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Researchers: Electrons ‘Puddle’ under High Magnetic Fields

A team of materials scientists and physicists from the DOE’s Argonne National Laboratory, the National High Magnetic Field Laboratory and the National Institute of Standards and Technology has discovered a way to confine the behavior of electrons by using extremely high magnetic fields. The team’s results are published in the journal Nature Communications.

Bhattacharya et al have discovered a way to confine the behavior of electrons by using extremely high magnetic fields. Image credit: Argonne National Laboratory.

Bhattacharya et al have discovered a way to confine the behavior of electrons by using extremely high magnetic fields. Image credit: Argonne National Laboratory.

In metals, electrons in outer orbitals can wander fairly freely. However, when the magnetic field is increased dramatically, the motion of these electrons becomes much more tightly confined. Their behavior looks like figure skaters completing compulsory tight spins and jumps.

The team, led by Argonne National Laboratory scientists Anand Bhattacharya and Brian Skinner, used extremely high magnetic fields — equivalent to those found in the center of neutron stars — to alter electronic behavior.

“The nature of this new state that we see has been debated theoretically for over half a century, but experiments to measure its properties have been hard to come by,” Dr. Bhattacharya said.

To create the very high magnetic field needed, the physicists used the facilities of the National High Magnetic Field Lab in Tallahassee, Florida.

There, they examined crystals of strontium titanate (SrTiO3), similar to synthetic diamond, which has the unusual property of allowing electricity to flow even when electrons are extremely sparse and slow-moving.

“In our study, we examine millimeter-sized SrTiO3 single crystals (dimensions: 7.5 x 7.5 x 0.5 mm), obtained from CrysTec GmbH,” the authors said.

The slow motion of the electrons inside the crystal of strontium titanate makes them particularly susceptible to magnetic forces.

The researchers observed that the quantum properties of the electrons changed dramatically when the crystals were put under high magnetic fields and cooled down to just a few hundredths of a degree above absolute zero.

They proposed that in very high magnetic fields, the electrons form spatially inhomogeneous ‘puddles,’ a surprising finding that was supported by key aspects of the data.

“The result is encouraging for scientists looking to develop a fuller understanding of the unusual properties of certain materials,” Dr. Bhattacharya said.

“When we push the limits to which we can take electrons, new physics emerges.”

“If you think about our understanding of electrons, we understand metals, where electrons move freely, and we also understand the behavior of highly localized electrons,” he said.

“But if you can open the door to those in-between regions, you can make new discoveries.”

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Anand Bhattacharya et al. 2016. Spatially inhomogeneous electron state deep in the extreme quantum limit of strontium titanate. Nature Communications 7, article number: 12974; doi: 10.1038/ncomms12974