Physicists use electrical noise to investigate high-temperature superconductivity in cuprates

The Cuprate Superconductivity Mystery

Superconductors conduct electricity without resistance, but most require temperatures near absolute zero. Cuprates, discovered in the late 1980s, exhibit superconductivity at higher temperatures, achievable with liquid nitrogen. The mechanism behind this high-temperature superconductivity has remained a subject of debate among physicists for nearly 40 years.

Investigating the Pseudogap State

A study published in Science, led by Milan Allan of Ludwig Maximilian University of Munich and Ingmar Swart of Utrecht University, explored the pseudogap state in cuprates. The pseudogap is characterized by a phenomenon where electrons appear to vanish at energies where they should be present, above the material's superconducting temperature. This 'missing electron' observation has been consistently noted across various experimental probes, but its cause has been unclear.

Competing Explanations

Two primary theories attempt to explain the pseudogap. One theory suggests that electrons become trapped in structures like charge density waves, with superconductivity developing independently. The alternative theory proposes that the missing electrons form Cooper pairs, which are responsible for carrying current in superconductors. In this view, these pairs form before the material becomes fully superconducting, acting as a precursor to the superconducting state.

New Experimental Approach

Previous experimental methods have yielded inconclusive results regarding the pseudogap, often producing 'incoherent' and 'hard to grasp' data. The research team developed a new method involving listening to the faint electrical crackle of current flowing into a cuprate. This approach aims to provide a more direct observation of electron pairing, which could help resolve the long-standing debate.