高灵敏度核磁共振的千兆帕斯卡压力：一种新的工具，用于极端条件下探测电子和化工凝聚态的性质
Summary
Nuclear magnetic resonance is one of the most important spectroscopic tools. Here, the development of a new approach under high pressure, currently up to 10.1 GPa, is presented. This opens a new window into condensed matter physics and chemistry, where high-pressure research is of great importance.
Abstract
Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their electronic properties. The application of high pressure enables one to synthesize new materials, but the response of known materials to high pressure is a very useful tool for studying their electronic structure and developing theories. For example, high-pressure synthesis might be at the origin of life; and understanding the behavior of small molecules under extreme pressure will tell us more about fundamental processes in our universe. It is no wonder that there has always been great interest in having NMR available at high pressures. Unfortunately, the desired pressures are often well into the Giga-Pascal (GPa) range and require special anvil cell devices where only very small, secluded volumes are available. This has restricted the use of NMR almost entirely in the past, and only recently, a new approach to high-sensitivity GPa NMR, which has a resonating micro-coil inside the sample chamber, was put forward. This approach enables us to achieve high sensitivity with experiments that bring the power of NMR to Giga-Pascal pressure condensed matter research. First applications, the detection of a topological electronic transition in ordinary aluminum metal and the closing of the pseudo-gap in high-temperature superconductivity, show the power of such an approach. Meanwhile, the range of achievable pressures was increased tremendously with a new generation of anvil cells (up to 10.1 GPa), that fit standard-bore NMR magnets. This approach might become a new, important tool for the investigation of many condensed matter systems, in chemistry, geochemistry, and in physics, since we can now watch structural changes with the eyes of a very versatile probe.
Introduction
由于在上个世纪初高静水压力凝聚态珀西·布里奇曼的标志性实验，高压物理学领域已经发展迅速1。大量的有趣的现象是已知的下几个GPA 2的压力下发生。此外，凝聚态系统的高压反应已经告诉我们很多关于他们的电子基态和激发态3,4。
不幸的是，技术的凝聚态的千兆帕斯卡压力的电子性质的研究并不多见，与X射线或直流电阻测量一路领先5。特别地，电子或核磁矩与电子自旋（ESR）或核磁共振（NMR）实验中，检测被绑定到几乎不可能在一个典型的高压砧座单元，其中一个需要从检索的信号来实现一个小v通过砧座和密封垫圈olume供奉。
几个小组已尝试通过使用复杂的安排，要解决这个问题，例如，两个分割线对射频（RF）线圈沿砧块6的侧面缠绕;单或双环流发针谐振器7,8; 。甚至分裂铼垫圈作为RF拾取线圈9， 见图1不幸的是，这些方法仍然从低信号对噪声比（SNR）遭遇，限制了实验应用到大– γ核如1 H 10。有兴趣的读者可以称作其它高压谐振电路实验11 – 15。 Pravica和Silvera 16报告后的核磁共振砧细胞与12.8 GPA，谁研究了邻对位氢转换的最高压力。
随着应用核磁共振极大的兴趣研究量子固体的性质，我们集团很感兴趣，有核磁共振可在高压下，也是如此。最后，在2009年它可以证实高灵敏度砧细胞NMR的确是可能的，如果谐振无线电频率（RF）微线圈是在高压腔包围的样品17直接放置。在这样的方法中，NMR灵敏度是由几个数量级的（主要是由于急剧增加填充的RF线圈的因子），其变得更加具有挑战性NMR实验可能的， 例如在粉末样品的提高，17 O NMR高温超导体在长达7 GPA 18。超导这些材料可以通过施加压力大大放大了，现在就可以按照这个过程与当地的电子探头，承诺根本的洞察管理流程。另一实例为核磁共振高压下的功率从出现什么是believ编为常规参考实验：为了测试引入新砧细胞核磁共振，最著名的材料中的一种测定 – 简单的铝金属。随着压力的增加，从人们所期望的自由电子系统的NMR位移的一个意想不到的偏差被发现。增加下压力的反复实验，也表明新的结果确实是可靠的。最后，与带结构的计算然后将其发现的结果是，铝的费米表面，而无法通过计算年前被检测到的拓扑过渡的表现形式，在计算能力低。的调查结果的环境条件推断表明，这种金属的使用几乎无处不在的特性是由这个特殊的电子状态的影响。
为了追求许多不同的应用的特殊设计的砧座单元（前细胞已经从Cavend进口ISH实验室改造核磁共振）已经制定出来。目前，所使用自制的底盘是能够使用对800微米的底尖刻6H-SiC的砧块到达压力高至25京帕。核磁共振实验，成功地进行了高达10.1 GPa时为止。这种新的细胞的NMR性能被证明是优良19。其主要成分是钛铝（6）-Vanadium（4）与超低间隙水平（等级23），提供约800屈服强度MPa 20。由于它的非磁特性（磁化率χ是约5ppm）它是用于在砧座单元机架的适当材料。引入细胞（ 见图2中的所有自制的压腔设计概述）的整体尺寸小到足以放入普通标准孔核磁共振磁体。最小的设计中，LAC-TM1，这是只有20毫米高和17毫米的直径，也符合典型的小，冷孔磁铁（30毫米孔直径）。第lAC-TM2，这是最新的底盘作者设计，使用四个M4内六角沉头螺栓（做出来的相同的合金作为电池机箱）作为压力驱动机构，允许在内部压力的平稳控制（安装在蓝图补充部分）。
通常情况下，金刚石砧使用，以便产生上述为100GPa最高压力。许茂和21 – 23已经证明，莫桑石砧提供高压的研究具有成本效益的替代方案，高达约60 GPA的压力。因此，碳硅石砧块被用于引入GPA NMR方法。最好的结果是用自Charles＆科尔瓦德的砧座部定制大锥6H-SiC的砧块。与这些细胞中，压力达10.1 GPa时使用800微米的底尖刻砧被发现导致非常好的NMR灵敏度。为了进行比较，李等人报道的1 SNR核为1 H NM自来水中的R，而引入微线圈的方法的SNR显示出25的值对于其体积的七分之一，即使在稍微较低的磁场。
有了这项新措施，以高灵敏度压腔核磁共振可以追求的承诺令人兴奋的新洞察现代材料的物理和化学多种应用。然而，一如既往的灵敏度和分辨率最终限制NMR的应用，特别是，如果一个人的爱好有高得多的压力需要小型的底尖大小。然后，人们不仅以优化电池设计具有更小的RF线圈，而且还考虑增加核极化方法。
Protocol
Representative Results
Discussion
一个新的，有前途的方法，以千兆帕斯卡的压力进行核磁共振被描述。这种方法开启了大门，各种各样的NMR实验，由于其出色的灵敏度和分辨率。然而，在该协议部分中所述的几个步骤是至关重要的实验的结果。特别是，在制备微线圈和其在所述Cu-成为垫圈固定是非常困难的，并且需要一定的经验。在下文中，一些重要的提示被给出，这将有助于该技术的第一次成功应用。
<p class="jove_conte…Divulgazioni
The authors have nothing to disclose.
Acknowledgements
This research was funded by the International Research Training Group (IRTG) “Diffusion in porous Materials”. We acknowledge the technical support from Gert Klotzsche and stimulating discussions with Steven Reichhardt, Thomas Meissner, Damian Rybicki, Tobias Herzig, Natalya Georgieva, Jonas Kohlrautz, and Michael Jurkutat.
Materials
| Name of Material/ Equipment | Company | Catalog Number | Comments/Description |
| Titanium grade 23 | robemetall GmbH | ASTM F 136 | |
| Beryllium copper foil | GoodFellow | CU070501 | Alloy 25 (C17200) |
| Copper wire for micro-coil | Polyfil | — | quote on inquiry |
| Stycast 1266 | Sil-Mid Ldt. | S1266001KG | |
| Moissanite anvils | Charles & Colvard | — | quote on inquiry |
| Paraffin oil (pressure medium) | Sigma Aldrich | 18512-1L | |
| M4 Allen contersunk screws (Ti64) | Der Schraubenladen | DIN912 M4x20 | |
| Optiprexx PLS | Almax-easylab | — | quote on inquiry |
| Ruby spheres (~10-50 µm) | DiamondAnvils.com | P00996 | |
| Manual Toggle Press | DiamondAnvils.com | A87000 | |
| Gasket Thickness Micrometer | DiamondAnvils.com | A86000 | |
| Titanium Scalpel | Newmatic Medical | NM45200710421 | |
| Glass-writing Diamond | Plano | 54467 | |
| Smoothing Awls | Flume | 1 4444 001 | |
| Chuck-jaws (4 jaws) | Flume | 4 561 289 | |
| Lathe | Flume | 4 560 023 | |
| Drilling Machine | Flume | 4 570 020 | |
| Drill chuck | Flume | 4 570 021 | |
| XY stage | Flume | 4 570 022 | |
| Drills (0.30 to 0.50 mm) | Flume | 4 572 652 – 654 | |
| Low Temperature Varnish | SCBshop | SCBltv03 |
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