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

有序和无序状态之间的常规相变是由热波动驱动的。在强相关的电子材料中，一种截然不同的转变可能发生在竞争相的特征中。当其中一个相变温度被非热控制参数（施加的压力、施加的磁场或电子密度的化学操纵）驱动到绝对零度时，可能会出现分离物质的两个不同量子相的量子临界点（QCP）。在QCP附近可能会出现不寻常的现象（例如高温超导性，非费米液体行为，磁性边缘的部分有序性），量子涨落可能会影响材料的性质，达到非常高的温度。 理解量子临界性是现代凝聚态物理学的一个重大挑战。在许多情况下，QCP的发生可以通过在临界区产生相分离的无序（外在或内在驱动）来避免。需要本地实验探针来识别和表征相分离。μ子自旋旋转/弛豫（uSR）技术就是这样一种探测器。这种方法是基于自旋极化的正μ子在材料中的注入和随后的衰变正电子的检测，以揭示局部磁场对μ子自旋运动的影响。作为一种纯磁探针，uSR方法对各种磁性敏感，对空间分离相敏感。 TRIUMF的分子和材料科学中心（CMMS）拥有一台独特的SR光谱仪，称为“NuTime”，它提供了一种探测高磁场材料的方法。它在量子材料研究中的适用性目前受到温度的限制。有人建议，通过配备NuTime与He-3低温恒温器将材料冷却到亚开尔文温度，加拿大和国际研究人员可以将uSR应用于量子临界性和通过施加磁场可调的物质新状态的研究。拟议的设备将在西半球建立一个独特的量子材料研究能力，这是加拿大公认的战略优先研究领域。 一项成功的RTI应用（2016年奖）支持了He-3低温恒温器的开发和购买。 然而，这一发展的时间意味着只有40%的购买价格之前，NSERC要求返回购买价格的其余部分。 目前开发工作已经完成，系统正在制造中。 该提案将为购买价格的剩余部分提供资金，以允许系统的交付，并将取代2020年返还给NSERC的资金。

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.