Electrons in superconductors move together in so-called Cooper pairs. This "pairing" gives
In s-wave superconductors - usually in suchmaterials such as lead, tin, and mercury - Cooper pairs are made up of one electron pointing up and the other down, both of which move “face” towards each other without pure angular momentum. In recent decades, a new class of exotic materials has demonstrated the so-called d-wave superconductivity, in which Cooper pairs have two quanta of angular momentum.
Physicists have put forward the theory of the existence of a thirdtype of superconductor between these two so-called "singlet" states: a p-wave superconductor with one quantum of angular momentum and pairing of electrons with parallel rather than antiparallel spins. This spin-triplet superconductor will be a major breakthrough in quantum computing as it can be used to create Majorana fermions - a unique particle that is itself an antiparticle.
For over 20 years, strontium ruthenate (Sr2RuO4) has been one of the leading candidates for the role of a p-wave superconductor.
Ramshaw and his team decided once and for allto determine whether strontium ruthenate is such a popular p-wave superconductor. Using high-resolution resonant ultrasonic spectroscopy, they discovered that this material is potentially a completely new type of superconductor: the g-wave.
As in previous projects, Ramshaw and Goshused resonance ultrasonic spectroscopy to study the symmetry properties of superconductivity in a strontium ruthenate crystal, which was grown by staff from the Max Planck Institute for Solid State Chemical Physics in Germany.
However, unlike previous attempts, Ramshaw and Ghosh faced a major challenge in conducting the experiment.
“Cooling resonant ultrasound to 1 kelvin (minus -272.15 Celsius) is difficult, and for that we had to build a completely new apparatus,” explains Ghosh.
With a fresh install, the Cornell teammeasured the reaction of the elastic constants of a crystal - essentially the speed of sound in a material - to various sound waves when the material is cooled by a superconducting transition to 1.4 Kelvin (-271.75 ° C).
“This is by far the most accurate resonance ultrasonic spectroscopy data ever obtained at such low temperatures,” Ramshaw said.
Based on the data, scientists have determined thatstrontium ruthenate is what is called a two-component superconductor. This means that the way electrons are bound is so complex that it cannot be described by a single number; he needs direction too.
Previous studies have usednuclear magnetic resonance (NMR) spectroscopy to narrow down the possibilities of what kind of wave material strontium ruthenate can be, effectively eliminating the p-wave as an option. By determining that the material was two-component, Ramshaw's team not only confirmed these findings, but also showed that strontium ruthenate is not an ordinary s- or d-wave superconductor.
Researchers can now use this technique to study other materials to see if they are potential candidates for the p-wave.
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