Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

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

The International Space Elevator Consortium (ISEC) is proud to announce the 2014 Space Elevator Conference! This annual event will be held at the Museum of Flight in Seattle, Washington from Friday, August 22nd through Sunday, August 24th August 19th, 2014

KaSAM-2014 International Conference (September 7-10, 2014, Kathmandu, Nepal) August 19th, 2014

Success in Intracellular Imaging of Cesium Distribution in Plants Used for Cesium Absorption August 19th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Physics

Promising Ferroelectric Materials Suffer From Unexpected Electric Polarizations: Brookhaven Lab scientists find surprising locked charge polarizations that impede performance in next-gen materials that could otherwise revolutionize data-driven devices August 18th, 2014

Moore quantum materials: Recipe for serendipity - Moore Foundation grant will allow Rice physicist to explore quantum materials August 12th, 2014

Harry Atwater and Albert Polman receive the Julius Springer Prize for Applied Physics 2014: Scientists honored for their pioneering achievements in plasmonics and nanophotonics August 8th, 2014

Diamond defect interior design: Planting imperfections called 'NV centers' at specific spots within a diamond lattice could advance quantum computing and atomic-scale measurement August 5th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Success in Intracellular Imaging of Cesium Distribution in Plants Used for Cesium Absorption August 19th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Promising Ferroelectric Materials Suffer From Unexpected Electric Polarizations: Brookhaven Lab scientists find surprising locked charge polarizations that impede performance in next-gen materials that could otherwise revolutionize data-driven devices August 18th, 2014

Novel chip-based platform could simplify measurements of single molecules: A nanopore-gated optofluidic chip combines electrical and optical measurements of single molecules onto a single platform August 14th, 2014

Possible Futures

Air Force’s 30-year plan seeks 'strategic agility' August 1st, 2014

IBM Announces $3 Billion Research Initiative to Tackle Chip Grand Challenges for Cloud and Big Data Systems: Scientists and engineers to push limits of silicon technology to 7 nanometers and below and create post-silicon future July 10th, 2014

Virus structure inspires novel understanding of onion-like carbon nanoparticles April 10th, 2014

Local girl does good March 22nd, 2014

Discoveries

Success in Intracellular Imaging of Cesium Distribution in Plants Used for Cesium Absorption August 19th, 2014

Сalculations with Nanoscale Smart Particles August 19th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Graphene rubber bands could stretch limits of current healthcare, new research finds August 19th, 2014

Announcements

Сalculations with Nanoscale Smart Particles August 19th, 2014

Life on Mars? Implications of a newly discovered mineral-rich structure August 19th, 2014

Harris & Harris Group Letter to Shareholders on Website August 19th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Tools

Oxford Instruments Asylum Research Receives the 2014 Microscopy Today Innovation Award for blueDrive Photothermal Excitation August 18th, 2014

Laser makes microscopes way cooler: Cooling a nanowire probe with a laser could lead to substantial improvements in the sensitivity of atomic force probe microscopes August 15th, 2014

JPK reports on the use of AFM and advanced fluorescence microscopy at the University of Freiburg August 13th, 2014

Phasefocus reports on the use of their high-precision Lens Profiler for measuring contact lens thickness at the Brien Holden Vision Institute in Sydney, Australia August 13th, 2014

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







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE