How super are superconductors?

Superconductors have zero resistance, so current sent through such a wire loses no energy.

Dutch physicist Heike Kamerlingh Onnes and his collaborators, Cornelis Dorsman, Gerrit Jan Flim and Gilles Holst discovered superconductivity. The research of Johannes Diderik van der Waals -- a fellow countryman and contemporary physicist famous for the forces, molecules, radii and equation of state that bear his name -- helped inspire Onnes’ work. Hugo Christiaan Hamaker, another Dutch scientist, was an experimental physicist famous for his statistical work.

When it was first identified by Dutch physicist Heike Kamerlingh Onnes in 1911, superconductivity flew in the face of established physics. In fact, an entirely new kind of physics, quantum mechanics, would have to be established before anyone had a hope of cracking the mystery of how the phenomenon worked.

Superconductors only function at very cold temperatures, on the order of 39 K for conventional superconductors (the solid mercury wire that Kamerlingh Onnes used had to be cooled below 4.2 K) and below around 130 K for modern, high-temperature superconductors. As for absolute zero, it cannot be achieved artificially, although laser cooling has taken us within one billionth of a degree of it.

Just as superconductors have a critical temperature that separates them from normal conductors, they also have a critical magnetic field that hits them like kryptonite. Too much current will also take superconductors from hero to zero.

Although low critical magnetic fields limited the usefulness of older Type I superconductors for magnetic applications, modern Type II superconductors, such as niobium-titanium (NbTi), can handle much higher magnetic loads. Because they produce higher magnetic fields than, say, electromagnets made from copper wire, they have proven invaluable in MRI machines and proton accelerators.

Good electrical conductors have atomic structures that readily give up electrons, moving them from the valence energy level to the conductance energy level. The result is a large number of free electrons available to carry current. Thus, the two answers essentially describe the same thing.

A conductor is composed of a lattice of atoms, like a tiny jungle gym in which the intersections represent atoms and the connecting rods stand in for interactive forces. A bevy of bosons would be a boon to behold, but bears no relation to a typical conductor. Thanks to Alaskan Sen. Ted Stevens, everyone knows that the Internet is a series of tubes.

The more deformed the lattice of the material is, the more likely it is that it will interfere with the free flow of electrons. The same is also true for higher temperatures, which cause the lattice and its component atoms to vibrate and oscillate faster. Cold, as a rule, decreases resistance.

As a superconductor is cooled, its resistance gradually drops until the critical temperature is reached, after which all resistance abruptly disappears. The substance has undergone a phase transition from conventional material to superconductor.

In a superconductor, two electrons pair off to gain a net advantage when dealing with the ions that make up the material lattice. As the electron passes through the positively charged lattice, it attracts the surrounding atoms toward it. As they bunch up, these atoms create a local area of higher positive charge, which increases the force pulling the second electron forward. Consequently, the energy spent to get through, on average, breaks even.

Superconductors were known for almost half a century before, in 1957, physicists John Bardeen, Leon N. Cooper and John Robert Schrieffer finally advanced a theory that worked. In their honor, this fundamental theory of superconductivity is generally known as the Bardeen-Cooper-Schrieffer, or BCS, theory. In case you're wondering, XTC was a New Wave band from Swindon, England, and "The Aquitaine Progression" was a book by Robert Ludlum, but it sounded cool.

Within a decade or two of the BCS theory being published, researchers began discovering other superconductors, such as heavy-fermion systems and high-temperature superconducting cuprates that broke the model. Today, superconductors that fit the BCS model are called “classical,” while those that don’t are known as "exotic." The means by which these exotic superconductors operate remains the subject of hot debate. "Strange" and "top" are designations used to describe quarks.

Hundreds of materials, including 27 metallic elements -- such as aluminum, lead, mercury and tin -- become superconductors at low temperatures and pressures. Another 11 chemical elements -- including selenium, silicon and uranium -- transition to a superconductive state at low temperatures and high pressures. The magnetic elements chromium, cobalt, iron, manganese and nickel are not superconductors.

The vast majority of superconductors are alloys or compounds.

When cooled below its critical temperature, a Type I superconductor not only exhibits zero electrical resistivity, it also displays perfect diamagnetism. Type II superconductors display perfect diamagnetism while in one superconducting state but not in the other.

A Type II superconductor has two critical magnetic fields. While between these two levels, it reorganizes into a mixed state -- a vortex state -- in which small whirlpools of superconducting current flow around cores of normal material.

Until 1986, when IBM researchers Karl Alexander Müller and Johannes Georg Bednorz ushered in the age of high-temperature superconductors with a barium-lanthanum-copper oxide that achieve zero resistance at 35 K (minus 238 C, minus 397 F), the highest critical temperature achieved by a superconductor was 23 K (minus 250 C, minus 418 F).

Low-temperature superconductors required cooling by liquid helium, which is expensive and difficult to produce, but high-temperature superconductors can use liquid nitrogen, easily made from air, as coolant.

In 2000, Andre Geim Sir Michael Berry won the Ig Nobel Prize for physics by levitating a frog, as well as water and hazelnuts, with a superconductor, using diamagnetism. Alas, the world has yet to behold a superconducting snail, and MRI machines are far too heavy -- and large -- to effectively defenestrate.