Development of Wideband Scanning Superconducting Quantum Interference Device Susceptometers for Nanomagnetic Materials Research and Education

用于纳米磁性材料研究和教育的宽带扫描超导量子干涉装置磁感受计的开发

• 批准号: 0216470
• 负责人: Martin Huber
• 金额: $ 22万
• 依托单位: University of Colorado at Denver-Downtown Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-15 至 2006-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0216470&HistoricalAwards=false
• 关键词: Development; Wideband; Scanning; Superconducting; Quantum

Nanomagnetic devices for applications such as quantum computing and high-capacity memory cannot be developed without faster, more sensitive characterization tools to directly probe phenomena and material structures at the nanoscale. The objective of this work is to advance the capability of a non-invasive, high-sensitivity technique, scanning superconducting quantum interference device (SQUID) susceptometry, for the dynamic characterization of nanomagnetic materials, systems, and phenomena. The principal investigator achieves this objective through two innovations. First, spin sensitivity is improved from the current state of the art, a few thousand electron spins per Hz1/2 , to a few tens of spins per Hz1/2. This improvement is accomplished by reduction of pickup loop dimensions in a combined optical and electron-beam lithography process and by utilizing an ultra-low-noise dc SQUID process. Second, bandwidth is increased from the current state of the art, tens of kHz, to tens of MHz by the use of dc SQUID series array amplifiers as preamplifiers for the dc SQUID susceptometer. The devices are characterized for flux sensitivity and bandwidth at 300 mK and 20 mK. Operation at 300 mK is necessary for the e-beam defined Al pick-up loops to become superconducting, and operation at 20 mK is essential for the study of quantum decoherence mechanisms in electronic systems. Undergraduates, working with graduate students in the collaborator's laboratory, characterize the spin sensitivity of the devices and their performance under realistic scanning conditions by imaging individual cobalt nanomagnetic spheres of controlled diameters ranging from 3 nm to 10 nm and magnetic moments ranging from tens to tens of thousands of electron spins. Further, one SQUID susceptometer is used to image a second, identical device to quantitatively characterize the noise generated by the devices. The scientific emphasis of this project is to produce sensors that have applications in the area of nanoscale structures, novel phenomena, and quantum control and to use these sensors to image both static and dynamic properties of individual cobalt nanomagnets. Integration of a high-sensitivity, high-bandwidth SQUID susceptometer into a scanning platform significantly increases the number and kind of systems that can be studied, decreases the turn-around time, and increases the number of samples that can be studied in a single experiment. Thus, this project contributes to advances in nanoscale materials, devices and system architecture. An added benefit of this project is the educational benefits at both CU-Denver (PI's institution) and Stanford University (collaborator's institution) resulting from the collaboration between CU-Denver undergraduate students and Stanford graduate students.

如果没有更快、更灵敏的表征工具来直接探测纳米尺度的现象和材料结构，就无法开发用于量子计算和大容量存储器等应用的纳米磁性设备。这项工作的目的是提高一种非侵入性的、高灵敏度的技术--扫描超导量子干涉装置(SQUID)磁感度测量的能力，以动态表征纳米磁性材料、系统和现象。首席研究员通过两项创新实现了这一目标。首先，自旋灵敏度从当前技术水平的每Hz1/2几千个电子自旋提高到每Hz1/2几十个自旋。这一改进是通过减少光学和电子束组合光刻工艺中的拾取回路尺寸和利用超低噪声DC Squid工艺实现的。其次，通过使用DC Squid系列阵列放大器作为DC Squid磁感计的前置放大器，带宽从当前技术水平的数十kHz增加到数十MHz。器件的磁通灵敏度和带宽分别为300mK和20mK。电子束定义的Al拾取回路在300mK下工作是超导所必需的，而在20mK下工作是研究电子系统中量子退相干机制的关键。本科生与研究生在合作者的实验室中合作，通过对直径从3 nm到10 nm的单个钴纳米磁球成像，以及从数万到数万个电子自旋的磁矩，来表征设备的自旋敏感度及其在现实扫描条件下的性能。此外，一个鱿鱼感受器被用来对第二个相同的设备进行成像，以定量地表征这些设备所产生的噪声。该项目的科学重点是制造在纳米结构、新现象和量子控制领域有应用的传感器，并使用这些传感器来成像单个钴纳米磁铁的静态和动态特性。将高灵敏度、高带宽的SQUID敏感仪集成到扫描平台中，显著增加了可以研究的系统的数量和种类，缩短了周转时间，并增加了在单个实验中可以研究的样本数量。因此，该项目有助于纳米材料、器件和系统架构的进步。该项目的另一个好处是，科罗拉多大学丹佛分校(派的机构)和斯坦福大学(合作者的机构)都从科大-丹佛本科生和斯坦福研究生之间的合作中获得了教育方面的好处。