Acquisition of a Dilution Refrigerator and Superconducting Magnet System

配套资金用于购置和建设一个独特的设施，用于研究超低温磁场下的超导薄膜和结构。该仪器包括一个高冷却功率稀释制冷机，能够达到低于5 mlikelvin的温度，一个7特斯拉水平/8.5特斯拉垂直矢量磁铁系统，以及冰箱和磁铁系统运行所需的相关泵，电源和气体处理系统。由于许多研究涉及到在低温下沉积在基底上制备薄膜的研究，因此该设备将被安装在现有的超高真空生长室中。这将以一种允许在冷基板上原位沉积薄膜的方式完成，但也保留了冰箱和磁铁独立操作的选择。资金还用于购买一个核取向温度计，作为主要的温度标准，以及一个直流SQUID系统，该系统将配置为电压测量模式，以测量极低电流激励下的输运特性。该设备将用于在高磁场（7至14特斯拉）至超低温（低于0.005开尔文）下扩展超导薄膜和结构特性的测量。该设施将用于在超低温和二维极限下研究选定电子系统的量子特性。对于这样的系统，在适当的条件下，量子涨落比热涨落更重要，并且许多系统表现出量子相变而不是热相变。特别感兴趣的是超薄薄膜和结阵列中的绝缘体到超导体的转变，超导体中漩涡的宏观量子隧穿，以及超导体降低转变温度的临界场。这些研究在开发和表征具有重要技术意义的新材料方面具有重要意义和应用。

Matching funds are provided for the acquisition and the construction of a unique facility for the study of superconducting films and structures in magnetic fields at ultralow temperatures. The instrument consists of a high cooling power dilution refrigerator, capable of achieving temperatures below 5 millikelvin, a 7-tesla horizontal/8.5- tesla vertical vector magnet system, and associated pumps, power supplies, and gas handling system needed for the operation of the refrigerator and magnet system. Since many of the investigations involve the study of films prepared by deposition onto substrates held at low temperatures, the equipment will be built into an existing ultrahigh vacuum growth chamber. This will be done in a manner which permits insitu deposition of films onto cold substrates, but which also retains the option of free-standing operation of the refrigerator and magnet. Funds also are provided for the purchases of a nuclear orientation thermometer which will serve as a primary temperature standard, and a dc SQUID system which will be configured in a voltage-measuring mode to gauge transport properties at very low current excitations. The equipment would be used to extend the measurement of properties of superconducting films and structures in high magnetic fields (7 to 14 tesla) to ultralow temperatures (below 0.005 kelvin). The facility would be used to investigate the quantum properties of selected electronic systems in the limits of ultralow temperatures and two dimensions. For such systems, under appropriate conditions, quantum fluctuations are more important than thermal fluctuations, and many systems exhibit quantal rather than thermal phase transitions. The particular interests are in insulator-to-superconductor transitions in both ultrathin films and junction arrays, the macroscopic quantum tunneling of vortices in superconductors, and the critical fields of reduced transition temperature superconductors. These studies have important implicati ons and applications in developing and characterizing new technologically significant materials.