Study helps unlock mystery of high-temp superconductors: "Evidence has been accumulating that this phase supports an exotic density wave state that may be key to its existence...". A density wave forms in a metal if the fluid electrons themselves crystalize.
Using a scanning tunneling microscope (STM) to visualize the electronic structure of the oxygen sites within a superconductor, the team found a density wave with a d-orbital structure. (The electron density near each copper atom looks a bit like a daisy in the crystallized pattern.) That's especially surprising because most density waves have an s-orbital structure; their electron density is isotropic. "It's not the pattern you would expect," Lawler says.
In this research, Lawler and his colleagues focused on a member of the cuprate class of superconductors called bismuth strontium calcium copper oxide (BSCCO). "We now believe these density waves exist in all cuprates," says Lawler, a theorist whose contribution to the research involved subtle uses of the Fourier transform, a mathematical analysis that's useful when examining amplitude patterns in waves.