Researchers detail never-before-seen properties in a family of
superconducting Kagome metals

Date:
February 10, 2023
Source:
Brown University
Summary:
Researchers have used an innovative new strategy combining nuclear
magnetic resonance imaging and a quantum modeling theory to describe
the microscopic structure of Kagome superconductor RbV3Sb5 at 103
degrees Kelvin, which is equivalent to about 275 degrees below 0
degrees Fahrenheit.


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FULL STORY ========================================================================== Dramatic advances in quantum computing, smartphones that only need to be charged once a month, trains that levitate and move at superfast speeds.

Technological leaps like these could revolutionize society, but they
remain largely out of reach as long as superconductivity -- the flow of electricity without resistance or energy waste -- isn't fully understood.


==========================================================================
One of the major limitations for real-world applications of this
technology is that the materials that make superconducting possible
typically need to be at extremely cold temperatures to reach that level
of electrical efficiency. To get around this limit, researchers need to
build a clear picture of what different superconducting materials look
like at the atomic scale as they transition through different states of
matter to become superconductors.

Scholars in a Brown University lab, working with an international team
of scientists, have moved a small step closer to cracking this mystery
for a recently discovered family of superconducting Kagome metals. In
a new study, they used an innovative new strategy combining nuclear
magnetic resonance imaging and a quantum modeling theory to describe
the microscopic structure of this superconductor at 103 degrees Kelvin,
which is equivalent to about 275 degrees below 0 degrees Fahrenheit.

The researchers described the properties of this bizarre state of
matter for what's believed to be the first time in Physical Review
Research. Ultimately, the findings represent a new achievement
in a steady march toward superconductors that operate at higher
temperatures. Superconductors that can operate at room temperature (or
close to it) are considered the holy grail of condensed-matter physics
because of the tremendous technological opportunities they would open in
power efficiency, including in electricity transmission, transportation
and quantum computing.

"If you are ever going to engineer something and make it commercial,
you need to know how to control it," said Brown physics professor Vesna Mitrovi?, who leads a condensed matter NMR group at the University and
is a co-author on the new study. "How do we describe it? How do we tweak
it so that we get what we want? Well, the first step in that is you
need to know what the states are microscopically. You need to start to
build a complete picture of it." The new study focuses on superconductor RbV3Sb5, which is made of the metals rubidium vanadium and antimony. The material earns its namesake because of its peculiar atomic structure,
which resembles a basketweave pattern that features interconnected
star-shaped triangles. Kagome materials fascinate researchers because
of the insight they provide into quantum phenomena, bridging two of the
most fundamental fields of physics -- topological quantum physics and
condensed matter physics.

Previous work from different groups established that this material goes
through a cascade of different phase transitions when the temperature
is lowered, forming different states of matter with different exotic properties. When this material is brought to 103 degrees Kelvin, the
structure of lattice changes and the material exhibits what's known
as a charge-density wave, where the electrical charge density jumps up
and down. Understanding these jumps is important for the development of theories that describe the behavior of electrons in quantum materials
like superconductors.

What hadn't been seen before in this type of Kagome metal was what the
physical structure of this lattice and charge order looked like at the temperature the researchers were looking at, which is highest temperature
state where the metal starts transitioning between different states
of matter.

Using a new strategy combining NMR measurements and a modeling theory
known as density functional theory that's used to simulate the electrical structure and position of atoms, the team was able to describe the new structure the lattice changes into and its charge-density wave.

They showed that the structure moves from a 2x2x1 pattern with a signature
Star of David pattern to a 2x2x2 pattern. This happens because the
Kagome lattice inverts in on itself when the temperature gets extremely
frigid. The new lattice it transitions into is made up largely of separate hexagons and triangles, the researchers showed. They also showed how
this pattern connects when they take one plane of the RbV3Sb5 structure
and rotate it, ``gazing '' into it from a different angle.

"It's as if this one Kagome now becomes these complicated things that
split in two," Mitrovi? said. "It stretches the lattice so that the Kagome becomes this combination of hexagons and triangles in one plane and then
in the next plane over, after you rotate it half a circle, it repeats
itself." Probing this atomic structure is a necessary step to providing
a complete portrait of the exotic states of matter this superconducting material transitions into, the researchers said. They believe the findings
will lead to further prodding on whether this formation and its properties
can help superconductivity or if it's something that should be suppressed
to make better superconductors. The new unique technique they used will
also allow the researchers to answer a whole new set of questions.

"We know what this is now and our next job is to figure out what is the relationship to other bizarre phases at low temperature -- does it help,
does it compete, can we control it, can we make it happen at higher temperatures, if it's useful?" Mitrovi? said. "Next, we keep lowering
the temperature and learning more." The experimental research was
led by Jonathan Frassineti, a joint graduate student between Brown and
the University of Bologna, Pietro Bonfa` from the University of Parma,
and two Brown students: Erick Garcia and Rong Cong.

Theoretical work was led by Bonfa` while all the materials were
synthesized at the University of California Santa Barbara. This research included funding from the National Science Foundation.

* RELATED_TOPICS
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# Physics # Quantum_Physics # Materials_Science #
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* RELATED_TERMS
o Absolute_zero o Magnetic_resonance_imaging
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========================================================================== Story Source: Materials provided by Brown_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Jonathan Frassineti, Pietro Bonfa`, Giuseppe Allodi, Erick Garcia,
Rong
Cong, Brenden R. Ortiz, Stephen D. Wilson, Roberto De Renzi,
Vesna F.

Mitrović, Samuele Sanna. Microscopic nature of the
charge-density wave in the kagome superconductor RbV3Sb5. Physical
Review Research, 2023; 5 (1) DOI: 10.1103/PhysRevResearch.5.L012017 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230210185152.htm

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