍射技术的结构表征将与物理性质的研究相结合，包括磁化率，电子传输性质和光学性质。此外，调谐的物理性质的化学取代和化学计量变化的组合进行了探讨。这些阶段的晶体生长与美国国家科学院报告“晶体物质前沿：从发现到技术”中所描述的领域非常匹配，该报告侧重于美国发现和生长晶体物质的机会。这项研究是一项高度跨学科的活动，需要各种技能。在本科生，研究生和研究生阶段对学生进行晶体生长和材料表征的艺术和科学培训，培养活跃在这一领域的下一代科学家和工程师，并建立应对未来挑战所需的高技能劳动力。

Non-Technical AbstractSuperconductivity is a quantum phenomenon in which, below a critical temperature, the electrical resistance completely vanishes. Conventional superconductors, discovered over 100 years ago, are composed of simple metals, and the phenomenon was completely explained about 50 years ago. The applications of superconductors include the ability to transmit many times more power than metals at the same temperature and cross-sectional area. However, conventional superconductors are limited in that they have to be cooled to very low temperatures. More importantly, they are limited in the magnitude of current they can transmit (critical current) in an external magnetic field (critical field). Over the years, conventional superconductors have been improved and new areas have been discovered that enhanced these current carrying capabilities in a magnetic field, making possible high-field research magnets and applications that include MRI (Magnetic Resonance Imaging). Enter the discoveries of unconventional superconductors about 40 years ago, followed by the discovery of high-temperature superconductors 30 years ago, these materials which are not good metals above their critical temperature, are not completely understood, but many of these intriguing materials can transmit much more current in extremely high magnetic fields than conventional superconductors. Not only can the applications of unconventional superconductors be transformative, but the fundamental physics explaining their normal and superconducting properties remains elusive over all of this time. With the support of the Solid State and Materials Chemistry program, the research group will study unconventional superconductor phases that include metals such as niobium and tantalum, as well as the nonmetallic elements sulfur, selenium or tellurium. Technical AbstractTransition metal chalcogenides comprise superconducting phases with high critical temperatures, such as iron and molybdenum chalcogenides. The research effort focuses on new ternary and quaternary niobium and tantalum chalcogenides, with some of these phases showing unconventional superconductivity with very large critical fields. At the core of this behavior are interactions between electron charge, electron spin and the lattice (the crystal structure). Critically important are the synthesis and growth of high quality samples for a detailed understanding of structure-property relationships. Structural characterization using diffraction techniques will be combined with investigations of physical properties, including magnetic susceptibility, electronic transport properties and optical properties. Furthermore, tuning of the physical properties by a combination of chemical substitutions and stoichiometry variations are explored. Crystal growth of such phases is well matched to the areas delineated in the National Academy of Sciences report "Frontiers in Crystalline Matter: From Discovery to Technology," which focuses on the opportunities for discovery and growth of crystalline matter in the US. This research is a highly interdisciplinary activity that requires a variety of skills. Training of students in the art and science of crystal growth and characterization of materials at undergraduate, graduate and postgraduate levels trains the next generation of scientists and engineers active in this field and builds the highly skilled workforce needed to address tomorrow's challenges.