The pseudogap persists as material superconducts

Jan 27, 2009

For nearly a century, scientists have been trying to unravel the many mysteries of superconductivity, where materials conduct electricity with zero resistance.

Among the many questions: the existence of the pseudogap, a phase that up until now was found in materials as they were cooled to temperatures above the superconducting temperature - the phase where materials superconduct.

An international research team led by Boston College Physicist Vidya Madhavan reports the pseudogap doesn't give way to superconductivity, but persists and co-exists - possibly even competes - with it, they report in the journal Physical Review Letters.

"There is a need to understand the connection between superconductivity and the pseudogap," says Madhavan, an assistant professor of physics. "Is the pseudogap helpful or hurtful? Does it compliment superconductivity or does it compete with it? These are the questions researchers have been asking."

The pseudogap has been closely associated with superconductivity, the point where typically un-joinable electrons match up in perfect pairs; and has been documented to exist at temperatures just above those that give rise to superconductivity. What happens after temperatures drop further and electricity conducts without resistance has been a mystery.

A more in-depth understanding of the pseudogap could explain why some materials superconduct better than others at high temperatures - temperatures above absolute zero, or zero degrees Kelvin, according to researchers. The question has been whether this gap was a precursor to or a competitor with superconductivity.

Madhavan and her colleagues combined two investigative techniques that are typically used independently. Scanning tunneling microscopy - or STM - allows researchers to make images and study the electronic properties of materials at the scale of single atoms. Angle-resolved photoemission spectroscopy - or ARPES - also allows for the study of particles, but in relation to their momentum.

The dual profiles these techniques created of a ceramic high-temperature superconductor known as Bi 2201, a copper oxide, documented that the pseudogap doesn't just precede superconductivity. It continues to co-exist once the material superconducts.

"Researchers have thought that the pseudogap disappeared," said Madhavan, who collaborated with researchers at Tohoku University, in Japan, and the Institute of Physics and National Laboratory for Condensed Matter Physics in Beijing, China. "But both STM and ARPES show us (the pseudogap) in the superconductor state. It co-exists along with superconductivity and we think it is competing with superconductivity,"

The notion of competition implies that the pseudogap's mere presence draws electrons away from the superconductor gap. The exact nature of these competing states poses the next challenge for researchers.

"That we've shown the pseudogap co-exists raises a number of questions," said Madhavan. "If we didn't have the pseudogap, maybe the temperature at which materials superconduct could be higher?"

Finding materials that superconduct at higher temperatures could bring the promise of superconductivity that much closer to practical applications now prohibited by the high cost of super-cooling materials in a lab.

Source: Boston College

Explore further: Information storage for the next generation of plastic computers

add to favorites email to friend print save as pdf

Related Stories

CERN: World-record current in a superconductor

Apr 15, 2014

In the framework of the High-Luminosity LHC project, experts from the CERN Superconductors team recently obtained a world-record current of 20 kA at 24 K in an electrical transmission line consisting of two ...

Recommended for you

Better thermal-imaging lens from waste sulfur

17 minutes ago

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

How to test the twin paradox without using a spaceship

Apr 16, 2014

Forget about anti-ageing creams and hair treatments. If you want to stay young, get a fast spaceship. That is what Einstein's Theory of Relativity predicted a century ago, and it is commonly known as "twin ...

User comments : 0

More news stories

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Robotics goes micro-scale

(Phys.org) —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Researchers discover target for treating dengue fever

Two recent papers by a University of Colorado School of Medicine researcher and colleagues may help scientists develop treatments or vaccines for Dengue fever, West Nile virus, Yellow fever, Japanese encephalitis and other ...