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 First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology

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: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>