Magnetics Business & Technology - July/August 2022 - 20

RESEARCH & DEVELOPMENT
Scientists Uncover Surprising New Clues to Exotic Superconductors' Superpowers
and co-investigator in the Quantum Materials program in Berkeley
Lab's Materials Sciences Division, which provided the funding for
this work. He is also a physics professor at UC Berkeley.
To some, CeCoIn5 might seem like an unlikely model to study
superconducting cuprates. CeCoIn5 contains neither copper
nor oxygen, after all. But despite their differences, cuprates and
CeCoIn5 share some key traits: They are both unconventional superconductors
with electron density or " spatial symmetry " patterns
resembling a four-leaf clover. Such spatial symmetry is like a map
highlighting which parts of the superconductor are most densely
populated by electrons.
The team also knew from other studies that the superconducting
state in CeCoIn5 could be switched on and off with powerful
magnets that are currently available in the laboratory, whereas the
requisite magnetic fields needed to modulate cuprates far exceed
those of even the most sophisticated techniques.
Artist's impression of a magnet levitating above a high-temperature
superconductor cooled with liquid nitrogen. When a magnet is placed
above a superconductor, the superconductor pushes away the magnetic
field, causing the magnet to repel or float. (Credit: ktsdesign/Shutterstock)
A
research team has uncovered new clues into the exotic behavior
of unconventional superconductors - devices that efficiently
carry electrical current with zero resistance in ways that defy our
previous understanding of physics.
" The hope is that our work may lead to a better understanding of
superconductivity, which could find applications in next-gen energy
storage, supercomputing, and magnetic levitation trains, " said
first author Nikola Maksimovic, a graduate student researcher in
Berkeley Lab's Materials Sciences Division and UC Berkeley's
Physics Department.
The work could also help researchers design more powerful
superconducting materials by tuning their chemical makeup at the
atomic level. The team, led by Lawrence Berkeley National Laboratory
(Berkeley Lab) in collaboration with UC Berkeley, reported
their findings in the journal Science.
Conventional superconducting materials like lead or tin become
superconducting at temperatures close to zero on the Kelvin
scale, or minus 523.4 degrees Fahrenheit. But some unconventional
superconductors like cuprates, a type of ceramic metal containing
copper and oxygen, somehow become superconducting at
relatively high temperatures near or above 100 Kelvin (minus 280
degrees Fahrenheit).
For decades, researchers have struggled to understand how
superconducting cuprates work, in part because cuprates are difficult
to grow without defects. What's more is their powerful superconductivity
is challenging to switch off - like a race car that keeps
on going, even when it's in neutral. Scientists therefore need a
tool to help them understand how superconductivity evolves from
different phases at the atomic level, and which formulations have
the most potential for real-world applications.
So for the current study, a research team led by James Analytis
focused on a material made of cerium-cobalt-indium5 (CeCoIn5)
that could mimic a cuprate system. Analytis is a faculty scientist
20 Magnetics Business & Technology * July/August 2022
Turning off the superconducting state in CeCoIn5, the team reasoned,
would allow them to " look under the hood, " and study how
the material's electrons behave in a normal, non-superconducting
state. Since cuprates and CeCoIn5 share similar electronic
density patterns, the team inferred that studying CeCoIn5 in all its
different phases could provide important new clues into the origins
of cuprates' superconducting capabilities.
Image of doped CeCoIn5 samples resting on copper " puck " sample holders.
(Each puck is approximately the size of a silver dollar.) The Berkeley
Lab-led team used spectroscopic techniques at the Advanced Light
Source to image the CeCoIn5 crystals' superconductivity as a function of
chemical composition. (Credit: Image courtesy of former Berkeley Lab
researcher Daniel Eilbott)
" CeCoIn5 is a very useful model system. It's an unconventional
superconductor whose properties are very accessible to experimental
techniques at high magnetic fields, some of which are
not possible in cuprates, " said first author Nikola Maksimovic, a
graduate student researcher in Berkeley Lab's Materials Sciences
Division and the Analytis lab in UC Berkeley's Physics Department.
To
begin testing the material as a potential cuprate model, the
researchers grew more than a dozen single-crystals of CeCoIn5
at their Materials Sciences Division lab, and then fabricated experimental
devices from those crystals at the Molecular Foundry's
National Center for Electron Microscopy facility.
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Magnetics Business & Technology - July/August 2022

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