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
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
CWRU directly measures how perovskite solar films efficiently convert light to power
12.01.2017 | Case Western Reserve University
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Power and Electrical Engineering
16.01.2017 | Information Technology
16.01.2017 | Power and Electrical Engineering