Subscribe free to our newsletters via your
. 24/7 Space News .




ENERGY TECH
Negative resistivity leads to positive resistance in the presence of a magnetic field
by Staff Writers
Atlanta GA (SPX) Dec 14, 2013


File image.

In a paper appearing in Nature's Scientific Reports, Dr. Ramesh Mani, professor of physics and astronomy at Georgia State University, reports that, in the presence of a magnetic field, negative resistivity can produce a positive resistance, along with a sign reversal in the Hall effect, in GaAs/AlGaAs semiconductor devices.

The electrical resistance is a basic property of components known as resistors that occur in electrical circuits. Usually, the resistor serves to limit the electric current - the flow of electrons - to the desired value within the circuit in electronic applications. However, a large current through a resistor can also help to generate heat, and this principle is used in toasters, ovens, space heaters, and window defrosters.

Resistors also occur in sensing applications as in strain gauges, gas sensors, etc., when the resistive element exhibits sensitivity to external stimuli. The resistance of a material depends upon the material property called the resistivity. The material resistivity generally takes on positive values, which indicates that electrical energy is dissipated within the material, when a current is passed through it.

In research that is supported by grants from the U.S. Department of Energy and the U.S. Army Research Office, Mani examined the relation between the resistivity and the resistance of microwave photo-excited, very thin sheets of electrons in the presence of a magnetic field with his colleague Annika Kriisa from Emory University.

The motivation for this work came from the fact that, over the past decade, theoretical physics has concerned itself with the remarkable possibility that the material resistivity can take on negative values in special systems, called two-dimensional electron gases (2DEG), at low temperatures in the presence of a magnetic field, when the 2DEG's are illuminated with microwaves - the same type of microwaves that occur in microwave ovens.

That is, scientists have suggested that cooking a 2DEG with microwaves in a magnetic field can help to produce negative resistivity. Yet, the consequences of a negative resistivity were not well understood. The work of Mani and Kriisa helps to clear up some mysteries.

The relation between the resistivity and the resistance is straightforward in the absence of a magnetic field: a positive resistivity will lead to a positive resistance and a negative resistivity will lead to a negative resistance.

The application of a magnetic field generates something called a Hall effect in the sample that complicates the relation between the resistivity and the resistance at finite magnetic fields. The reason for the complication is that, in a small magnetic field, the Hall effect can be large compared to the resistive effect in very clean 2D electron systems.

In such a situation, the Hall effect decides how the system is going to respond to the negative resistivity. This work by Mani and Kriisa shows that the 2D electron system can show a positive resistance in response to a negative resistivity as the Hall effect reverses its sign.

This result will help to further understand the proposed spectacular properties of systems exhibiting negative resistivity, as it also provides more insight into the intricacies of the Hall effect - an effect discovered by the American scientist E. H. Hall circa 1879.

.


Related Links
Georgia State University
Powering The World in the 21st Century at Energy-Daily.com






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





ENERGY TECH
Deep Carbon Observatory scientists discover quick recipe for producing hydrogen
Washington, DC (SPX) Dec 14, 2013
Scientists in Lyon, a French city famed for its cuisine, have discovered a quick-cook recipe for copious volumes of hydrogen (H2). The breakthrough suggests a better way of producing the hydrogen that propels rockets and energizes battery-like fuel cells. In a few decades, it could even help the world meet key energy needs - without carbon emissions contributing to the greenhouse effect an ... read more


ENERGY TECH
Mining the moon is pie in the sky for China: experts

Ancient crater could hold clues about moon's mantle

Minerals in giant impact crater may be clues to moon's makeup, origin

Silent Orbit for China's Moon Lander

ENERGY TECH
NASA poised to launch Mars atmosphere probe

The Tough Task of Finding Fossils While Wearing a Spacesuit

Mars One Selects Lockheed Martin to Study First Private Unmanned Mission to Mars

SSTL selected for first private Mars mission

ENERGY TECH
European consortium space company to offer 'affordable' trips to space

Planning group calls for National Space Policy in Britain

Quails in orbit: French cuisine aims for the stars

Heat Shield for NASA's Orion Spacecraft Arrives at Kennedy Space Center

ENERGY TECH
China deploys 'Jade Rabbit' rover on moon

The Dragon Has Landed

Chinaese moon rover and lander photograph each other

China's Jade Rabbit lunar rover sends first photos from moon

ENERGY TECH
Altitude of International Space Station raised

NASA mulls spacewalks to fix space station

NASA reports coolant loop problem at ISS

Space station cooling breakdown may delay Orbital launch

ENERGY TECH
Arianespace orders 18 rockets for 2 bn euros

Iran sends second monkey into space

SpaceX to bid for rights to historic NASA launch pad

Arianespace to launch GSAT-15 and GSAT-16 satellites for India

ENERGY TECH
Feature of Earth's atmosphere may help in search for habitable planets

Astronomers discover planet that shouldn't be there

Hot Jupiters Highlight Challenges in the Search for Life Beyond Earth

Astronomers find strange planet orbiting where there shouldn't be one

ENERGY TECH
New sensor tracks zinc in cells

Morphing material has mighty potential

Polymers can be semimetals

A Stopwatch for Electron Flashes




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement