A Shocking Discovery in High-Temperature Superconductors May Start the New Age of Power
Superconductors are immensely vital to the future of our increasingly electrified world, thanks to their amazing ability to hold an electrical current without resistance.
While scientists have known about high-temperature (still very cold) superconductors known as “cuprates” for decades, they haven't quite solved the mystery of how they achieve zero electrical resistance at temperatures much higher than traditional superconductors.
Now, a new study aims to answer that question—with the help of powerful supercomputers—by introducing a new element to a well-known model used to explore the dynamics of high-temp superconductors.
Many sci-fi promises of our electrified future rely on one important technology: superconductors. These materials are so vital because they exhibit zero electrical resistance, meaning a current can theoretically flow through them forever. That’s an amazingly useful attribute if you want to, say, run MRI machines, create ultra-efficient energy grids, or help build fusion reactors.
Sound too good to be true? Well, unfortunately, it kind of is. Superconductors require bone-shatteringly cold temperatures (as in, approaching absolute zero, or -459.67 degrees Fahrenheit, cold) to tap into those zero electrical resistance superpowers.
Decades after the discovery of superconductors in 1911, scientists figured out that materials (usually metalloids or alloys) needed to be close to absolute zero to exhibit these exciting properties. But in 1986, new materials called copper oxides, or “cuprates,” were discovered to be superconductive at far warmer temperatures. Today, the highest temperature for a superconductor at ambient pressure is -225 degrees Fahrenheit—still cold, but nowhere near absolute zero.
This discovery shocked scientists, and in the decades since, they haven’t quite been able to piece together why these cuprates can achieve superconductivity at such relatively high temperatures. Now, scientists at the Simons Foundation in New York City are taking a crack at explaining this quantum mystery using a familiar model. Usually used in solid-state physics, the 2D Hubbard Model (named after British physicist John Hubbard) looks at materials as if they’re a collection of electrons on a flat quantum chessboard.
Some have argued that high-temperature superconductors are too complicated to be solved by the model, but by implementing “diagonal hops”—which the researchers called a “bishop” on this quantum chessboard—after weeks-long number-crunching by supercomputers, scientists discovered that the model accurately captured key features of superconducting cuprates. This constitutes a potential breakthrough in understanding these immensely important materials.
“After over 30 years of intense effort by the community without many reliable answers, it’s often been argued that solving the Hubbard model would have to wait for a quantum computer,” Simons Foundation Shiwei Zhang, co-author of the paper detailing these results published last week in the journal Science said in a press statement. “This effort will not only advance research in high-temperature superconductivity, but hopefully also spur more research using ‘classical’ computation to explore the wonders of the quantum world.”
The electrons on this “quantum chessboard” have up and down spins. Originally, the simpler model only moved north, south, east, and west, but this new model added the ability for electrons to move diagonally. Electrons filling every space on the chessboard didn’t lead to superconductivity—or any conductivity—and adding (electron doping) or removing (hole doping) electrons formed quantum stripped patterns that only led to varying superconductivity. But with the added the “bishop” to the chessboard, these stripes were suddenly only partially filled, which led to superconductivity.
“Are stripes strictly competing with the superconductivity, or are they causing the superconductivity, or is it something in between?” University of California, Irvine’s Steven White, another co-author of the study, pondered in a press statement. “The current answer is something in between, which is more complicated than either of the other answers.”
In other words, these world-changing cuprates remain difficult materials to understand, but this latest version of the Hubbard model is one big step in the right direction.
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