Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rice's 'quantum critical' theory gets experimental boost

12.01.2012
Study represents step toward unified theory for quantum phase transformation

New evidence this week supports a theory developed five years ago at Rice University to explain the electrical properties of several classes of materials -- including unconventional superconductors -- that have long vexed physicists.

The findings in this week's issue of Nature Materials uphold a theory first offered in 2006 by physicist Qimiao Si, Rice's Harry C. and Olga K. Wiess Professor of Physics and Astronomy. They represent an important step toward the ultimate goal of creating a unified theoretical description of the quantum behavior of high-temperature superconductors and related materials.

"We now have a materials-based global phase diagram for heavy-fermion systems -- a kind of road map that helps relate the predicted behavior of several different classes of materials," Si said. "This is an important step on the road to a unified theory."

High-temperature superconductivity is one of the greatest unsolved mysteries of modern physics. In the mid-1980s, experimental physicists discovered several compounds that could conduct electricity with zero resistance. The effect happens only when the materials are very cold, but still far above the temperatures required for the conventional superconductors that were discovered and explained earlier in the 20th century.

In searching for a way to explain high-temperature superconductivity, physicists discovered that the phenomenon was one of a larger family of behaviors called "correlated electron effects."

In correlated electron processes, the electrons in a superconductor behave in lockstep, as if they were a single entity rather than a large collection of individuals. These processes bring about tipping points called "quantum critical points" at which materials change phases. These phase changes are similar to thermodynamic phase changes that occur when ice melts or water boils, except they are governed by quantum mechanics.

Materials at the border of magnetism and superconductivity -- including heavy-fermion metals and high-temperature superconductors -- are the prototype systems for quantum critical points.

In 2001, Si and colleagues proposed what has now become the dominant theory to explain correlated electron effects in heavy-fermion systems. Their "local quantum critical" theory concluded that both magnetism and charged electron excitations play a role in bringing about quantum critical points.

Experiments over the past decade have provided overwhelming evidence for the role of both effects. In addition, experiments have shown that quantum critical points fall into different classes for different types of materials, including several nonsuperconductors.

"In light of the experimental evidence, an important question arose as to whether a unifying principle might exist that could explain the behavior of all the classes of quantum critical points that had been observed in heavy-fermion materials," Si said.

In 2006, Si put forward a new theory aimed at doing just that. Experiments two years ago confirmed that the theoretical global phase diagram could explain the quantum critical behavior of YRS -- composites of ytterbium, rhodium and silicon that are among the most-studied quantum critical materials.

In the new Nature Materials paper, a group led by experimental physicist Silke Paschen of Vienna University of Technology in Vienna examined a new material made of cerium, palladium and silicon (CPS). Both YRS and CPS are heavy-fermion compounds; however, YRS is a composite of stacked two-dimensional layers, and CPS has a three-dimensional crystalline structure.

"In YRS, the collapse of charged electronic excitations occurs at the onset of magnetic order," Paschen said. "In CPS, we established a similar collapse of the electronic excitations but inside an ordered phase."

To explain the difference between the observations in CPS and YRS, Si and co-author Rong Yu, a Rice postdoctoral researcher, invoked the effect of dimensionality.

"In systems like YRS, reduced dimensionality enhances the quantum fluctuations between the electrons, and that enhancement influences their collective behavior," Yu said. "In the three-dimensional material, we found that the quantum fluctuations were reduced, and this affected the quantum critical point and the correlated behavior in a way that was predicted by theory."

Si said the linkage between the quantum critical points of CPS and YRS is important for the ultimate question of how to classify and unify quantum criticality.

"Our study not only highlights a rich variety of quantum critical points but also indicates an underlying universality," he said.

Si said it is important to test the theory's ability to correctly predict the behavior of even more materials, and his group is working with Paschen and other experimentalists via the International Collaborative Center on Quantum Matter to carry out those tests.

Co-authors on the Nature Materials paper include J. Custers, K.-A. Lorenser, M. Müller, A. Prokofiev, A. Sidorenkio and H. Winkler, all of Vienna University of Technology; A.M. Strydom of the University of Johannesburg in South Africa; and Y. Shimura and T. Sakakibara, both of the University of Tokyo. The research was supported by the European Research Council, the Austrian Science Foundation, the National Science Foundation and the Welch Foundation.

A high-resolution image is available for download at: http://www.media.rice.edu/images/media/NewsRels/0104_lorenzer_sidorenko2.JPG

CAPTION: Physics graduate students Karl-Anton Lorenzer (left) and Andrey Sidorenko adjust equipment at Vienna University of Technology. CREDIT: F. Aigner/TU Wien

A high-resolution image is available for download at: http://www.media.rice.edu/images/media/NewsRels/0104_winkler_sidorenko.JPG

CAPTION: Vienna University of Technology graduate students Hannes Winkler (left) and Andrey Sidorenko are co-authors of a new paper that sheds light on "correlated electron effects" in heavy fermion materials. CREDIT: F. Aigner/TU Wien

The Nature Materials paper is available at: http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat3214.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 less than 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

David Ruth | EurekAlert!
Further information:
http://www.rice.edu
http://www.rice.edu/nationalmedia/Rice.pdf

More articles from Materials Sciences:

nachricht Carnegie Mellon researchers create soft, flexible materials with enhanced properties
24.05.2019 | Carnegie Mellon University

nachricht Plumbene, graphene's latest cousin, realized on the 'nano water cube'
23.05.2019 | Nagoya University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: New studies increase confidence in NASA's measure of Earth's temperature

A new assessment of NASA's record of global temperatures revealed that the agency's estimate of Earth's long-term temperature rise in recent decades is accurate to within less than a tenth of a degree Fahrenheit, providing confidence that past and future research is correctly capturing rising surface temperatures.

The most complete assessment ever of statistical uncertainty within the GISS Surface Temperature Analysis (GISTEMP) data product shows that the annual values...

Im Focus: The geometry of an electron determined for the first time

Physicists at the University of Basel are able to show for the first time how a single electron looks in an artificial atom. A newly developed method enables them to show the probability of an electron being present in a space. This allows improved control of electron spins, which could serve as the smallest information unit in a future quantum computer. The experiments were published in Physical Review Letters and the related theory in Physical Review B.

The spin of an electron is a promising candidate for use as the smallest information unit (qubit) of a quantum computer. Controlling and switching this spin or...

Im Focus: Self-repairing batteries

UTokyo engineers develop a way to create high-capacity long-life batteries

Engineers at the University of Tokyo continually pioneer new ways to improve battery technology. Professor Atsuo Yamada and his team recently developed a...

Im Focus: Quantum Cloud Computing with Self-Check

With a quantum coprocessor in the cloud, physicists from Innsbruck, Austria, open the door to the simulation of previously unsolvable problems in chemistry, materials research or high-energy physics. The research groups led by Rainer Blatt and Peter Zoller report in the journal Nature how they simulated particle physics phenomena on 20 quantum bits and how the quantum simulator self-verified the result for the first time.

Many scientists are currently working on investigating how quantum advantage can be exploited on hardware already available today. Three years ago, physicists...

Im Focus: Accelerating quantum technologies with materials processing at the atomic scale

'Quantum technologies' utilise the unique phenomena of quantum superposition and entanglement to encode and process information, with potentially profound benefits to a wide range of information technologies from communications to sensing and computing.

However a major challenge in developing these technologies is that the quantum phenomena are very fragile, and only a handful of physical systems have been...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

 
Latest News

On Mars, sands shift to a different drum

24.05.2019 | Physics and Astronomy

Piedmont Atlanta first in Georgia to offer new minimally invasive treatment for emphysema

24.05.2019 | Medical Engineering

Chemical juggling with three particles

24.05.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>