Cryogen-free dilution refrigerator system with selected options

我们建议购买一台适合与SQUID磁强计相结合的无制冷剂稀释式制冷机，以研究毫伏开尔文温度下的磁化特性。虽然Squid的工作温度低至1.5K左右是无处不在的，但在野外却没有在较低温度下工作的系统。然而，在拓扑绝缘子的磁性和超导性质方面存在着重大问题，这恰恰需要这样一种仪器来解决。例如，考虑形成新的SI单位制基础的电子量子效应。磁性拓扑绝缘体是一类在这一领域有应用前景的新材料，它允许在没有磁场的情况下实现量子霍尔电阻，表现为量子反常霍尔效应(QAHE)。然而，这些拓扑绝缘体中的铁磁态的性质仍然不清楚。为了了解这种状态，必须在样品表现出QAHE的相同条件下进行测量，目前QAHE远低于1K。因此，一个主要的目标是开发技术来精确地表征QAHE器件的磁性和结构性质，特别是使用可以在30K到10mK的可变温度下工作的SQUID传感器，以高分辨率地表征V掺杂的(Bi，Sb)Te系统，这将使我们能够回答一些关于这种材料中铁磁态的性质的基本物理问题。除了这一主要目的外，MK-SQUID的出现将有利于拓扑超导的研究和我们对磁性TIS的其他研究。该仪器将在这一领域提供独特的功能，并将使我们能够显著推进对这些重要的新材料的理解。

We propose to purchase a cryogen-free dilution refrigerator appropriate for the incorporation of a SQUID magnetometer, for the purpose of studying magnetization properties at millikelvin temperatures. While Squid operating down to about 1.5K are omnipresent, systems working at lower temperatures are absent in the field. There are however significant questions, with regards to magnetic and superconducting properties of Topological insulators which require precisely such an instrument to address. For example, consider the electrical quantum effects that form the basis of the new SI unit system. A promising new material class for applications in this field are the magnetic topological insulators, which allows the quantum Hall resistors to be realized without a magnetic field, in the form of the quantum anomalous Hall effect (QAHE). However, the nature of the ferromagnetic state in these topological insulators is still unclear. To understand this state, it must be measured under the same conditions where the samples exhibit the QAHE, which at present is well below 1K. A major objective is thus to develop techniques to accurately characterize the magnetic and structural properties of the QAHE devices, especially V-doped (Bi,Sb)Te system with high resolution using the SQUID sensor that can work in variable temperatures from 30K down to 10mK, which will allow us to answer some fundamental physics questions on the nature of the ferromagnetic state in this material. In addition to this primary aim, the availability of mK-SQUID will be beneficial to projects on topological superconductivity and to our other investigation on magnetic TIs in general. This instrument will provide a unique functionality in this field, and will allow us to significantly move forward the understanding of these important novel materials.