August 20, 2009

Study challenges physics’ Hubbard theory

Canadian scientists are challenging physics' single-band Hubbard theory that's used to predict and calculate behavior of high-temperature superconductors.

University of British Columbia researchers said their findings mark the first compelling evidence challenging the Hubbard model under certain conditions, and could necessitate entirely new theoretical approaches to explaining superconductivity in certain materials.

Single-band Hubbard physics has been used for 20 years to predict how superconducting cuprate (copper oxide) materials accommodate the 'holes' left by electron removal, Darren Peets, lead author of the study, said. "But now it looks like the approaches that underpin a large fraction of the theoretical work in the field just don't work across all the ranges of superconductivity we can study.

The part of the cuprates' superconducting phase diagram we looked at could exhibit less-bizarre behavior, or we could be seeing completely new physics, but in either case the usual theoretical approaches do not work here, he said.

Peets, currently a post-doctoral researcher at Kyoto University in Japan, conducted the research at UBC with Professors Douglas Bonn and George Sawatzky.

The research is reported in the journal Physical Review Letters.