A topography of extremes
On the track of unconventional superconductivity, researchers are
charting unknown territory

Date:
August 27, 2020
Source:
Helmholtz-Zentrum Dresden-Rossendorf
Summary:
Scientists have successfully combined various extreme experimental
conditions in a unique way, revealing exciting insights into
the conducting properties of the crystalline metal CeRhIn5. They
report on their exploration of previously uncharted regions of
the metal's phase diagram, which is considered a promising model
system for understanding unconventional superconductors.



FULL STORY ==========================================================================
An international team of scientists from the Helmholtz-Zentrum Dresden- Rossendorf (HZDR), the Max Planck Institute for Chemical Physics of
Solids, and colleagues from the USA and Switzerland have successfully
combined various extreme experimental conditions in a completely unique
way, revealing exciting insights into the mysterious conducting properties
of the crystalline metal CeRhIn5. In the journal Nature Communications,
they report on their exploration of previously uncharted regions of the
phase diagram of this metal, which is considered a promising model system
for understanding unconventional superconductors.


========================================================================== "First, we apply a thin layer of gold to a microscopically small single crystal. Then we use an ion beam to carve out tiny microstructures. At the
ends of these structures, we attach ultra-thin platinum tapes to measure resistance along different directions under extremely high pressures,
which we generate with a diamond anvil pressure cell. In addition,
we apply very powerful magnetic fields to the sample at temperatures
near absolute zero." To the average person, this may sound like an
overzealous physicist's whimsical fancy, but in fact, it is an actual description of the experimental work conducted by Dr. Toni Helm from
HZDR's High Magnetic Field Laboratory (HLD) and his colleagues from Tallahassee, Los Alamos, Lausanne and Dresden. Well, at least in part,
because this description only hints at the many challenges involved in combining such extremes concurrently. This great effort is, of course,
not an end in itself: the researchers are trying to get to the bottom
of some fundamental questions of solid state physics.

The sample studied is cer-rhodium-indium-five (CeRhIn5), a metal with surprising properties that are not fully understood yet. Scientists
describe it as an unconventional electrical conductor with extremely
heavy charge carriers, in which, under certain conditions, electrical
current can flow without losses.

It is assumed that the key to this superconductivity lies in the
metal's magnetic properties. The central issues investigated by
physicists working with such correlated electron systems include:
How do heavy electrons organize collectively? How can this cause
magnetism and superconductivity? And what is the relationship between
these physical phenomena? An expedition through the phase diagram The physicists are particularly interested in the metal's phase diagram,
a kind of map whose coordinates are pressure, magnetic field strength,
and temperature. If the map is to be meaningful, the scientists have to
uncover as many locations as possible in this system of coordinates,
just like a cartographer exploring unknown territory. In fact, the
emerging diagram is not unlike the terrain of a landscape.

As they reduce temperature to almost four degrees above absolute zero, the physicists observe magnetic order in the metal sample. At this point, they
have a number of options: They can cool the sample down even further and
expose it to high pressures, forcing a transition into the superconducting state. If, on the other hand, they solely increase the external magnetic
field to 600,000 times the strength of the earth's magnetic field, the
magnetic order is also suppressed; however, the material enters a state
called "electronically nematic." This term is borrowed from the physics
of liquid crystals, where it describes a certain spatial orientation of molecules with a long-range order over larger areas. The scientists assume
that the electronically nematic state is closely linked to the phenomenon
of unconventional superconductivity. The experimental environment at HLD provides optimum conditions for such a complex measurement project. The
large magnets generate relatively long-lasting pulses and offer sufficient space for complex measurement methods under extreme conditions.

Experiments at the limit afford a glimpse of the future The experiments
have a few additional special characteristics. For example, working with high-pulsed magnetic fields creates eddy currents in the metallic parts of
the experimental setup, which can generate unwanted heat. The scientists
have therefore manufactured the central components from a special plastic material that suppresses this effect and functions reliably near absolute
zero. Through the microfabrication by focused ion beams, they produce
a sample geometry that guarantees a high-quality measurement signal.

"Microstructuring will become much more important in future
experiments. That's why we brought this technology into the laboratory
right away," says Toni Helm, adding: "So we now have ways to access and gradually penetrate into dimensions where quantum mechanical effects
play a major role." He is also certain that the know-how he and his
team have acquired will contribute to research on high- temperature superconductors or novel quantum technologies.


========================================================================== Story Source: Materials provided by
Helmholtz-Zentrum_Dresden-Rossendorf. Original written by Dr. Bernd
Schro"der. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Toni Helm, Audrey D. Grockowiak, Fedor F. Balakirev, John Singleton,
Jonathan B. Betts, Kent R. Shirer, Markus Ko"nig, Tobias
Fo"rster, Eric D. Bauer, Filip Ronning, Stanley W. Tozer, Philip
J. W. Moll. Non- monotonic pressure dependence of high-field
nematicity and magnetism in CeRhIn5. Nature Communications, 2020;
11 (1) DOI: 10.1038/s41467-020- 17274-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827105932.htm

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