Studies of the Andreev Conversion Process and Single-Particle Tunneling in Novel and Unconventional Superconductors

新型和非常规超导体中安德烈耶夫转换过程和单粒子隧道效应的研究

• 批准号: 0706013
• 负责人: Laura Greene
• 金额: $ 36万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-01 至 2011-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0706013&HistoricalAwards=false
• 关键词: Studies; Andreev; Conversion; Process; Single

******NON-TECHNICAL ABSTRACT****Superconductivity, a state characterized by zero resistance (perfect conductivity) and the expulsion of magnetic fields (perfect diamagnetism) was discovered in metals at very low temperatures in 1911. In 1957, the microscopic mechanism for superconductivity was discovered; that the individual electrons in the superconductor form pairs and the underlying lattice of the atoms in the material provided the basis for the electrons to pair, the pairing interaction. Temperatures close to absolute zero were thought to be necessary for metals to become superconducting. In 1986, the "high-temperature superconductors" were discovered, which superconduct at much more easily obtainable temperatures. Not only did applications then become more promising, but these materials represented a new state of matter, yet to be understood. Unlike the conventional superconductors known before 1986, in high-temperature superconductors the pairing interaction depends on the direction that the electron travels in the lattice, so these materials are classified as "unconventional." Heavy-fermion superconductors, discovered just before high-temperature superconductors, are also unconventional, and the electrons within the heavy fermion materials act as if they were very heavy. The mechanism of unconventional superconductivity remains a mystery, so the primary task of this project is to determine, microscopically, why the electrons pair. To help answer this question, investigations of how electrons transport across the interface of an unconventional superconductor with a regular metal will be performed. These studies may lead to the development of superconductors with more practical physical properties and higher transition temperatures and to the potential use superconductors and normal metals together in microelectronics power transmission applications. This project makes extensive use of materials microanalysis techniques and enjoys broad collaborations, so students involved will be well prepared to be successful materials physicists in industry, national laboratories, and universities.******TECHNICAL ABSTRACT****This individual investigator award supports experimental studies of the electronic structure of novel and unconventional superconductors and charge transport across their interfaces. Point-contact Andreev reflection spectroscopy (PCARS) and recently developed tunneling spectroscopic techniques will provide detailed, high-resolution spectroscopic measurements that not only directly probe the superconducting order parameter symmetry, but are also crucial in elucidating the pairing mechanism. The focus of the project is on the heavy-fermion superconductors, particularly the pure and doped CeMIn5 (M=Co,Ir,Rh) series, along with other novel superconductors that exhibit non-magnetic and magnetic ground states. This project is further directed towards a deeper understanding of the fundamentals of the Andreev reflection process between a heavy-fermion superconductor and a normal metal; a process not explained by existing theories. To address this issue, a systematic study of PCARS using superconducting tips will be performed on a range of heavy-fermion normal metals. Students will gain extensive training in materials microanalysis and charge transport. Increased understanding of the basic mechanism and charge transport across the interface of unconventional superconductors will lead to the ability to create superconductors with more practical physical properties and higher transition temperatures, and to potential applications using superconductors and normal metals together in microelectronics power transmission applications.

** 非技术摘要 * 超导性，一种以零电阻（完美导电性）和磁场驱逐（完美抗磁性）为特征的状态，于1911年在极低温度下在金属中发现。 1957年，超导体的微观机制被发现;超导体中的单个电子形成对，材料中原子的基本晶格为电子配对提供了基础，即配对相互作用。 接近绝对零度的温度被认为是金属成为超导体的必要条件。 1986年，人们发现了“高温超导体”，这种超导体在更容易获得的温度下超导。这些材料不仅在应用上变得更有前景，而且还代表了一种新的物质状态，尚待理解。 与1986年以前已知的传统超导体不同，高温超导体中的对相互作用取决于电子在晶格中的运动方向，因此这些材料被归类为“非常规”。“在高温超导体之前发现的重费米子超导体也是非常规的，重费米子材料中的电子表现得好像它们非常重。非常规超导的机制仍然是一个谜，所以这个项目的主要任务是在微观上确定电子配对的原因。 为了帮助回答这个问题，将进行电子如何穿过非常规超导体与常规金属的界面传输的研究。这些研究可能会导致超导体的发展与更实用的物理性能和更高的转变温度和潜在的使用超导体和普通金属一起在微电子电力传输应用。该项目广泛使用材料微分析技术，并享有广泛的合作，因此参与的学生将为成为工业，国家实验室和大学的成功材料物理学家做好充分准备。技术摘要 * 该个人研究者奖支持对新型和非常规超导体的电子结构及其界面电荷传输的实验研究。点接触Andreev反射光谱（PCARS）和最近开发的隧道光谱技术将提供详细的，高分辨率的光谱测量，不仅直接探测超导序参数对称性，但也是至关重要的阐明配对机制。 该项目的重点是重费米子超导体，特别是纯的和掺杂的CeMIn 5（M=Co，Ir，Rh）系列，沿着其他新型超导体，表现出非磁性和磁性基态。 该项目进一步旨在更深入地了解重费米子超导体和正常金属之间的Andreev反射过程的基本原理;现有理论无法解释这一过程。 为了解决这个问题，系统的研究PCARS使用超导尖端将进行一系列重费米子正常金属。 学生将获得材料微观分析和电荷传输方面的广泛培训。 对非常规超导体的基本机制和电荷输运的理解的增加将导致创造具有更实用的物理性质和更高的转变温度的超导体的能力，以及在微电子电力传输应用中一起使用超导体和普通金属的潜在应用。