In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature.

Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4. 2 K., the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride ( MgB < sub > 2 </ sub >), although this material displays enough exotic properties that there is some doubt about classifying it as a " conventional " superconductor.

The Meissner effect does not cause the field to be completely ejected but instead the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material.

From about 1993, the highest temperature superconductor was a ceramic material consisting of thallium, mercury, copper, barium, calcium and oxygen ( HgBa < sub > 2 </ sub > Ca < sub > 2 </ sub > Cu < sub > 3 </ sub > O < sub > 8 + δ </ sub >) with T < sub > c </ sub > = 138 K .< ref >

The first unconventional triplet superconductor, organic material ( TMTSF )< sub > 2 </ sub > PF < sub > 6 </ sub >, was discovered by Denis Jerome and Klaus Bechgaard in 1979.

*, the highest-temperature superconductor ( at ambient pressure ) is mercury barium calcium copper oxide ( HgBa < sub > 2 </ sub > Ca < sub > 2 </ sub > Cu < sub > 3 </ sub > O < sub > x </ sub >), at 138 K and is held by a cuprate-perovskite material ,< ref > possibly 164 K under high pressure .< ref >

It should thus be noted that the placement and subsequent levitation of a magnet above an already superconducting material does not demonstrate the Meissner effect, while an initially stationary magnet later being repelled by a superconductor as it is cooled through its critical temperature does.

In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature.

*, the highest-temperature superconductor ( at ambient pressure ) is mercury barium calcium copper oxide ( HgBa < sub > 2 </ sub > Ca < sub > 2 </ sub > Cu < sub > 3 </ sub > O < sub > x </ sub >), at 135 K and is held by a cuprate-perovskite material, which possibly reaches 164 K under high pressure .< ref >

In 1968, Ashcroft put forward that metallic hydrogen may be a superconductor, up to room temperature (~), far higher than any other known candidate material.

A room-temperature superconductor is a hypothetical material which would be capable of exhibiting superconductivity at operating temperatures above 0 ° C ( 273. 15 K ).

As a result, it becomes a superfluid, and the material through which it flows a superconductor.

During operation, the magnet windings must be cooled below their critical temperature, the temperature at which the winding material changes from the normal resistive state and becomes a superconductor.

A cubical magnet levitating over a superconductor | superconducting material ( this is known as the Meissner effect )

Braunbeck ’ s extension ( 1939 ) states that a system of permanent magnets must also contain diamagnetic material or a superconductor in order to obtain stable, static magnetic levitation or suspension.

Other rooms in the cavity support such features as the " Meteor Defense System ", which uses the superconductor grid embedded in the scrith foundation material to manipulate the magnetic field of the Ringworld's sun to create a solar flare ; it uses this to generate a powerful gas laser, which is capable of destroying everything in its path.

Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure, and this phase is a superconductor at temperatures 6 – 12 K.

* Due to the energy gap, the specific heat of the superconductor is suppressed strongly ( exponentially ) at low temperatures, there being no thermal excitations left.

However, before reaching the transition temperature, the specific heat of the superconductor becomes even higher than that of the normal conductor ( measured immediately above the transition ) and the ratio of these two values is found to be universally given by 2. 5.

It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state.

In most materials diamagnetism is a weak effect, but in a superconductor a strong quantum effect repels the magnetic field entirely, apart from a thin layer at the surface.

Europium becomes a superconductor when it is cooled below 1. 8 K and compressed to above 80 GPa.

It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state.

In 1986, it was discovered that some cuprate-perovskite ceramic materials have a critical temperature above .< ref name = Bednorz > Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors.

The situation is different in a superconductor.

In the 1980s it was shown theoretically with the help of a disorder field theory, in which the vortex lines of the superconductor play a major role, that the transition is of second order within the type II regime and of first order ( i. e., latent heat ) within the type I regime, and that the two regions are separated by a tricritical point.

When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected.

The Meissner effect was given a phenomenological explanation by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided

This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface.

A superconductor with little or no magnetic field within it is said to be in the Meissner state.

The structure of a high-T < sub > c </ sub > superconductor is closely related to perovskite structure, and the structure of these compounds has been described as a distorted, oxygen deficient multi-layered perovskite structure.

The first superconductor found with T < sub > c </ sub > > 77 K ( liquid nitrogen boiling point ) is yttrium barium copper oxide ( YBa < sub > 2 </ sub > Cu < sub > 3 </ sub > O < sub > 7-x </ sub >), the proportions of the 3 different metals in the YBa < sub > 2 </ sub > Cu < sub > 3 </ sub > O < sub > 7 </ sub > superconductor are in the mole ratio of 1 to 2 to 3 for yttrium to barium to copper respectively.

Thus, this particular superconductor is often referred to as the 123 superconductor.

The complex nature of this order parameter allows for many parallels between nematic to smectic phase transitions and conductor to superconductor transitions.

The refrigeration requirements for HTSC and low-temperature superconductor ( LTSC ) toroidal coils for the baseline temperatures of 77 K, 20 K, and 4. 2 K, increases in that order.

The combined costs of conductors, structure and refrigerator for toroidal coils are dominated by the cost of the superconductor.

The dominant cost for SMES is the superconductor, followed by the cooling system and the rest of the mechanical structure.

* April 1986-The term high-temperature superconductor was first used to designate the new family of cuprate-perovskite ceramic materials discovered by Johannes Georg Bednorz and Karl Alexander Müller ,< ref > for which they won the Nobel Prize in Physics the following year.

Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors.

Until recently, only certain compounds of copper and oxygen ( so-called " cuprates ") were believed to have HTS properties, and the term high-temperature superconductor was used interchangeably with cuprate superconductor for compounds such as bismuth strontium calcium copper oxide ( BSCCO ) and yttrium barium copper oxide ( YBCO ).

* April 1986 – The term high-temperature superconductor was first used to designate the new family of cuprate-perovskite ceramic materials discovered by Johannes Georg Bednorz and Karl Alexander Müller, for which they won the Nobel Prize in Physics the following year.

PdH < sub > x </ sub > is a superconductor with a transition temperature T < sub > c </ sub > of about 9 K for x = 1.

* for cooling a high-temperature superconductor to a temperature sufficient to achieve superconductivity

Consider a homogeneous superconductor where there is no superconducting current and the equation for ψ simplifies to:

The central solenoid and toroidal field superconducting magnets designed for the ITER fusion reactor use niobium-tin ( Nb < sub > 3 </ sub > Sn ) as a superconductor.

Superconductors are a subclass of perfect conductors in that they also exhibit the Meissner Effect, an inherently quantum mechanical phenomenon that is responsible for expelling any magnetic field lines present during the superconducting transition, thus making the magnetic field zero in the bulk of the superconductor.