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 Researchers demonstrate three-dimensional quantum hall effect for the first time
19.08.2019 | Singapore University of Technology and Design

nachricht A laser for penetrating waves
19.08.2019 | Helmholtz-Zentrum Dresden-Rossendorf

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 miniature stretchable pump for the next generation of soft robots

Soft robots have a distinct advantage over their rigid forebears: they can adapt to complex environments, handle fragile objects and interact safely with humans. Made from silicone, rubber or other stretchable polymers, they are ideal for use in rehabilitation exoskeletons and robotic clothing. Soft bio-inspired robots could one day be deployed to explore remote or dangerous environments.

Most soft robots are actuated by rigid, noisy pumps that push fluids into the machines' moving parts. Because they are connected to these bulky pumps by tubes,...

Im Focus: Vehicle Emissions: New sensor technology to improve air quality in cities

Researchers at TU Graz are working together with European partners on new possibilities of measuring vehicle emissions.

Today, air pollution is one of the biggest challenges facing European cities. As part of the Horizon 2020 research project CARES (City Air Remote Emission...

Im Focus: Self healing robots that "feel pain"

Over the next three years, researchers from the Vrije Universiteit Brussel, University of Cambridge, École Supérieure de Physique et de Chimie Industrielles de la ville de Paris (ESPCI-Paris) and Empa will be working together with the Dutch Polymer manufacturer SupraPolix on the next generation of robots: (soft) robots that ‘feel pain’ and heal themselves. The partners can count on 3 million Euro in support from the European Commission.

Soon robots will not only be found in factories and laboratories, but will be assisting us in our immediate environment. They will help us in the household, to...

Im Focus: Scientists create the world's thinnest gold

Scientists at the University of Leeds have created a new form of gold which is just two atoms thick - the thinnest unsupported gold ever created.

The researchers measured the thickness of the gold to be 0.47 nanometres - that is one million times thinner than a human finger nail. The material is regarded...

Im Focus: Study on attosecond timescale casts new light on electron dynamics in transition metals

An international team of scientists involving the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg has unraveled the light-induced electron-localization dynamics in transition metals at the attosecond timescale. The team investigated for the first time the many-body electron dynamics in transition metals before thermalization sets in. Their work has now appeared in Nature Physics.

The researchers from ETH Zurich (Switzerland), the MPSD (Germany), the Center for Computational Sciences of University of Tsukuba (Japan) and the Center for...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

The power of thought – the key to success: CYBATHLON BCI Series 2019

16.08.2019 | Event News

4th Hybrid Materials and Structures 2020 28 - 29 April 2020, Karlsruhe, Germany

14.08.2019 | Event News

What will the digital city of the future look like? City Science Summit on 1st and 2nd October 2019 in Hamburg

12.08.2019 | Event News

 
Latest News

Stanford builds a heat shield just 10 atoms thick to protect electronic devices

19.08.2019 | Information Technology

Researchers demonstrate three-dimensional quantum hall effect for the first time

19.08.2019 | Physics and Astronomy

Catalysts for climate protection

19.08.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>