快猫短视频

IN THE 1980s, 鈥渉igh-temperature superconductors鈥� promised everything from
magnetically levitating trains to resistance-free power lines and cheap MRI
scanners. They have failed to deliver largely because they could not carry
enough current. Now a new material will not only do the key trick of conducting
with zero resistance but has overtaken its rivals on the amount of current it
can carry.

The abilities of the new material, magnesium diboride (MgB₂),
sparked a huge research effort across the world after it was shown to
superconduct earlier this year. The 鈥渙ff-the-shelf鈥� chemical loses all
electrical resistance when cooled to 39 kelvin.

This is still pretty cold, especially compared to the working temperatures of
more than 100 kelvin reached by many chemically complex high-temperature
superconductors. But it is almost double the temperature anyone had managed with
simple metallic compounds. Most importantly, it is possible to use cryogenic
refrigerators to make MgB₂ superconduct, rather than the more expensive
liquid helium
(快猫短视频, 3 March, p 6).

The key test for the new material, however, was how much current it could
carry. Three papers in this week鈥檚 Nature answer that question (vol 411,
p 558, p 561 and p 563).

One team, led by Chang-Beom Eom at the University of Wisconsin at Madison,
accidentally persuaded MgB₂ to carry higher currents than before when
thin films of the material became contaminated with oxygen. In related research,
David Caplin and colleagues at Imperial College in London blasted the compound
with protons. At around 20 kelvin with a strong magnetic field, the resulting
material carried a current to compete with the best available
high-temperature superconductors.

鈥淲hat is needed now is a way, presumably chemical, of junking it up
inexpensively,鈥� says Caplin. 鈥淲e hope to use magnesium diboride in situations
such as open-access magnetic resonance imaging.鈥�

A third group, led by Sungho Jin at Lucent Technologies鈥� Bell Labs in New
Jersey, has successfully fabricated dense, iron-clad superconducting
MgB₂ wires.

According to Paul Grant of the Electric Power Research Institute in Palo
Alto, California, all three discoveries 鈥渕ake substantial progress towards
improving the properties vital to high electric current and magnetic field
补辫辫濒颈肠补迟颈辞苍蝉鈥�.

MgB₂ has other advantages, too. 鈥淵ou can put the powder in a tube,
draw it, roll it and you already have a conductor,鈥� says Bartek Glowacki of
Cambridge University. 鈥淚 am quite excited about these results.鈥� Although there
are plenty of challenges ahead, 鈥渨e are moving in the right direction, with a
bright future鈥�, says Glowacki.