- 4455
- SUPERCONDUCTIVITY - can
we harness it? - Last summer, 2023,
commentators went wild for LK-99, an alleged room-temperature superconductor
that seemed to foreshadow a wondrous age of perfectly efficient power lines and
magnetically levitating trains.
--------------- 4455 - SUPERCONDUCTIVITY - can we harness it?
- Many physicists, meanwhile, kept their
cool. Claims of materials conducting electricity with zero resistance (or
“superconducting”) at everyday temperatures pop up regularly enough that the
community has a name for the phenomenon: unidentified superconducting objects,
or USOs.
-
- Like reports of alien spacecraft sightings,
USOs tend to go unconfirmed. Sure enough, other labs failed to replicate the
LK-99 findings, and the hype soon subsided.
The field is also susceptible to mistakes, misperceptions and
hoaxes. For the second time in three
years, the journal Nature retracted a report of room-temperature
superconductivity from the University of Rochester lab of Ranga Dias, citing
scientific irregularities.
-
- While such claims of remarkable materials
often grab the spotlight, a great deal of superconductivity research seeks to
dig deeper. If searching for room-temperature superconductors is akin to the
high-risk, high-reward search for extraterrestrial life, this more fundamental
side of the field more closely resembles biology. It seeks to better understand the key
ingredients and conditions that underlie the known instances of a fragile and
miraculous phenomenon.
-
- Our understanding of superconductivity did
not come easily, because superconductivity is not easy to understand. Albert
Einstein and Richard Feynman — masters of space-time and quantum theory —
worked on the problem in the 1910s and 1950s, respectively, but couldn’t quite
solve the mystery. The physicists John Bardeen, Leon Cooper and J. Robert
Schrieffer finally cracked it in 1957, almost half a century after the
discovery of the phenomenon.
-
- Superconductivity arises when a negatively
charged electron moving through a material pulls atomic nuclei toward it,
creating a positively charged wave traveling with the electron. This positive
ripple, the quantum version of a sound wave, pulls in a second electron.
-
- The resulting pair of electrons, known as a
“Cooper pair”, obeys different quantum rules than individual electrons do. In
particular, Cooper pairs gain the ability to meld into a unified quantum state
known as a superfluid that doesn’t allow for the particle-on-particle
collisions that normally generate resistance.
-
- Researchers know one basic recipe for
superconductivity: Glue electrons together with sound waves. But are there
other, more exotic recipes — ones with different glues, or even different
particles? And can experimentalists whip them up in the lab? Recently,
researchers have made progress on answering these fundamental questions.
-
- For the last 40 years, one of the biggest
mysteries in superconductivity has been why a family of copper-based materials,
the “cuprates,” can superconduct at temperatures roughly 10 times higher than
those at which normal metals can. What is the glue holding those electron pairs
together?
-
- In 2016,
researchers found underlying the superconductivity when they used one of
the planet’s strongest magnetic fields to pry the pairs of electrons apart. And
in 2022, a new experimental technique
gave researchers their most direct view yet of the “cuprate glue” holding
electrons together confirming that it has nothing to do with sound waves.
-
- Experiments placing one atomically thin
sheet of graphene over another at just the right “magic angle,” have unearthed
a new way to play with superconductivity. Some researchers believe that these
twisted graphene sandwiches showcase a potentially novel electron glue even
stronger than that of the cuprates, while others suspect that sound waves might
still lie at the root of it all.
-
- Other labs are pursuing superconductivity by
pairing up different ingredients. Instead of two electrons, they use an
electron and the space, or “hole”, left
behind when an electron goes missing. Holes are positively charged, so
electrons and holes naturally attract. In that case, the challenge isn’t
getting them together, but rather keeping them apart.
-
- Any of these researchers would be thrilled
if their work someday enabled devices that harnessed the quantum oddity of
superconductivity to build new technologies, but that’s not typically why they
pursue their research. They study superconductivity because it’s an inherently
strange and fascinating phenomenon that is only partially understood. They want
to fully understand it, and push it to its limits, wherever that may lead.
-
-
May 4, 2024 SUPERCONDUCTIVITY - can
we harness it? 4455
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--------------------- --- Sunday, May 5, 2024
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