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

A drop of water as a model for the interplay of adhesion and stiction June 30th, 2016

No need in supercomputers: Russian scientists suggest a PC to solve complex problems tens of times faster than with massive supercomputers June 30th, 2016

Surprising qualities of insulator ring surfaces: Surface phenomena in ring-shaped topological insulators are just as controllable as those in spheres made of the same material June 30th, 2016

How cancer cells spread and squeeze through tiny blood vessels (video) June 30th, 2016

Physics

A drop of water as a model for the interplay of adhesion and stiction June 30th, 2016

Govt.-Legislation/Regulation/Funding/Policy

A drop of water as a model for the interplay of adhesion and stiction June 30th, 2016

How cancer cells spread and squeeze through tiny blood vessels (video) June 30th, 2016

Nanoscientists develop the 'ultimate discovery tool': Rapid discovery power is similar to what gene chips offer biology June 25th, 2016

Ultrathin, flat lens resolves chirality and color: Multifunctional lens could replace bulky, expensive machines June 25th, 2016

Possible Futures

A drop of water as a model for the interplay of adhesion and stiction June 30th, 2016

No need in supercomputers: Russian scientists suggest a PC to solve complex problems tens of times faster than with massive supercomputers June 30th, 2016

Surprising qualities of insulator ring surfaces: Surface phenomena in ring-shaped topological insulators are just as controllable as those in spheres made of the same material June 30th, 2016

Building a smart cardiac patch: 'Bionic' cardiac patch could one day monitor and respond to cardiac problems June 28th, 2016

Discoveries

A drop of water as a model for the interplay of adhesion and stiction June 30th, 2016

No need in supercomputers: Russian scientists suggest a PC to solve complex problems tens of times faster than with massive supercomputers June 30th, 2016

Surprising qualities of insulator ring surfaces: Surface phenomena in ring-shaped topological insulators are just as controllable as those in spheres made of the same material June 30th, 2016

How cancer cells spread and squeeze through tiny blood vessels (video) June 30th, 2016

Announcements

A drop of water as a model for the interplay of adhesion and stiction June 30th, 2016

No need in supercomputers: Russian scientists suggest a PC to solve complex problems tens of times faster than with massive supercomputers June 30th, 2016

Surprising qualities of insulator ring surfaces: Surface phenomena in ring-shaped topological insulators are just as controllable as those in spheres made of the same material June 30th, 2016

How cancer cells spread and squeeze through tiny blood vessels (video) June 30th, 2016

Tools

How cancer cells spread and squeeze through tiny blood vessels (video) June 30th, 2016

Oxford Instruments and Dresden High Magnetic Field Laboratory collaborate to develop HTS magnet technology components for high field superconducting magnet systems June 29th, 2016

Texas A&M Chemist Says Trapped Electrons To Blame For Lack Of Battery Efficiency: Forget mousetraps — today’s scientists will get the cheese if they manage to build a better battery June 28th, 2016

FEI Launches Helios G4 DualBeam Series for Materials Science: The Helios G4 DualBeam Series features new capabilities to enable scientists and engineers to answer the most demanding and challenging scientific questions June 27th, 2016

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







Car Brands
Buy website traffic