Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > Quantum fractals at the border of magnetism

Abstract:
Study of quantum phase changes reveals surprising relationship between magnetism and electricity

Quantum fractals at the border of magnetism

Houston, TX | Posted on July 29th, 2010

U.S., German and Austrian physicists studying the perplexing class of materials that includes high-temperature superconductors are reporting this week the unexpected discovery of a simple "scaling" behavior in the electronic excitations measured in a related material. The experiments, which were conducted on magnetic heavy-fermion metals, offer direct evidence of the large-scale electronic consequences of "quantum critical" effects.

The experimental and theoretical results are reported this week in the Proceedings of the National Academy of Science by physicists at Rice University in Houston; the Max Planck Institute for Chemical Physics of Solids and the Max Planck Institute for the Physics of Complex Systems, both in Dresden, Germany; and the Vienna University of Technology in Austria.

"High-temperature superconductivity has been referred to as the biggest unsolved puzzle in modern physics, and these results provide further support to the idea that correlated electron effects -- including high-temperature superconductivity -- arise out of quantum critical points," said Rice physicist Qimiao Si, the group's lead theorist.

"Our experiments clearly show that variables from classical physics cannot explain all of the observed macroscopic properties of materials at quantum critical points," said lead experimentalist Frank Steglich, director of the Max Planck Institute for Chemical Physics of Solids.

The experiments by Steglich's group were conducted on a heavy-fermion metal containing ytterbium, rhodium and silicon that is known as YbRh2Si2 (YRS). YRS is one of the best-characterized and most-studied quantum critical materials.

Quantum criticality refers to a phase transition, or tipping point, that marks an abrupt change in the physical properties of a material. The most common example of an everyday phase change would be the melting of ice, which marks the change of water from a solid to a liquid phase. The term "quantum critical matter" refers to any material that undergoes a phase transition due solely to the jittering of subatomic particles as described by Heisenberg's uncertainty principle. Heavy-fermion metals like YRS are one such material class, and considerable evidence exists that high-temperature superconductors are another.

Scientists are keen to better understand high-temperature superconductivity because the technology could revolutionize electric generators, MRI scanners, high-speed trains and other devices.

High temperature superconductivity typically arises at the border of magnetism, and some physicists believe it originates in the fluctuations associated with magnetic quantum criticality. In magnetic systems such as YRS, traditional theories attempt to explain quantum criticality by considering magnetism alone. In this view, electrons - the carriers of electricity - are considered as microscopic details that play no role in quantum criticality.

In 2001, Si and colleagues proposed a new theory based upon a new type of quantum critical point. Their "local quantum criticality" incorporates both magnetism and charged electronic excitations. A key prediction of the theory is that Fermi volume collapses at a quantum critical point.

"Fermi volume" refers to the combined momenta, or wavelengths, of all the electrons in a crystalline solid. It exists because electrons -- part of the family of elementary particles called "fermions" - must occupy different quantum mechanical states.

The newly reported results about YRS are the culmination of more than seven years' worth of research by Si, Steglich and colleagues. In 2004, they reported the first evidence for the collapse of a Fermi volume in a quantum critical matter, and three years later they reported the first telltale signs of a link between the Fermi-volume collapse and thermodynamic properties in YRS.

In YRS, the transition from one quantum phase to another -- the tipping point -- is marked by a flip between magnetic and nonmagnetic states. By cooling YRS to a set temperature near absolute zero, and adjusting the magnetic field applied to the supercooled YRS, Steglich's team can mark the points along the magnetic continuum that mark both the onset and the end of the Fermi-volume collapse.

In the current study, this method was applied systematically, over a broad range of temperature and magnetic-field settings. To rule out the possibility that irregularities in a particular sample were influencing the results, Steglich's team studied two samples of different qualities and applied an identical set of tests to each. For each sample, the researchers measured the "crossover width," the distance between the beginning and ending points of the Fermi-volume change. The extensive experiments established that the Fermi-volume change is robust, or happens roughly the same way even in different types of samples. The experiments also revealed something entirely new.

"After hundreds of experiments, we plotted the crossover width as a function of temperature, and the plot formed a straight line that ran through the origin," Steglich said. "The effect was the same, regardless of differences between samples, so it is clearly not an artifact of the sample preparation."

"The linear dependence of the Fermi-volume crossover width on the temperature reveals particular quantum-critical scaling properties regarding the electronic excitations," said Si, Rice's Harry C. and Olga K. Wiess Professor of Physics and Astronomy. "It is striking that the electronic scaling is so robust at a magnetic quantum critical point."

Scaling refers to the fact that the mathematics that describes the electronic relationship is similar to the math that describes fractals; the relationships it describes are the same, regardless of whether the scale is large or small. Si said scaling at a quantum critical point is also "dynamical," which means it occurs not only as a function of length scales but also in terms of time scales.

"The experiments provide, for the first time, the evidence for a salient property of local quantum criticality, namely the driving force for dynamical scaling is the Fermi-volume collapse, even though the quantum transition is magnetic," said co-author Silke Paschen, professor and head of the Institute of Solid State Physics at the Vienna University of Technology.

Additional co-authors include Sven Friedmann, Niels Oeschler, Steffen Wirth, Cornelius Krellner and Christoph Geibel, all of the Max Planck Institute for Chemical Physics of Solids, and Stefan Kirchner, a former postdoctoral fellow at Rice University who is now at the Max Planck Institute for the Physics of Complex Systems. The research was supported by the German Research Foundation, the European Research Council, the National Science Foundation and the Welch Foundation.

####

About Rice University
Located in Houston, Rice University is consistently ranked one of America's best teaching and research universities. Known for its "unconventional wisdom," Rice is distinguished by its: size -- 3,279 undergraduates and 2,277 graduate students; selectivity -- 12 applicants for each place in the freshman class; resources -- an undergraduate student-to-faculty ratio of 5-to-1; sixth largest endowment per student among American private research universities; residential college system, which builds communities that are both close-knit and diverse; and collaborative culture, which crosses disciplines, integrates teaching and research, and intermingles undergraduate and graduate work.

For more information, please click here

Contacts:
Jade Boyd
Associate Director and Science Editor
Office of Public Affairs/News & Media Relations
Rice University
(office) 713-348-6778
(cell) 713-302-2447

Copyright © Rice University

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Researchers develop artificial building blocks of life March 8th, 2024

How surface roughness influences the adhesion of soft materials: Research team discovers universal mechanism that leads to adhesion hysteresis in soft materials March 8th, 2024

Two-dimensional bimetallic selenium-containing metal-organic frameworks and their calcinated derivatives as electrocatalysts for overall water splitting March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

Physics

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024

Scientists use heat to create transformations between skyrmions and antiskyrmions January 12th, 2024

Focused ion beam technology: A single tool for a wide range of applications January 12th, 2024

Possible Futures

Two-dimensional bimetallic selenium-containing metal-organic frameworks and their calcinated derivatives as electrocatalysts for overall water splitting March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

The Access to Advanced Health Institute receives up to $12.7 million to develop novel nanoalum adjuvant formulation for better protection against tuberculosis and pandemic influenza March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Academic/Education

Rice University launches Rice Synthetic Biology Institute to improve lives January 12th, 2024

Multi-institution, $4.6 million NSF grant to fund nanotechnology training September 9th, 2022

National Space Society Helps Fund Expanding Frontier’s Brownsville Summer Entrepreneur Academy: National Space Society and Club for the Future to Support Youth Development Program in South Texas June 24th, 2022

How a physicist aims to reduce the noise in quantum computing: NAU assistant professor Ryan Behunin received an NSF CAREER grant to study how to reduce the noise produced in the process of quantum computing, which will make it better and more practical April 1st, 2022

Materials/Metamaterials/Magnetoresistance

How surface roughness influences the adhesion of soft materials: Research team discovers universal mechanism that leads to adhesion hysteresis in soft materials March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Focused ion beam technology: A single tool for a wide range of applications January 12th, 2024

Catalytic combo converts CO2 to solid carbon nanofibers: Tandem electrocatalytic-thermocatalytic conversion could help offset emissions of potent greenhouse gas by locking carbon away in a useful material January 12th, 2024

Announcements

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

The Access to Advanced Health Institute receives up to $12.7 million to develop novel nanoalum adjuvant formulation for better protection against tuberculosis and pandemic influenza March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Research partnerships

Researchers’ approach may protect quantum computers from attacks March 8th, 2024

How surface roughness influences the adhesion of soft materials: Research team discovers universal mechanism that leads to adhesion hysteresis in soft materials March 8th, 2024

'Sudden death' of quantum fluctuations defies current theories of superconductivity: Study challenges the conventional wisdom of superconducting quantum transitions January 12th, 2024

Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024

Quantum nanoscience

Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024

Bridging light and electrons January 12th, 2024

'Sudden death' of quantum fluctuations defies current theories of superconductivity: Study challenges the conventional wisdom of superconducting quantum transitions January 12th, 2024

Physicists ‘entangle’ individual molecules for the first time, hastening possibilities for quantum information processing: In work that could lead to more robust quantum computing, Princeton researchers have succeeded in forcing molecules into quantum entanglement December 8th, 2023

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project