Copper oxide-based superconductors were discovered in 1986. Known as cuprate or high-Tc (for "high critical temperature") superconductors, these materials have a much higher temperature for the transition to zero resistance. But they have proven challenging to explain, since they don't behave as conventional superconductors do. While cuprate superconductors seem to conduct current via paired electrons like conventional superconductors, 26 years later, we still don't know how those pairs are formed.
A new optical examination of a bismuth-based cuprate superconductor has demonstrated that electronic excitations may be the primary driver of the superconducting transition. As described by S. Dal Conte et al. in a new Science paper, the complex interactions between electrons give rise to special quasiparticles. These are states that act as a kind of "glue" between electrons, allowing them to form the pairs that carry the superconducting current. The quasiparticle excitations are sufficient to explain the relatively high temperature of transition between the insulating state and the superconducting state.