|
Princeton scientists discover exotic quantum state of matter
April 25, 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."
Princeton University
"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."
Princeton University
Quantum State News and Current Quantum State Events RSSEUROCORES conference gives cold quantum matter a European twist
Quantum matter has long fascinated the science community as many completely new physical phenomena have emerged from this field. Cold quantum matter can be used for applications such as high-precision clocks, which may run only one second behind per three million years!
McCormick Researchers Take Step Toward Creating Quantum Computers
For now, full-fledged quantum computers are the stuff of science fiction - in last summer's blockbuster movie Transformers, the bad guys use quantum computing to break into the U.S. Army's secure files in just 10 seconds flat.
Physicists team up to learn how quantum mechanical states break down
Researchers at the US Department of Energy's Ames Laboratory, the University of California, Santa Barbara, and Microsoft Station Q have made significant advancements in understanding a fundamental problem of quantum mechanics -- one that is blocking efforts to develop practical quantum computers with processing speeds far superior to conventional computers. Their respective theoretical and experimental studies investigate how microscopic objects lose their quantum-mechanical properties through interactions with the environment.
Scientists discover new method of observing interactions in nanoscale systems
Scientists have used new optical technologies to observe interactions in nanoscale systems that Heisenberg's uncertainty principle usually would prohibit, according to a study published Jan. 17 in the journal Nature.
The quest for a new class of superconductors
Fifty years after the Nobel-prize winning explanation of how superconductors work, a research team from Los Alamos National Laboratory, the University of Edinburgh and Cambridge University are suggesting another mechanism for the still-mysterious phenomenon.
Molecules of positronium observed in the laboratory for the first time
Physicists at UC Riverside have created molecular positronium, an entirely new object in the laboratory. Briefly stable, each molecule is made up of a pair of electrons and a pair of their antiparticles, called positrons.
Quantum analog of Ulam's conjecture can guide molecules, reactions
Like navigating spacecraft through the solar system by means of gravity and small propulsive bursts, researchers can guide atoms, molecules and chemical reactions by utilizing the forces that bind nuclei and electrons into molecules (analogous to gravity) and by using light for propulsion.
Thousands of atoms swap 'spins' with partners in quantum square dance
Physicists at the Commerce Department's National Institute of Standards and Technology (NIST) have induced thousands of atoms trapped by laser beams to swap "spins" with partners simultaneously.
ESA takes steps toward quantum communications
A team of European scientists has proved within an ESA study that the weird quantum effect called 'entanglement' remains intact over a distance of 144 kilometres.
Researchers create new nanotechnology field
A University of Alberta research team has combined two fields of study in nanotechnology to create a third field that the researchers believe will lead to revolutionary advances in computer electronics, among many other areas.
More Quantum State News Articles
 | A History of the American People by Paul M. Johnson |
 | The Journal of Curious Letters (Book One of The 13th Reality Series) by James Dashner |
 | Geons, Black Holes, and Quantum Foam: A Life in Physics by John Archibald Wheeler, Kenneth W. Ford, Kenneth Ford |
 | At Home in the Universe: The Search for the Laws of Self-Organization and Complexity by Stuart Kauffman |
 | Condensed Matter Field Theory by Alexander Altland, Ben Simons |
 | Montauk: The Alien Connection (Montauk) by Stewart Swerdlow |
 | The Connectivity Hypothesis: Foundations of an Integral Science of Quantum, Cosmos, Life, and Consciousness by Ervin Laszlo |
 | The Ninth Cube (1) by Victor Grippi |
 | Quantum Wells, Wires and Dots: Theoretical and Computational Physics of Semiconductor Nanostructures by Paul Harrison |
 | Head First Physics: A Learner's Companion to Mechanics and Practical Physics (Head First) by Heather Lang |
| © 2008 BrightSurf.com |