Subscribe free to our newsletters via your
. Energy 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








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
Ukraine's Two New Energy Deals

Keeping the lights on

Global energy demand to increase 35 percent: ExxonMobil

Who Is Keeping the Lights on in California?

ENERGY TECH
Can We Turn Unwanted Carbon Dioxide Into Electricity

Deep Carbon Observatory scientists discover quick recipe for producing hydrogen

Negative resistivity leads to positive resistance in the presence of a magnetic field

Lockheed Martin Manufacturing Tanks to Store and Transport Liquefied Natural Gas

ENERGY TECH
Wind energy: TUV Rheinland certifies PowerWind wind turbines

Renewable Energy Infrastructure Fund acquires 16 MW wind power asset from O2

Morgan Advanced Materials Delivers Superior Insulation Solution To Wind Farm

Ethiopia spearheads green energy in sub-Saharan Africa

ENERGY TECH
GE Energy Financial Services Progresses In Solar

Concentrated Photovoltaic Solar Installations Set to Boom in the Coming Years

Greggs proves that solar energy generation is far from a half-baked plan

Quantum waves at the heart of organic solar cells

ENERGY TECH
Ratepayers Could Save $1.7 Billion If Aging Nuclear Plant At Hanford, Washington Is Closed

US Risks Losing Critical Clean Electricity if Nuclear Power Plants Keep Closing at Steady Pace

US takes last shipment of Russian uranium

Company says no danger after fire at US nuclear plant

ENERGY TECH
Ground broken on $6 million Hungarian farm biogas plant

Team reports on US trials of bioenergy grasses

Companies could make the switch to wood power

Turning waste into power with bacteria and loofahs

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
Geoengineering approaches to reduce climate change unlikely to succeed

New long-lived greenhouse gas discovered by University of Toronto chemistry team

French carbon crook on run after bracelet fails

Rapid climate changes, but with a 120 year time lag




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