Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Princeton scientists discover exotic quantum state of matter

28.04.2008
'Quantum Hall-like effect' found in a bulk material without an applied magnetic field

A team of scientists from Princeton University has found that one of the most intriguing phenomena in condensed-matter physics -- known as the quantum Hall effect -- can occur in nature in a way that no one has ever before seen.

Writing in the April 24 issue of Nature, the scientists report that they have recorded this exotic behavior of electrons in a bulk crystal of bismuth-antimony without any external magnetic field being present. The work, while significant in a fundamental way, could also lead to advances in new kinds of fast quantum or "spintronic" computing devices, of potential use in future electronic technologies, the authors said.

"We had the right tool and the right set of ideas," said Zahid Hasan, an assistant professor of physics who led the research and propelled X-ray photons at the surface of the crystal to find the effect. The team used a high-energy, accelerator-based technique called "synchrotron photo-electron spectroscopy."

And, Hasan added, "We had the right material."

The quantum Hall effect has only been seen previously in atomically thin layers of semiconductors in the presence of a very high applied magnetic field. In exploring new realms and subjecting materials to extreme conditions, the scientists are seeking to enrich the basis for understanding how electrons move.

Robert Cava, the Russell Wellman Moore Professor of Chemistry and a co-author on the paper, worked with members of his team to produce the crystal in his lab over many months of trial-and-error. "This is one of those wonderful examples in science of an intense, extended collaboration between scientists in different fields," said Cava, also chair of the Department of Chemistry.

"This remarkable experiment is a major home run for the Princeton team," said Phuan Ong, a Princeton professor of physics who was not involved in the research. Ong, who also serves as assistant director of the Princeton Center for Complex Materials, added that the experiment "will spark a worldwide scramble to understand the new states and a major program to manipulate them for new electronic applications."

Electrons, which are electrically charged particles, behave in a magnetic field, as some scientists have put it, like a cloud of mosquitoes in a crosswind. In a material that conducts electricity, like copper, the magnetic "wind" pushes the electrons to the edges. An electrical voltage rises in the direction of this wind -- at right angles to the direction of the current flow. Edwin Hall discovered this unexpected phenomenon, which came to be known as the Hall effect, in 1879. The Hall effect has become a standard tool for assessing charge in electrical materials in physics labs worldwide.

In 1980, the German physicist Klaus von Klitzing studied the Hall effect with new tools. He enclosed the electrons in an atom-thin layer, and cooled them to near absolute zero in very powerful magnetic fields. With the electrons forced to move in a plane, the Hall effect, he found, changed in discrete steps, meaning that the voltage increased in chunks, rather than increasing bit by bit as it was expected to. Electrons, he found, act unpredictably when grouped together. His work won him the Nobel Prize in physics in 1985.

Daniel Tsui (now at Princeton) and Horst Stormer of Bell Laboratories did similar experiments, shortly after von Klitzing's. They used extremely pure semiconductor layers cooled to near absolute zero and subjected the material to the world's strongest magnet. In 1982, they suddenly saw something new. The electrons in the atom-thin layer seemed to "cooperate" and work together to form what scientists call a "quantum fluid," an extremely rare situation where electrons act identically, in lock-step, more like soup than as individually spinning units.

After a year of thinking, Robert Laughlin, now at Stanford University, devised a model that resembled a storm at sea in which the force of the magnetic wind and the electrons of this "quantum fluid" created new phenomena -- eddies and waves -- without being changed themselves. Simply put, he showed that the electrons in a powerful magnetic field condensed to form this quantum fluid related to the quantum fluids that occur in superconductivity and in liquid helium.

For their efforts, Tsui, Stormer and Laughlin won the Nobel Prize in physics in 1998.

Recently, theorist Charles Kane and his team at the University of Pennsylvania, building upon a model proposed by Duncan Haldane of Princeton, predicted that electrons should be able to form a Hall-like quantum fluid even in the absence of an externally applied magnetic field, in special materials where certain conditions of the electron orbit and the spinning direction are met. The electrons in these special materials are expected to generate their own internal magnetic field when they are traveling near the speed of light and are subject to the laws of relativity.

In search of that exotic electron behavior, Hasan's team decided to go beyond the conventional tools for measuring quantum Hall effects. They took the bulk three-dimensional crystal of bismuth-antimony, zapped it with ultra-fast X-ray photons and watched as the electrons jumped out. By fine-tuning the X-rays, they could directly take pictures of the dancing patterns of the electrons on the edges of the sample. The nature of the quantum Hall behavior in the bulk of the material was then identified by analyzing the unique dancing patterns observed on the surface of the material in their experiments.

Kane, the Penn theorist, views the Princeton work as extremely significant. "This experiment opens the door to a wide range of further studies," he said.

The images observed by the Princeton group provide the first direct evidence for quantum Hall-like behavior without external magnetic fields.

"What is exciting about this new method of looking at the quantum Hall-like behavior is that one can directly image the electrons on the edges of the sample, which was never done before," said Hasan. "This very direct look opens up a wide range of future possibilities for fundamental research opportunities into the quantum Hall behavior of matter."

Kitta MacPherson | EurekAlert!
Further information:
http://www.princeton.edu

More articles from Physics and Astronomy:

nachricht Liquid crystals in nanopores produce a surprisingly large negative pressure
25.04.2019 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

nachricht New robust device may scale up quantum tech, researchers say
25.04.2019 | Purdue 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: Full speed ahead for SmartEEs at Automotive Interiors Expo 2019

Flexible, organic and printed electronics conquer everyday life. The forecasts for growth promise increasing markets and opportunities for the industry. In Europe, top institutions and companies are engaged in research and further development of these technologies for tomorrow's markets and applications. However, access by SMEs is difficult. The European project SmartEEs - Smart Emerging Electronics Servicing works on the establishment of a European innovation network, which supports both the access to competences as well as the support of the enterprises with the assumption of innovations and the progress up to the commercialization.

It surrounds us and almost unconsciously accompanies us through everyday life - printed electronics. It starts with smart labels or RFID tags in clothing, we...

Im Focus: Energy-saving new LED phosphor

The human eye is particularly sensitive to green, but less sensitive to blue and red. Chemists led by Hubert Huppertz at the University of Innsbruck have now developed a new red phosphor whose light is well perceived by the eye. This increases the light yield of white LEDs by around one sixth, which can significantly improve the energy efficiency of lighting systems.

Light emitting diodes or LEDs are only able to produce light of a certain colour. However, white light can be created using different colour mixing processes.

Im Focus: Quantum gas turns supersolid

Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.

Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring...

Im Focus: Explosion on Jupiter-sized star 10 times more powerful than ever seen on our sun

A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter

  • Coolest and smallest star to produce a superflare found
  • Star is a tenth of the radius of our Sun
  • Researchers led by University of Warwick could only see...

Im Focus: Quantum simulation more stable than expected

A localization phenomenon boosts the accuracy of solving quantum many-body problems with quantum computers which are otherwise challenging for conventional computers. This brings such digital quantum simulation within reach on quantum devices available today.

Quantum computers promise to solve certain computational problems exponentially faster than any classical machine. “A particularly promising application is the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
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

Fraunhofer FHR at the IEEE Radar Conference 2019 in Boston, USA

09.04.2019 | Event News

 
Latest News

High-efficiency thermoelectric materials: New insights into tin selenide

25.04.2019 | Materials Sciences

Salish seafloor mapping identifies earthquake and tsunami risks

25.04.2019 | Earth Sciences

Using DNA templates to harness the sun's energy

25.04.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>