Featured Research

from universities, journals, and other organizations

Electrical Conductivity Stopped Cold By A Hint Of Disorder

Date:
June 16, 2008
Source:
CNRS
Summary:
Physicists observe small defects changing some conducting materials suddenly into insulating materials. These results will make it possible to better understand the role of disorder in the electrical properties of certain materials.

With tiny modifications, such as the introduction of impurities or defects, some conducting materials suddenly become insulating. For Philip Anderson, 1977 Physics Nobel Prize winner, the minor disorder introduced by impurities is enough to completely stop electron movement inside a solid. Anderson's hypothesis had been proved indirectly, but the phenomenon had never been directly observed with particles such as atoms or electrons until recently, when it was witnessed by CNRS researchers Alain Aspect (1) and Philippe Bouyer and their team at the Institut d'Optique (2). They have, for the first time, shown atoms subjected to minor disorder coming to a complete stop. Published in the journal Nature, these results will make it possible to better understand the role of disorder in the electrical properties of certain materials.

Introducing disorder to certain conducting materials is sometimes enough to make them suddenly become insulating. On our scale, that would be like saying that a few blades of grass scattered haphazardly over a golf course could stop a full-speed golf ball in its tracks. Admittedly, this would a surprising situation, and at our macroscopic scale, small perturbations can slow the movement of material objects, but can never stop them. But this is different at a microscopic level, where matter can also behave like a wave. In a perfectly ordered solid, an electron moves freely without being disturbed by the underlying regular crystal structure. In disordered solids, however, any flaw will diffuse the matter wave in multiple directions.

Combining all these disorder-generated waves can lead to a wave that does not propagate and remains frozen in the crystal. The electrons (or the atoms) stop their movement, which, in the case of electrons, turns the material into an insulator. Envisioned by Anderson in 1958, this scenario emphasizes the fundamental role of disorder as well as the relevance of studying the electrical properties of disordered materials like amorphous silicon.

In light of the fundamental discoveries made in the 1930s about semi-conductors that led to the invention of the transistor and then to integrated circuits, Anderson's model created strong interest among physicists. While theoretical physicists strived to understand its underlying nature and its significance, experimental physicists tried to observe the phenomenon. Even though convincing experiments existed, direct observation of particle matter located in a weak disorder remained an unattainable goal.

First direct evidence of the Anderson scenario

French researchers at LCFIO took on the challenge by constructing a simple model of the situation that could lead to this phenomenon, called "Anderson localization." In their experiment, ultra-cold (3) atoms play the role of electrons, while the disordered environment is replaced by a perfectly controlled disorder created by light from a laser beam. With the help of a waveguide, the atoms are limited to unidirectional movement. Without disorder, the atoms propagate freely, but when disorder is introduced, all atomic movement stops within a fraction of a second. The researchers then observed the atomic density profile. Its exponential form is characteristic of the scenario envisioned by Anderson (see figure below). By varying the experimental parameters, the researchers were also able to test the theoretical model developed by Laurent Sanchez-Palencia's team at the atomic optics group.

Armed with results obtained from a radically simplified scenario, the physicists at the Institut d'optique now plan on addressing more complex situations in which atoms can move in a plane, or even in the three directions of space. For these conditions approaching those of real materials, theory can not currently precisely predict all situations; experiments alone constitute a type of quantum simulator that can provide part of the answer. Maybe then, by transferring these results to electrons, it will be possible to better define the behavior of these particles in disordered environments. Such results could, in the long run, improve amorphous silicon-based electronic devices, for example.

Used notably in TFT-LCD screens and in some photovoltaic cells, amorphous silicon is significantly less expensive to produce, but currently less effective than the crystalline silicon that forms the base of high performance electronic devices.

(1) CNRS gold medal, 2005.

(2) A team at the atomic optics group which is part of the Laboratoire Charles Fabry de l'Institut d'optique (LCFIO, CNRS / Universitι Paris 11/Institut Optique graduate school).

(3) These ultra-cold atoms are in the form of a diluted Bose-Einstein condensate, formed from several thousand atoms described by the same wave function, making it possible to observe the atomic density profile.


Story Source:

The above story is based on materials provided by CNRS. Note: Materials may be edited for content and length.


Journal Reference:

  1. Billy et al. Direct observation of Anderson localization of matter waves in a controlled disorder. Nature, 2008; 453 (7197): 891 DOI: 10.1038/nature07000

Cite This Page:

CNRS. "Electrical Conductivity Stopped Cold By A Hint Of Disorder." ScienceDaily. ScienceDaily, 16 June 2008. <www.sciencedaily.com/releases/2008/06/080612145635.htm>.
CNRS. (2008, June 16). Electrical Conductivity Stopped Cold By A Hint Of Disorder. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2008/06/080612145635.htm
CNRS. "Electrical Conductivity Stopped Cold By A Hint Of Disorder." ScienceDaily. www.sciencedaily.com/releases/2008/06/080612145635.htm (accessed July 22, 2014).

Share This




More Matter & Energy News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) — The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) — The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) — President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) — Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins