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For the first time, researchers at the University of Bayreuth and the Karlsruhe Institute of Technology (KIT) have succeeded in applying nuclear magnetic resonance (NMR) spectroscopy in experiments analysing material samples under very high pressure that is similar to the pressure in Earth's lower mantle. The process presented in Science Advances is expected to improve our understanding of elementary particles, which often behave differently under high pressure than they do under normal conditions. It is predicted to encourage technological innovations and also to enable new insights into the earth's interior and the history of the earth, in particular, the conditions for the origins of life.

Diamonds put matter under high pressure

High pressure research in the geosciences and materials science is known for leading to the discovery of some fascinating and completely unexpected phenomena. Under extremely high pressure, materials that are normally nonconductive become superconductors; apparently simple solid state bodies suddenly assume highly complex crystalline structures; the smallest elementary particles such as electrons and protons display unpredictable properties. The University of Bayreuth's Bavarian Research Institute of Experimental Geochemistry & Geophysics (BGI) is one of the world's leading centres for high pressure research. In 2016, a team of researchers at the BGI achieved a pressure of over one terapascal for the first time in their experiments in materials science – that's three times higher than the pressure at the centre of the earth. These pressure levels are generated in extremely small spaces in diamond anvil cells. Using these devices, material samples are placed between the heads of two diamonds which are positioned exactly opposite one another and exert extremely high pressure on the material.

In this way, X-ray crystallography has led to some surprising discoveries about the structures and behaviour of matter again and again. However, NMR spectroscopy - which is utilized, for example, to clarify the structures and interactions of biomolecules - had not yet been used in high pressure research. There was a technical obstacle standing in the way: until now, it was hardly possible for the magnetic fields important for NMR to focus on the tiny samples in the diamond anvil cells and to measure the signals that are thus produced.

Magnetic lenses combined with diamonds

However, in August 2017 scientists at the KIT's Institute of Microstructure Technology published a new method that enables NMR spectroscopy to be used for highly precise experiments in tiny spaces. In doing so, they made relevant enhancements to magnetic lenses known as "Lenz lenses" (named after German physicist Emil Lenz, 1804-1865). "These research findings in Karlsruhe immediately suggested to us here in Bayreuth that Lenz lenses might be installed in the diamond anvil cells to enable NMR experiments at high pressures," reported Prof. Dr. Leonid Dubrovinsky, high pressure researcher in Bayreuth. Together with Dr. Sylvain Petitgirard and Dr. Thomas Meier of BGI, Dubrovinsky got in touch with Prof. Dr. Jan Korvink's team of researchers in Karlsruhe. In just a short time, intensive cooperation enabled the diamonds in the anvil cells to be combined with the Lenz lenses such that the material samples enclosed in the cells could be examined with NMR spectroscopy. In initial experiments, the samples were exposed to pressures of 72 gigapascals (720,000 bars), at the levels in Earth's lower mantle.

New prospects for research and innovation

"The portfolio of X-ray crystallography process that was available to us up to now for high pressure research in the geosciences and materials science has been considerably expanded thanks to the addition of NMR spectroscopy. The possible areas of application cannot even be foreseen yet. We can now study the behaviour of electrons and atomic nuclei in systems that are important in physics and geology with a much higher degree of precision than before," explained Dubrovinsky. "These findings could advance innovative developments, e.g. in energy or medical technology. One day, they may even help us to solve the great riddle of how life arose on Earth," Dubrovinsky said.