More Evidence Against Phonon-Origin As The Glue In Cuprate Superconductors

This latest result will not settle it, but it is another evidence against phonons as the dominant "glue" for the origin of superconductivity in the cuprate family of high-Tc superconductors. This latest work comes from fast optical measurements on the Bismuth-based cuprate superconductors[1].

The researchers measured the part-in-10-thousand changes over a few thousand femtoseconds and then plugged the numbers into a computer model to gauge which processes were most important in carrying energy through the lattice. Electron-electron interactions such as spin fluctuation should carry energy away much faster than phonons do, the researchers argued, making it possible to separate the different contributions.

The ability to study the reflectivity at different wavelengths was key, Giannetti says. That's because the ultrafast electron-electron processes were too fast to observe in the time traces. However, those processes affect the reflectivity at different wavelengths in different ways-100 femtoseconds after the pulse the material was less reflective at longer wavelengths and more reflective at shorter wavelengths. Taken all together, the data show that phonons aren't needed to explain BSCCO's superconductivity, Giannetti says. Electron-electron interactions are strong enough to do the job all by themselves.

As you can read from the article itself, while this experiment convinces people who are already in the spin-fluctuation camp, those in the phonon camps are not convinced at all due to possible issues in the analysis of the data.

In other words, this is still not the smoking gun, and the debate continues.

Zz.

 [1] S. Dal Conte et al., Science v.335, p.1600 (2012).