UBC Researchers help define electron behavior in High Temperature Superconductor

Posted: November 24, 2011

UBC researchers have teamed with others at the Advanced Light Source, Lawrence Berkeley National Laboratory to publish a paper in Nature which helps describe the behaviour of electrons in high temperature superconducting cuprates.

The research indicates that high-temperature superconductivity in copper oxides is linked to what they term ‘incoherent excitations’–a discovery that sheds light on the electronic response of these materials before they become superconducting.

The study marks the first time researchers have been able to directly measure when electrons in a super conductor behave as independent well-defined particles, and when they evolve into ill-defined many-body entities.

“We’ve never been able to directly quantify the nature of electron behaviour within these materials across the entire phase diagram–the transition from non-superconducting to superconducting behaviour,” says Associate Professor Andrea Damascelli, Canada Research Chair in Electronic Structure of Solids with the Department of Physics and Astronomy.

“A combination of advanced spectroscopic techniques, and access to very pure cuprate crystals produced at UBC have allowed us to measure what’s going on below the surface of a high-temperature superconducting material through the entire progression of different phases.”

Cuprates normally act as insulators but become superconductors when electrons are removed–a process known as ‘doping’ holes into the material. Physicists consider a material optimally doped when it achieves superconductivity at the highest, most accessible temperature. A material is ‘underdoped’ when its level of doping is less than the level that maximizes the superconducting temperature.

A central debate in the field has focused on whether high-temperature superconductivity–the ability to conduct electricity without resistance at record high temperatures–emerges from a fluid of individual Fermi liquid quasiparticles (the electron-like entities ‘dressed’ by the interactions with their surrounding that give rise to conventional low-temperature superconductivity), or is instead a property connected to the physics of ‘strongly-correlated’ Mott insulators, in which many-body electron behavior wipes quasiparticles completely out of existence.

Damascelli’s team was able to measure a rapid loss of quasiparticle integrity in the material’s electron behavior upon entering the cuprates’ underdoped phase. “This implies that some very important concepts of Fermi liquid models breakdown entering this phase, and that we’ll have to look in other theoretical directions to explain superconductivity.”