Physicists report experimental evidence with the potential to transform multiple fields

Physicists have reported the first experimental evidence that explains the unusual electronic behavior behind the world's thinnest superconductor. The material team is investigating has multiple applications thanks to its ability to conduct electricity with extreme efficiency. The superconductor is extremely thin at only a single atomic layer thick.The work was made possible thanks to new instrumentation available at only a few facilities around the world. Physicists on the team believe data could help guide the development of better superconductors, potentially transforming medical diagnostics, quantum computing, and energy transport. The material the team investigated is part of a class of superconductors that become superconducting at temperatures an order of magnitude higher than their conventional counterparts.

Typical superconductors have to be chilled to temperatures of around 10 Kelvins (K) to function. The material researchers worked with is part of a group known as high-temperature superconductors that aren't fully understood. Researcher Ricardo Comin says microscopic excitations and dynamics are essential to understanding superconductivity, but many questions remain unanswered despite three decades of research. In 2015 a new type of high-temperature superconductor was discovered consisting of a sheet of iron selenide one atomic layer thick that was capable of superconducting at 65 K.

Scientists found that bulk samples of the material superconductive at a significantly lower temperature of 8 K. The discovery led to an investigative rush to decode the secrets of the world's thinnest superconductor. Scientists know that in conventional superconductors, the so-called glue that holds the pairs of electrons together is derived from the motion of atoms within the material. In high-temperature semiconductors, the glue holding the electrons together is different.

The hypothesis suggests that the glue is related to a property of electrons called spin. The spin can be thought of as an elementary magnet with the idea that in a high-temperature superconductor, electrons can pick up some of the energy from the spins, known as spin excitations. The energy is the glue that is used to pair up. Previously, physicists thought it was impossible to detect or measure spin excitations in material only an atomic layer thick.

However, in the new study, physicists were able to detect spin excitations and showed that the spin dynamics in the ultra-thin sample were significantly different from those in the bulk sample. They found that the energy of the fluctuating spins in the ultra-thin sample was much higher to the tune of four or five times in the energy of the spin in the bulk sample. The study shows the first experimental evidence of the presence of spin excitations in anatomically thin material.