He^3 Cryostat for Muon Spin Rotation/Relaxation Studies of Quantum Materials

用于量子材料 Mu 子自旋旋转/弛豫研究的 He^3 低温恒温器

• 批准号: RTI-2021-00680
• 负责人: Luke, Graeme
• 金额: $ 6.44万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Research Tools and Instruments
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=718000
• 关键词: He; Cryostat; Muon; Spin; Rotation

Conventional phase transitions between an ordered and disordered state are driven by thermal fluctuations. A profoundly different kind of transition can occur in strongly-correlated electronic materials characterized by competing phases. When one of the phase transition temperatures is driven to absolute zero by a non-thermal control parameter (applied pressure, applied magnetic field or chemical manipulation of electron density), a quantum critical point (QCP) separating two distinct quantum phases of matter may occur. Near a QCP unusual phenomena can emerge (e.g. high-temperature superconductivity, non-Fermi liquid behaviour, partial order at the verge of magnetism) and quantum fluctuations can affect the properties of a material to remarkably high temperatures. Understanding quantum criticality constitutes a grand challenge of modern condensed matter physics. In many cases the occurrence of a QCP may be circumvented by disorder (extrinsically or intrinsically driven) that produces phase separation in the critical region. Local experimental probes are required to recognize and characterize phase separation. The muon spin rotation/relaxation (uSR) technique is such a probe. This method is based on the implantation of spin-polarized positive muons in a material and the subsequent detection of the decay positrons to reveal the influence of the local magnetic fields on the motion of the muon spin. As a pure magnetic probe, the uSR method is sensitive to various kinds of magnetism and is sensitive to spatially segregated phases. The Centre for Molecular and Materials Science (CMMS) at TRIUMF is home to a unique SR spectrometer, called “NuTime”, which provides a means of probing materials subject to a high magnetic field. Its applicability to the study of quantum materials is currently limited by temperature. It is proposed, that by outfitting NuTime with a He-3 cryostat to cool materials to sub-Kelvin temperatures, Canadian and International researchers can apply uSR to the study of quantum criticality and novel states of matter tunable by applying magnetic field. The proposed equipment will establish a unique capability in the Western Hemisphere for quantum materials' research, a recognized strategic priority research area in Canada. A successful RTI application (2016 Award) supported the development and purchase of a He-3 cryostat. However, the time for this development meant that only 40% of the purchase price was expended before NSERC required the return of the remainder of the purchase price. The development is now complete and the system is being manufactured. This proposal is to fund the remainder of the purchase price, to allow the delivery of the system and is to replace funds returned to NSERC in 2020.

有序态和无序态之间的传统相变是由热波动驱动的。在以竞争相为特征的强相关电子材料中，可能发生一种截然不同的转变。当其中一个相变温度被非热控制参数（施加压力、施加磁场或电子密度的化学操作）驱动到绝对零度时，可能会出现一个量子临界点（QCP），将物质的两个不同的量子相分开。在QCP附近可以出现不寻常的现象（例如高温超导，非费米液体行为，磁性边缘的偏序），量子涨落可以影响材料的性质到非常高的温度。