Finding materials that exhibit
flow at increasingly higher
temperatures has been a
continuing goal of physicists
since superconductivity was
discovered in 1911.
First superconductor found
First known iron-based superconductor
0 5 10 15 20 25 30 35 40 45 50 55 60 65
operates at temperatures that allow the
use of liquid helium as a coolant
Temperature in kelvins
First recognized copper oxide with
thought. They immediately started creating more iron mixes and comparing
the cuprates with the iron-based family
in search of a common explanation.
Cuprate and contrast
The silvery black pebble that pops from
Paglione’s oven is a crystal that contains
alternating sheets of atoms. Iron-arsenic
layers are stacked on top of films of barium the way noodles and tomato sauce
are layered in lasagna.
Not all iron-based superconductors
combine arsenic with the iron to make
the noodle layer. Some use phosphorus,
selenium or tellurium instead. And not
all have barium; some use other elements
such as lithium or mixes of lanthanum
and oxygen, for example. And some dispense with the sauce altogether.
But all iron-based superconductors
share the layered structure. And it’s
always the layer with the iron that does
the electron shuttling. The other layers
provide some structural support and
keep unneeded electrons out of the way.
Cuprates are also layered, except that
instead of containing iron, the cuprates’
superconducting layers are made of copper and oxygen. The copper and oxygen
bond so that the layers lie flat, while iron-containing layers, say iron and arsenic,
are a bit more three-dimensional, with
arsenic atoms embracing iron atoms
from above and below.
But a good lasagna requires more than
noodles and sauce—it also needs
cheese. Superconductors often add
another ingredient too. In a process
called doping, some atoms are swapped
for others—a bit of cobalt replaces
some iron in one of the iron-based
superconductors, for instance.
All about the magnetism Some scientists believe that the breakdown of a property called
antiferromagnetism may play a big role in high-temperature superconductivity. in an antiferromagnetic
material, the magnetic fields of individual atoms line up in an alternating way (left). Various iron-based
compounds transition (right) from an antiferromagnetic to a superconducting state.