Scientists use pressure to make liquid magnetism breakthrough

Artist’s rendering of electron spins frustrated as the sample of magnetic material is pressurized into a spin liquid state (Image by Daniel Haskel)

Using two flat-top diamonds and a lot of pressure, scientists have forced a magnetic crystal into a spin liquid state, which may lead to insights into high-temperature superconductivity and quantum computing, reports Argonne National Laboratory.

It sounds like a riddle: What do you get if you take two small diamonds, put a small magnetic crystal between them and squeeze them together very slowly?

The answer is a magnetic liquid, which seems counterintuitive. Liquids become solids under pressure, but not generally the other way around. But this unusual pivotal discovery, unveiled by a team of researchers working at the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility at DOE’s Argonne National Laboratory, may provide scientists with new insight into high-temperature superconductivity and quantum computing.

Though scientists and engineers have been making use of superconducting materials for decades, the exact process by which high-temperature superconductors conduct electricity without resistance remains a quantum mechanical mystery. The telltale signs of a superconductor are a loss of resistance and a loss of magnetism. High-temperature superconductors can operate at temperatures above those of liquid nitrogen (−320 degrees Fahrenheit), making them attractive for lossless transmission lines in power grids and other applications in the energy sector.

But no one really knows how high-temperature superconductors achieve this state. This knowledge is needed to increase these materials’ operating temperature towards ambient temperature, something that would be required for full-scale implementation of superconductors in energy-conserving power grids.

One idea put forth in 1987 by the late theorist Phil Anderson of Princeton University involves putting materials into a quantum spin liquid state, which Anderson proposed could lead to high-temperature superconductivity. The key is the spins of the electrons in each of the material’s atoms, which under certain conditions can be nudged into a state where they become ​frustrated” and unable to arrange themselves into an ordered pattern.

To relieve this frustration, electron spin directions fluctuate in time, only aligning with neighboring spins for short periods of time, like a liquid. It is these fluctuations that may aid in the electron pair formation needed for high-temperature superconductivity.

Pressure provides a way to ​tune” the separation between electron spins and drive a magnet into a frustrated state where magnetism goes away at a certain pressure and a spin liquid emerges, according to Daniel Haskel, the physicist and group leader in Argonne’s X-ray Science Division (XSD) who led a research team through a series of experiments at the APS to do just that. The team included Argonne assistant physicist Gilberto Fabbris and physicists Jong-Woo Kim and Jung Ho Kim, all of XSD.

Haskel is careful to say that his team’s results, recently published in Physical Review Letters, do not conclusively demonstrate the quantum nature of the spin liquid state, in which the atomic spins would continue to move even at absolute zero temperatures — more experiments would be needed to confirm that.

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