Everything about Unconventional Superconductor totally explained
Unconventional superconductors are materials that display
superconductivity but that don't conform to
BCS theory and
Nikolay Bogolyubov theory or its extensions.
The first unconventional triplet superconductor, organic material (TMTSF)
2PF
6,
was discovered by
Denis Jerome and
Klaus Bechgaard in 1979
.
Recent experimental works by
Paul Chaikin's and
Michael Naughton's groups as well as theoretical analysis of their data by
Andrei Lebed have firmly confirmed
unconventional triplet nature of superconducting pairing in (TMTSF)
2X (X=PF
6, ClO
4, ...) organic materials.
The first unconventional singlet d-wave superconductor was discovered by
J.G. Bednorz and
K.A. Müller in 1986. It was a
Lanthanum-based
cuprate perovskite material with critical temperature of approximately 35
K (-238 degrees
Celsius). This was well above the highest critical temperature known at the time (
Tc=23 K) and thus the new family of materials were called
high-temperature superconductors. Bednorz and Müller received the
Nobel prize for Physics for this discovery in 1987.
Since then, many other
high-temperature superconductors have been synthesized. As early as 1987,
superconductivity above 77 K, the boiling point of
nitrogen, was achieved. This is highly significant from the point of view of the
technological applications of superconductivity, because
liquid nitrogen is far less expensive than liquid
helium, which is required to cool
conventional superconductors down to their critical temperature. The current record critical temperature is about
Tc=133
K (-140
°C) at room pressure, and somewhat higher critical temperatures can be achieved at high pressure. Nevertheless at present it's considered unlikely that cuprate perovskite materials will achieve room-temperature superconductivity.
On the other hand, in recent years other unconventional superconductors have been discovered. These include some that don't superconduct at high temperatures, such as the
strontium-ruthenate oxide compounds, but that, like the high-temperature superconductors, are unconventional in other ways (for example, the origin of the attractive force leading to the formation of
Cooper pairs may be different from the one postulated in
BCS theory). In addition to this, superconductors that have unusually high values of
Tc but that are not cuprate perovskites have been discovered. Some of them may be extreme examples of
conventional superconductors (this is suspected of
magnesium diboride, MgB
2, with
Tc=39 K). Others display more unconventional features.
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