Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Electron politics: Physicists probe organization at the quantum level

26.04.2012
Physicists show standard ‘quasiparticle’ theory breaks down at ‘quantum critical point’
A new study this week finds that “quantum critical points” in exotic electronic materials can act much like polarizing “hot button issues” in an election. Reporting in Nature, researchers from Rice University, two Max Planck Institutes in Dresden, Germany, and UCLA find that on either side of a quantum critical point, electrons fall into line and behave as traditionally expected, but at the critical point itself, traditional physical laws break down.

“The beauty of the quantum critical point is that even though it’s only one point along the zero temperature axis, what happens at that point dictates how electrons will interact in the material under a broad set of physical conditions,” said study co-author Qimiao Si, a theoretical physicist at Rice University. The new study involved “heavy-fermion metals,” magnetic materials with many similarities to high-temperature superconductors.

Flowing electrons power all the lights, computers and gadgets that are plugged into the world’s energy grids, and physicists have spent more than a century describing how these electrons behave. But long-standing theories that describe how electrons interact in traditional metals and semiconductors have yet to explain the strange electronic properties of heavy-fermion metals, man-made composites that contain precise atomic arrangements of transition metals and rare earth elements.

In the new study, Si collaborated with a group of experimental physicists led by Frank Steglich at the Max Planck Institute for Chemical Physics of Solids. The researchers examined several physical properties at extremely cold temperatures — some as much as 10 times colder than any such previous measurements — to show exactly how the standard theory of electron correlations in metals breaks down at the quantum critical point (QCP). That theory, Landau’s Fermi liquid theory, was first introduced in 1956.

“By measuring the ratio of the thermal to electrical transport near the QCP in one of the most-studied heavy-fermion metals — ytterbium dirhodium disilicide — we found a breakdown in the fundamental concepts of Landau-Fermi liquid theory,” said Steglich, the founding director of the Max Planck Institute for Chemical Physics of Solids.

Quantum particles come in two main varieties — bosons and fermions. Bosons are the quantum equivalent of extroverts; they enjoy one another’s company and can occupy the same quantum space. Fermions are the opposite; no two can occupy the same quantum space, and this defines much of their behavior.

Electrons are fermions, and their tendency to seek quantum elbow room affects the way they organize. It’s important for scientists to understand how they behave in concert because even a small electric current in a tiny wire involves billions upon billions of individual electrons.

Landau-Fermi liquid theory is a mathematical system that allows physicists to describe the actions of many billions of electrons with just a handful of variables. Landau’s vehicle for collapsing the actions of so many particles is something he dubbed a “quasiparticle,” a placeholder that acts like an individual but describes the collective fate of many physical particles.

“One of the tenets of the Landau theory is that this quasiparticle carries the same amount of quantum units of charge and spin as an electron in isolation,” said Si, Rice’s Harry C. and Olga K. Wiess Professor of Physics and Astronomy. “It is not an actual electron, but it behaves like an electron and has the physical status of an electron.”

To show how Landau’s theory breaks down, the new study demonstrated that quasiparticles near a QCP behaved in a way that electrons could not. Electrons have the ability to convey energy as either heat or electricity. Setting up either a temperature or voltage difference in the material provides the means to measure the thermal or electrical conductivity, and the experimental team measured the ratio of the two conductivities at the QCP and found that the quasiparticles there were carrying about 10 percent less thermal conduction than expected.

From the data, Si and fellow theorists Elihu Abrahams and Stefan Kirchner were able to show that the violation in the accepted ratio between heat and electrical conduction occurred only at the QCP; electrons on either side behaved normally.

“This is important because it shows that the breakdown of traditional electron organization occurs at the QCP,” said Kirchner, a theorist from the Max Planck Institute for the Physics of Complex Systems and former postdoctoral fellow at Rice.

The QCP is the point at which the material passes from one phase to another, like ice melting into water, except that the QCP marks a difference between quantum phases.

Abrahams, professor of physics at the University of California, Los Angeles, said, “The finding is unambiguous; new physics is occurring, and the QCP is the culprit.”

The finding adds to the growing body of experimental evidence in support of a theory Si and colleagues offered in 2001 to explain the correlated electron behavior at the QCP.

“At the QCP, magnetism drives quantum fluctuations,” Si said. “Our theory accounts for these in a way that traditional theories like Landau-Fermi liquid theory cannot.”

Si said these quantum fluctuations at the QCP drive the strange electronic behavior that has often been measured in heavy fermion metals, and they may also play a key role in other exotic materials like high-temperature superconductors.

Research co-authors include Heike Pfau, Stephanie Hartmann, Ulrike Stockert, Peijie Sun, Stefan Lausberg, Manuel Brando, Sven Friedemann, Cornelius Krellner, Christoph Geibel and Steffen Wirth, all of the Max Planck Institute for Chemical Physics of Solids.

The research was facilitated by the International Collaborative Center on Quantum Matter, a research collaborative Rice University formed with partner institutions from China, Germany and the United Kingdom. The research was supported by the German Research Foundation, the National Science Foundation, the Robert A. Welch Foundation and the Aspen Center for Physics.

The Nature paper is available at:
http://www.nature.com/nature/journal/v484/n7395/full/nature11072.html

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is known for its “unconventional wisdom.” With 3,708 undergraduates and 2,374 graduate students, Rice’s undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 4 for “best value” among private universities by Kiplinger’s Personal Finance. To read “What they’re saying about Rice,” go to www.rice.edu/nationalmedia/Rice.pdf

Jade Boyd | EurekAlert!
Further information:
http://www.rice.edu

More articles from Physics and Astronomy:

nachricht Tune your radio: galaxies sing while forming stars
21.02.2017 | Max-Planck-Institut für Radioastronomie

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>