Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Pigeonholing quantum phase transitions

06.08.2003


Classification of quantum phenomena critical to high-temp superconductivity



A team of physicists led by researchers at Rice University has developed the first thermodynamic method for systematically classifying quantum phase transitions, mysterious electromagnetic transformations that are widely believed to play a critical role in high-temperature superconductivity.

The new research is described in two papers - one theoretical and one experimental - in the Aug. 8 issue of Physical Review Letters. The theoretical paper predicts that a mathematical irregularity called a divergence occurs at every "quantum critical point," a stage materials pass through as they change phases. The experimental paper reports the observation of such a divergence in the quantum critical points of two metals with very different quantum signatures.


"One of the biggest questions in condensed matter physics today is whether high-temperature superconductivity arises out of quantum critical points," said lead researcher Qimiao Si, associate professor of physics and astronomy at Rice. "Classification of quantum critical points is an important step toward answering this question."

Matter commonly transforms itself via phase changes. Melting ice and boiling water are examples of phase transitions that arise from changes in temperature, which can easily be described using classical physics. Within the past decade, physicists have detected quantum phase transitions, changes that arise entirely from quantum fluctuations -- the jittering of subatomic particles as described by Heisenberg’s uncertainty principle.

Every phase transition, whether classical or quantum, is marked by a change in the way matter is ordered. For example, when ice melts, water molecules change from an ordered crystal lattice to a disordered fluid. In quantum phase transitions, which occur in rare earth metals called heavy fermions, electrons change from magnetic to paramagnetic. As the metals change quantum phases, they pass through a stage known as the "critical point" in which all electrons throughout the material respond collectively and can no longer be regarded as individual particles.

The new theoretical work by Si and Rice graduate student Lijun Zhu, in collaboration with Achim Rosch’s group at the University of Karlsruhe, Germany, sprang from the fact that thermodynamic quantities -- like specific heat -- often diverge at classical critical points. The team predicted that the Grüneisen ratio -- the relative value of thermal expansion to specific heat -- would diverge in a very predictable manner in any material as it approached a quantum critical point.

To test the theory, Si and Zhu collaborated with Frank Steglich’s experimental group from the Max-Planck Institute for Chemical Physics of Solids in Dresden, Germany. Steglich, together with his colleagues John Mydosh, Philipp Gegenwart and Robert Küchler, chose two heavy fermion compounds that are based on cerium and ytterbium. The quantum critical points for each occur at absolute zero, the coldest temperature possible.

Since it is impossible to achieve absolute zero in a laboratory, the team cooled the metals to within a few hundredths of a degree above absolute zero. They found that the Grüneisen ratio diverged as predicted in both metals as they approached absolute zero.

From the divergences, the researchers concluded that the two metals belong to two different classes of quantum phase transition. One of these is the locally-critical quantum phase transition, a new class of quantum phase transition first proposed by Si and colleagues in an article in Nature two years ago.

"If our classification system is born out through experiments on additional materials, the discipline will, for the first time, have a general thermodynamic means to systematically understand quantum critical points," Si said. "Such understandings could prove very valuable for physicists studying high-temperature superconductors."

Materials scientists are interested in superconductors because they conduct electricity with no resistance. In standard conductors, like copper or aluminum, a significant percentage of power is lost due to resistance, the tendency of the wires to convert some electricity into heat. Most superconductors must be cooled to near absolute zero before they superconduct. High temperature superconductors operate at temperatures as high as minus 164 degrees Fahrenheit, far above the boiling point of liquid nitrogen, an important milestone for those interested in designing practical systems that are both technologically and economically feasible.

Heavy fermion metals are prototype systems for quantum criticality. When these metals reach their quantum critical point, the electrons within them act in unison and the effects of even one electron moving through the system cause widespread effects throughout. This is very different from the electron interactions in a common wiring material like copper. It is these collective effects that have increasingly convinced physicists of a possible link between superconductivity and quantum criticality.

Contact: Jade Boyd, jadeboyd@rice.edu

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

More articles from Physics and Astronomy:

nachricht NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center

nachricht Researchers create artificial materials atom-by-atom
28.03.2017 | Aalto University

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: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Transport of molecular motors into cilia

28.03.2017 | Life Sciences

A novel hybrid UAV that may change the way people operate drones

28.03.2017 | Information Technology

NASA spacecraft investigate clues in radiation belts

28.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>