October 2019, ScientificAmerican.com 49its existence and its properties. “We built this material on a
computer first, and a calculation told us where to look for it.”
That was the real novelty of LaH 10. Scientists have searched
for high-temperature superconductors for more than a century,
but nearly every breakthrough has come from some combination
of guesswork—essentially, trying out different ingredients and
processes one by one, in hopes of success—and good luck. Only
once before had a computer program prophesied a high-temper-
ature superconductor—H 3 S, another high-pressure compound
found in 2014 that also falls into the hydrogen-bearing class of
“hydrides”—but even in that case its creators were actually trying
to make something else. The diamond-breaking pressures
re quired to keep hydrides intact make it highly unlikely that they
will ever be useful, but the algorithms that anticipated them,
along with other recent computational advances, have the poten-
tial to make the search for more practical superconductors more
systematic, and possibly more fruitful, than ever before.
A THEORY OF SUPERCONDUCTIVITY
“lah 10 waS really a godSend,”^ Somayazulu says, recounting the
years of labor that led to the material’s discovery. Clearly excited
as he recalls the tale, he sounds like he is still trying to believe he
made it. He would still be out there, he says, “lost” and navigat-
ing the wilds with “rough ideas” and “high school chemistry,”
were it not for the new algorithms and their predictions.
Even so, once LaH 10 had been conjured, he still had to figure
out how to test it for superconductivity. Ever since the phenome-
non’s discovery in 1911, when Dutch physicist Heike Kamerlingh
Onnes observed the electrical resistance of a mercury wire
immersed in liquid helium inexplicably vanish at 4.2 kelvins,
findings of new superconducting materials have tended to pre-
cede theories that explain them. Although superconductivity
turns out to be surprisingly common, and many other elements
have since been shown to superconduct (all below 10 kelvins), no
one could begin to make sense of it until quantum mechanics
was developed in the 1920s. The explanation depends on the
electrons responsible for electricity behaving as both localized
particles and spread-out waves, the way quantum mechanics
says all subatomic particles do. On this basis, scientists John Bar-
deen, Leon N. Cooper and John Robert Schrieffer devised a theo-
ry now known as BCS (after their initials) to describe the physics
of superconductors and published it in 1957.
It built on scientists’ basic understanding of current: Inside a
metal, the atoms (actually, atomic nuclei plus some bound elec-NOVEL SUPERCONDUCTORS form inside a diamond anvil cell, kept in the central circular window in this cooling cryostat
at Argonne National Laboratory.