The Ultrafast Promise of 'Warm' Superconductivity

A couple of laptops before the Lenovo that's at this moment producing these very words was a machine that sounded distinctly like a jet engine taking off. It was an HP, at least a few years past its prime and as thick as a lesser encyclopedia volume (for "X" or "Q"). The noise was the fan, a comically loud din capable of waking up my roommates that nonetheless never seemed to sufficiently cool the thing off. A hot summer day often meant a much less productive day as the computer slooooowwwwed wayyyy dowwwwwnnn. Oddly enough, it was the screen that finally gave out.

Heat is the cost of electricity-based information processing. As current moves through wires among circuits carved into substrates of silicon, making its way from point A to point B, not all of it makes it to the destination. There is inherent resistance in those wires, acting as a somewhat literal drag on the passing current, which means it takes more energy to get through the resistance and this extra energy expenditure is dissipated as heat. The microscopic description is of particles cruising through some conductive material and encountering the various atomic ions making up the material itself. These collisions force the loss of kinetic energy. The ions vibrate and, so: heat.

Managing heat is an old problem in computer engineering and, really, one of its most daunting and ubiquitous. The promised land of power efficiency, where little or no current is lost as heat, is the superconductor. This is, as the name implies, a material that's capable of conducting electricity with no loss. A perfect conductor, in other words.

Superconduction is a deep and very old problem. It's also more than just a theory or idealized case. We can make superconductors IRL. The catch is that, so far, it only really works at near-absolute zero temperatures and with extremely purified materials.

The basic idea is that the electrons making up an electrical current undergo a sort of pseudo-phase change at very low temperatures, where they stop behaving as individuals and start acting as sort of just one big particle: a unified choreography.

Conduction is better in colder temperatures no matter what, but superconductors are something extra. As things get colder and colder, eventually a critical point is reached and, very suddenly, electrical resistance will drop to zero. It's pretty strange, actually. And with no resistance, a current might circulate around a loop indefinitely, which has been demonstrated, at least for a couple of years at a time. As an added feature, superconductors lack magnetic fields, leading to effects such as magnetic levitation.

The phenomenon of high-temperature superconductivity, which is just what it sounds, is a good place to start when explaining superconductivity in general. The latest advance in this field came just last week, courtesy of a team of physicists based at the University of Southern California, as described by ​a new paper in the journal Nano Letters. Their technique is based on so-called "superatoms"—aluminum, in this case—that have the ability form Cooper pairs at temperatures of around 100 K (still -280 degrees Fahrenheit, but much warmer than absolute zero.)

A superatom is actually a group of many homogenous atoms, and they have the ability to emulate what are known as Cooper pairs. These are pairings of electrons that, contrary to expectation, attract each other rather than repel. It's these pairings that allow for superconductivity, as the electrons in such a formation start working together, forming linkages that are impervious to the obstructing ions behind resistance.

"Imagine you have a ballroom full of paired-up dancers, only the partners are scattered randomly throughout the room. Your partner might be over by the punch bowl, while you're in the center of the dance floor. But your motions are done in tandem—you are in step with one another," explains USC physicist Vitaly Kresin, the lead researcher behind the new study. "Now imagine everyone changes dance partners every few moments. This is a commonly used analogy for how Cooper pairing works."

A superatom, as a collective of atoms acting as one, comes equipped with super-electron shells. An electron shell in an atom is, in a very loose sense, a layer where we might find orbiting electrons of a certain energy, with each shell having the ability to hold only a certain number of electrons (two then eight then 18 and so on).

So, we have these sorts of clouds around an atomic nucleus at different distances which are full of electron blurs. In a superatom, we find bizarrely huge electron shells as electrons flow around them according to the usual rules but at a much larger scale. Kresin and his team decided to perform some experiments to see if these huge electron shells might exhibit Cooper pairing.

To do so, they blasted their aluminum superatoms with laser pulses, measuring to see how their electrons responded to these boosts of energy. What we'd expect is an even, smooth relationship as more energy is added to the system, the more electrons are knocked out of the atom. This wasn't the case.

Instead, there were bulges where electrons seemed to "hang on" to the atom or to their respective electron shells. These bulges appeared only as temperatures were lowered, suggesting that the electrons had formed Cooper pairings, which helped them stay put even as more and more energy was supplied. And yet, "One-hundred Kelvin might not be the upper-temperature barrier," Kresin offers. "It might just be the beginning."

So, we can imagine conductors in the future being built of strings of these superatoms, providing superconduction at everyday (or close to it) temperatures. It's too late for my old HP, but the promise of cold computing is the promise of waste-free computing, which is huge.