3He cryostat for low energy beta-NMR

在两种材料之间的界面附近，材料的所有电子、磁性和结构特性都是不同的。在某些情况下，这些变化是微妙的，仅限于几个原子层，而在其他情况下，这些变化是巨大的，延伸到许多纳米。一般来说，单个界面（或多层界面中的一系列界面）具有其独特的性质和相，这些性质和相具有重要的技术意义。磁性多层膜的巨磁阻是2007年诺贝尔物理学奖的一个著名例子。了解界面物理的进展是缓慢的，因为很少有实验方法能够以深度分辨的方式探测局部性质。最近，申请人为此目的开发了一种低能β探测核磁共振的新技术。主要思想是使用一个可变的低能量的高自旋极化放射性原子核束，如8Li，来探测纳米长度尺度上的局部性质。由于核极化是通过探测核的不对称β衰变来检测的，因此该技术的灵敏度比传统的核磁共振大约高10个数量级。我们正在申请资金，用于研制3He泵浦低温恒温器，在绝对零度以上0.35度的温度下探索物质的量子相及其界面。

All electronic, magnetic and structural properties of a material are different near an interface between two materials.  In some cases these changes are subtle and confined to just a few atomic layers while in others the changes are dramatic and extend over many nanometres. In general a single interface (or series of interfaces in a multilayer) has its own distinct properties and phases which are of great technological significance. Giant magnetoresistance of magnetic multilayers is one notable example which lead to the 2007 Nobel Prize in Physics. Progress in understanding physics at interfaces is slow since few experimental methods are capable of probing local properties in a depth resolved manner. Recently the applicants have developed a novel technique of low energy beta-detected nuclear magnetic resonance for this purpose. The main idea is to use a variable low energy beam of highly spin-polarized radioactive nuclei such as 8Li to probe the local properties on a nm length scale. Since the nuclear polarization is detected through the asymmetric beta-decay of the probe nucleus, the technique is roughly ten orders of magnitude more sensitive than conventional NMR. We are requesting funds here for a pumped 3He cryostat to explore quantum phases of matter and their interfaces at temperatures down to  0.35 degrees above absolute zero.