High-Sensitivity Nuclear Magnetic Resonance at Giga-Pascal Pressures: A New Tool for Probing Electronic and Chemical Properties of Condensed Matter under Extreme Conditions

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

Since Percy Bridgman's hallmark experiments of condensed matter under high hydrostatic pressures at the beginning of the last century, the field of high pressure physics has evolved rapidly¹. A large number of intriguing phenomena are known to occur under pressures of several GPa². In addition, the response of condensed matter systems to high pressure has taught us a lot about their electronic ground and excited states^3,4.

Unfortunately, techniques for the investigation of the electronic properties of condensed matter at Giga-Pascal pressures are rare, with x-ray or DC resistance measurements leading the....

Protocol

1. Mounting and Aligning of the 6H-SiC Large Cone Boehler-type Anvils

1. Fix the piston and x-y plate in the mounting tools and insert the Boehler-type anvils in the seating area.
2. Make sure each anvil sits firmly in the backing plates.
3. Using epoxy resin, (e.g., Stycast 1266), glue both anvils to their seats. Cure for 12 h at RT, or 65 ºC in a furnace for 2 hr.
4. For a sufficient anvil alignment, use the M1 set-screws to align the backing plates and monitor the parallelism of both anvils. If the anvils were found to be non-parallel, remove the epoxy resin and restart at point 1.2.

2. Ga....

Results

Figure 3 shows how the completely assembled pressure cell, the wiring, and the mounting onto a typical NMR probe look like. In the following, several experiments will be reviewed which should enable the reader to gather a broad overview about the benefits and limits of the introduced technique.

Figure 1. Various Approaches for high pressure NMR: (A.......

Discussion

A new and promising method to perform NMR at Giga-Pascal pressures was described. This method opens up the door to a broad variety of NMR experiments due to its excellent sensitivity and resolution. Nevertheless, several steps described in the protocol section are crucial to the outcome of the experiment. Especially, the preparation of the micro-coil and its fixation in the Cu-Be gasket is very difficult and requires some experience. In the following, some important tips are given, which should help a first successful ap.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
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