Superstructures, Miscibility Gaps and Superconductivity in Two-Band Electronic Systems

双波段电子系统中的超结构、混溶间隙和超导性

• 批准号: 2219906
• 负责人: Theo Siegrist
• 金额: $ 49.47万
• 依托单位: Florida State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2219906&HistoricalAwards=false
• 关键词: Superstructures; Miscibility; Gaps; Superconductivity; Two

Non-Technical SummarySuperconductivity, where a material loses its resistivity, is an interesting and technologically important phenomenon. For instance, medical diagnostic systems, MRIs, use superconductors to generate the high magnetic fields needed, and power transmission lines may use superconductors to transmit electrical power without losses. However, superconductors are sensitive to magnetic fields, with superconductivity suppressed if the magnetic field exceeds a material specific threshold. This threshold is usually related to the temperature where a material becomes superconducting, and represents an upper limit. Research into materials that substantially exceed this limit indicates that the superconductivity in this class of materials may be due to different effects than in the classic systems. This project, supported by the Solid State and Materials Chemistry Program in NSF’s Division of Materials Research, will allow researchers at Florida State University to explore possible origins of this effect, and is expected to provide insights into ways of improving the performance of superconductors. A material consisting of niobium, palladium and sulfur or selenium is the focus of this research, where its crystal structure and electrical resistivity depends on the palladium content, and the magnetic field threshold exceeds the expected value more than four-fold, making this compound well suited to study this effect. In this particular compound, the electrons carrying the current experience additional interactions that affect the superconductivity, and thus, the magnetic field threshold. This research further develops the work force for tomorrow’s technology needs, and advances the understanding of exotic superconductivity. It combines the discovery and growth of materials with novel structural features with an in-depth characterization of their properties, an interdisciplinary activity that requires a variety of skills that are applicable in many fields. Training students in the art and science of crystal growth and characterization of materials at undergraduate, graduate and postgraduate levels is instrumental to the next generation of scientists and engineers that will be active in this field. Technical SummaryUnconventional multi-band superconductivity has been observed in ternary niobium-palladium and tantalum-palladium chalcogenides, phases with variable palladium stoichiometry. The interactions between charge, spin and lattice are at the core of these effects, giving rise to unconventional physical behavior. This project, supported by the NSF’s Division of Materials Research, focuses on the interplay of intercalation, miscibility gaps, structural order, superstructure formation, and electronic behavior in Nb2PdxX5 (X=chalcogen) and related systems, where the palladium atoms can be considered the intercalating atoms. Superconductivity in these phases is associated with a record high ratio of the upper critical field Hc2 to the superconducting transition temperature Tc. In these systems, the palladium atoms order in long-range incommensurate superstructures for different palladium content, and induce miscibility gaps, where certain palladium concentrations are not found. The superconductivity is linked to the Pd stoichiometry and the development of these superstructures, where the derived superconducting coherence length is of the same order as the superstructure periodicity, suggesting an intimate coupling of the two effects. Single crystals of Nb2PdxX5 will be grown and characterized using X-ray diffraction to investigate the details of the superstructures, and their correlation with the superconducting transition temperature and the upper critical field Hc2. NSF supported National Facilities are crucial to this research, where X-ray diffraction at synchrotron sources and high magnetic field measurements will be carried out.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术概述超导性，即材料失去其电阻率，是一种有趣的和技术上重要的现象。例如，医疗诊断系统MRI使用超导体来产生所需的高磁场，并且电力传输线可以使用超导体来无损耗地传输电力。然而，超导体对磁场敏感，如果磁场超过材料特定的阈值，超导性就会受到抑制。该阈值通常与材料变为超导的温度有关，并且代表上限。对大大超过这个极限的材料的研究表明，这类材料的超导性可能是由于与经典系统不同的效应。该项目由NSF材料研究部的固态和材料化学计划支持，将使佛罗里达州立大学的研究人员能够探索这种效应的可能起源，并有望为提高超导体性能的方法提供见解。由铌、钯和硫或硒组成的材料是这项研究的重点，其晶体结构和电阻率取决于钯含量，磁场阈值超过预期值四倍以上，使这种化合物非常适合研究这种效应。在这种特殊的化合物中，携带电流的电子经历了额外的相互作用，影响了超导性，从而影响了磁场阈值。 这项研究进一步发展了未来技术需求的工作力量，并推进了对奇异超导性的理解。它结合了材料的发现和生长，具有新颖的结构特征，并对其特性进行了深入的表征，这是一项跨学科的活动，需要各种适用于许多领域的技能。在本科生，研究生和研究生水平的晶体生长和材料表征的艺术和科学培训学生是有助于下一代的科学家和工程师，将活跃在这一领域。在具有可变钯化学计量比的三元铱-钯和钽-钯硫属化物中观察到了非常规的多带超导性。电荷、自旋和晶格之间的相互作用是这些效应的核心，导致了非常规的物理行为。该项目由美国国家科学基金会材料研究部支持，重点研究Nb 2 PdxX 5（X=硫属元素）和相关系统中插层，可伸缩间隙，结构有序，超结构形成和电子行为的相互作用，其中钯原子可以被认为是插层原子。在这些阶段中的超导性与上临界场Hc 2与超导转变温度Tc的创纪录的高比率相关联。在这些系统中，对于不同的钯含量，钯原子在长程不相称的超结构中有序，并产生混溶间隙，其中没有发现某些钯浓度。超导电性与钯化学计量和这些超结构的发展有关，其中推导出的超导相干长度与超结构周期性具有相同的数量级，表明这两种效应密切耦合。Nb 2 PdxX 5单晶将生长和使用X射线衍射的特征，以调查的超结构的细节，以及它们与超导转变温度和上临界场Hc 2的相关性。美国国家科学基金会支持的国家设施对这项研究至关重要，在同步加速器源和高磁场测量的X射线衍射将进行。这个奖项反映了美国国家科学基金会的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。