Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Old question answered: 'Heavy fermions' aren't really heavy -- they just dawdle

In "heavy fermioin" materials, free electrons that conduct electricity interact strongly with some atoms, pausing to dive to deep energy levels before emerging and moving on. Their slow travel time makes them appear "heavy." Credit: Mohammad Hamidian/Davis Lab
In "heavy fermioin" materials, free electrons that conduct electricity interact strongly with some atoms, pausing to dive to deep energy levels before emerging and moving on. Their slow travel time makes them appear "heavy." Credit: Mohammad Hamidian/Davis Lab

Abstract:
For decades physicists have been fascinated and frustrated by "heavy fermions" -- electrons that move through a conductor as if their mass were up to 1,000 times what it should be.

Now for the first time scientists have produced images of heavy fermion behavior and resolved a theoretical question about its cause.

By Bill Steele

Old question answered: 'Heavy fermions' aren't really heavy -- they just dawdle

Ithaca, NY | Posted on June 4th, 2010

Using an incredibly sensitive scanning tunneling microscope (STM) and a technique called "spectroscopic imaging" that measures the energy levels of electrons under the STM probe, a team led by J.C. Séamus Davis, the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell and director of the Center for Emergent Superconductivity at Brookhaven National Laboratory, determined that electrons moving through a particular uranium compound appear "heavy" because their motion is constantly interrupted by interaction with the uranium atoms.

"This is the first imaging of heavy electron waves by any machine anywhere in the world," Davis said.

The results appear in the June 3 edition of the journal Nature.

The heavy fermion phenomenon is found in a wide variety of materials -- mostly metals combined with rare-earth elements -- in which there is a periodic array of atoms that have a magnetic moment. Many heavy-fermion materials can become superconductors at very low temperatures, a puzzler because magnetism and superconductivity usually don't coexist.

Insight into how these materials work could be a step toward understanding the workings of superconductors in general. And because the ability of a material to absorb heat depends on the mass of its particles, the work could lead to advances in solid-state electronic refrigeration, Davis said.

Davis' team examined URu2Si2, composed of uranium, ruthenium and silicon, which has been a subject of much experimentation and debate since it was first synthesized 25 years ago. At about 55 kelvins (degrees above absolute zero), it begins to show heavy fermion behavior. At 17.5 kelvins it goes through a complex phase transition in which its conductivity, ability to absorb heat and other properties change. Theorists attribute this to a "hidden order" in the material's electrons, but what that might be remained a mystery.

Davis and Cornell graduate students Andrew Schmidt and Mohammad Hamidian varied the voltage between the STM probe and the surface to determine the amount of force needed to pull electrons free from the surface, and from this, the energy levels of the electrons. They scanned samples of URu2Si2 a few nanometers square at a range of temperatures from 17.5 K down.

They found that mobile electrons in the sample, rather than flitting lightly from atom to atom, were interacting strongly with the uranium atoms, in effect diving down into their lower energy levels for picoseconds. This confirms a theoretical explanation for the heavy fermion phenomenon that electrons, which have a tiny magnetic moment, interact with the magnetic moments of uranium atoms. They are not really "heavy," but move as if they were.

Imagine a crowd of frogs hopping across a pond on lily pads. If you know how much push a frog's legs can impart and measure the travel time across the pond, you could calculate the weight of the average frog. But suppose there's an attractive lady frog on every pad, and the frogs stop to chat. Measuring just the travel time, you might conclude that these frogs were all like Mark Twain's famous jumping frog, with bellies full of buckshot.

In addition to answering this question, the demonstration that the spectroscopic imaging STM can image the formation process of heavy electrons opens many more possibilities for further research on heavy-fermion materials, Davis said.

The research was funded by the U.S. Department of Energy, the Canadian Office of Science and the Canadian Institute for Advanced Research.

####

For more information, please click here

Contacts:
Media Contact:
Blaine Friedlander
(607) 254-8093


Cornell Chronicle:
Bill Steele
(607) 255-7164

Copyright © Cornell University

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Sol-gel capacitor dielectric offers record-high energy storage July 30th, 2015

Controlling Dynamic Behavior of Carbon Nanosheets in Structures Made Possible July 30th, 2015

Newly-Developed Polymers Control Size of Nanoparticles during Production Process July 30th, 2015

Detecting small metallic contaminants in food via magnetization: A practical metallic-contaminant detecting system using three high-Tc RF superconducting quantum interference devices (SQUIDs) July 29th, 2015

Controlling phase changes in solids: Controlling phase changes in solids July 29th, 2015

Physics

Meet the high-performance single-molecule diode: Major milestone in molecular electronics scored by Berkeley Lab and Columbia University team July 29th, 2015

Detecting small metallic contaminants in food via magnetization: A practical metallic-contaminant detecting system using three high-Tc RF superconducting quantum interference devices (SQUIDs) July 29th, 2015

Govt.-Legislation/Regulation/Funding/Policy

Sol-gel capacitor dielectric offers record-high energy storage July 30th, 2015

Pakistani Students Who Survived Terror Attack to Attend Weeklong “NanoDiscovery Institute” at SUNY Poly CNSE in Albany July 29th, 2015

Meet the high-performance single-molecule diode: Major milestone in molecular electronics scored by Berkeley Lab and Columbia University team July 29th, 2015

New computer model could explain how simple molecules took first step toward life: Two Brookhaven researchers developed theoretical model to explain the origins of self-replicating molecules July 28th, 2015

Possible Futures

Smaller, faster, cheaper: A new type of modulator for the future of data transmission July 27th, 2015

Researchers predict material with record-setting melting point July 27th, 2015

Global Corrosion Resistant Nano Coatings Market To 2015: Acute Market Reports July 27th, 2015

Global Zinc oxide nanopowders Industry 2015: Acute Market Reports July 25th, 2015

Discoveries

Sol-gel capacitor dielectric offers record-high energy storage July 30th, 2015

Controlling Dynamic Behavior of Carbon Nanosheets in Structures Made Possible July 30th, 2015

Newly-Developed Polymers Control Size of Nanoparticles during Production Process July 30th, 2015

Non-Enzyme Sensor Determines Level of Blood Sugar July 29th, 2015

Announcements

Sol-gel capacitor dielectric offers record-high energy storage July 30th, 2015

Controlling Dynamic Behavior of Carbon Nanosheets in Structures Made Possible July 30th, 2015

Newly-Developed Polymers Control Size of Nanoparticles during Production Process July 30th, 2015

Detecting small metallic contaminants in food via magnetization: A practical metallic-contaminant detecting system using three high-Tc RF superconducting quantum interference devices (SQUIDs) July 29th, 2015

Tools

Publication on Atomic Force Microscopy based nanoscale IR Spectroscopy (AFM-IR) persists as a 2015 top downloaded paper July 29th, 2015

Nanometrics Announces Upcoming Investor Events July 28th, 2015

Reshaping the solar spectrum to turn light to electricity: UC Riverside researchers find a way to use the infrared region of the sun's spectrum to make solar cells more efficient July 27th, 2015

Superfast fluorescence sets new speed record: Plasmonic device has speed and efficiency to serve optical computers July 27th, 2015

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project