A team of international physicists that includes researchers from the National Institute of Standards and Technology (NIST) has found experimental evidence of a highly sought-after type of arrangement of atomic magnetic moments, or spins, in a series of materials.
Their work, one of the very few studies of this particular spin state, which has been postulated as a possible underlying mechanism for high-temperature superconductivity, may eventually serve as a test of current and future theoretical models of exotic spin states.
At the NIST Center for Neutron Research (NCNR) and the Hahn-Meitner Institute in Berlin, Germany, the scientists used intense beams of neutrons to probe a series of antiferromagnets, materials in which each spin--an intrinsic property of an atom that produces a tiny magnetic field called a magnetic "moment"--cancels another, giving the material a net magnetic field of zero.
The results, described in the Aug. 26 online edition of Nature Materials,* revealed evidence of a rare and pporly understood "quantum paramagnetic" spin state, in which neighboring spins pair up to form "entangled spin singlets" that have an ordered pattern and that allow the material to weakly respond to an outside magnetic field--i.e., become paramagnetic.
The antiferromagnets used in this work are composed mainly of zinc and copper, and are distinguished by their proportions of each, with the number of copper ions determined by the number of zinc ions. At the atomic level, the material is formed of many repeating layers. The atoms of each layer are arranged into a structure known as a "kagome lattice," a pattern of triangles laid point-to-point whose basic unit resembles a six-point star.
Physicists have been studying antiferromagnets with kagome structures over the last 20 years because they suspected these materials harbored interesting spin structures. But good model systems, like the zinc/copper compounds used by this group, had not been identified.
At the NCNR, the researchers determined how varying concentrations of zinc and copper and varying temperatures affected fluctuations in the way the spins are arranged in these materials. Using a neutron spectrometer at the Hahn-Meitner Institute, they also investigated the effect of external magnetic fields of varying strengths. The group uncovered several magnetic phases in addition to the quantum paramagnetic state and were able to construct a complete phase diagram as a function of the zinc concentration and temperature. They are planning further experimental and theoretical studies to learn more about the kagome system.
This work was led by S.-H. Lee at the University of Virginia. The other participating institutions are the University of Fukui in Japan, and the Hahn-Meitner Institute and the Technical University of Berlin, both in Germany.
10/19/2007
A New Look At The Proton
Dutch researcher Paul van der Nat investigated more than three million collisions between electrons and protons. In his PhD thesis he demonstrates -for the first time– that the spin contribution of quarks to the proton can be studied by examining collisions in which two particles (hadrons) are produced.
The spin of a particle can most easily be compared to the rotating movement of a spinning top.
In the HERMES experiment at the HERA particle accelerator in Hamburg, physicists are investigating how the spin of protons can be explained by the characteristics of their building blocks: quarks and gluons.
Van der Nat investigated a method to measure the contribution of the spin of the quarks to the total spin of the proton, independent of the contribution of the spin of the gluons. For this a quark is shot out of the proton by an electron from the particle accelerator, as a result of which two hadrons are formed.
The direction and amount of motion of these two hadrons is accurately measured. This method, which Van der Nat applied for the first time, turned out to be successful.
Spin is a characteristic property of particles, just like matter and electrical charge. Spin was discovered in 1925, by the Dutch physicists Goudsmit and Uhlenbeck. In 1987, scientists at CERN in Geneva discovered that only a small fraction of the proton's spin is caused by the spin of its constituent quarks.
The HERMES experiment was subsequently set up to find this missing quantity of spin, and has been running since 1995. It is expected that spin will play an increasingly important role in many applications. The MRI scanner is a well-known example of an application in which the spin of protons plays a key role.
Adapted from materials provided by Netherlands Organization for Scientific Research.
The spin of a particle can most easily be compared to the rotating movement of a spinning top.
In the HERMES experiment at the HERA particle accelerator in Hamburg, physicists are investigating how the spin of protons can be explained by the characteristics of their building blocks: quarks and gluons.
Van der Nat investigated a method to measure the contribution of the spin of the quarks to the total spin of the proton, independent of the contribution of the spin of the gluons. For this a quark is shot out of the proton by an electron from the particle accelerator, as a result of which two hadrons are formed.
The direction and amount of motion of these two hadrons is accurately measured. This method, which Van der Nat applied for the first time, turned out to be successful.
Spin is a characteristic property of particles, just like matter and electrical charge. Spin was discovered in 1925, by the Dutch physicists Goudsmit and Uhlenbeck. In 1987, scientists at CERN in Geneva discovered that only a small fraction of the proton's spin is caused by the spin of its constituent quarks.
The HERMES experiment was subsequently set up to find this missing quantity of spin, and has been running since 1995. It is expected that spin will play an increasingly important role in many applications. The MRI scanner is a well-known example of an application in which the spin of protons plays a key role.
Adapted from materials provided by Netherlands Organization for Scientific Research.
Superconducting Quantum Computing Cable Created
Physicists at the National Institute of Standards and Technology (NIST) have transferred information between two "artificial atoms" by way of electronic vibrations on a microfabricated aluminum cable, demonstrating a new component for potential ultra-powerful quantum computers of the future.
The setup resembles a miniature version of a cable-television transmission line, but with some powerful added features, including superconducting circuits with zero electrical resistance, and multi-tasking data bits that obey the unusual rules of quantum physics.
The resonant cable might someday be used in quantum computers, which would rely on quantum behavior to carry out certain functions, such as code-breaking and database searches, exponentially faster than today's most powerful computers.
Moreover, the superconducting components in the NIST demonstration offer the possibility of being easier to manufacture and scale up to a practical size than many competing candidates, such as individual atoms, for storing and transporting data in quantum computers.
Unlike traditional electronic devices, which store information in the form of digital bits that each possess a value of either 0 or 1, each superconducting circuit acts as a quantum bit, or qubit, which can hold values of 0 and 1 at the same time. Qubits in this "superposition" of both values may allow many more calculations to be performed simultaneously than is possible with traditional digital bits, offering the possibility of faster and more powerful computing devices. The resonant section of cable shuttling the information between the two superconducting circuits is known to engineers as a "quantum bus," and it could transport data between two or more qubits.
The NIST work is featured on the cover of the Sept. 27 issue of Nature. The scientists encoded information in one qubit, transferred this information as microwave energy to the resonant section of cable for a short storage time of 10 nanoseconds, and then successfully shuttled the information to a second qubit.
"We tested a new element for quantum information systems," says NIST physicist Ray Simmonds. "It's really significant because it means we can couple more qubits together and transfer information between them easily using one simple element."
The NIST work, together with another letter in the same issue of Nature by a Yale University group, is the first demonstration of a superconducting quantum bus. Whereas the NIST scientists used the bus to store and transfer information between independent qubits, the Yale group used it to enable an interaction of two qubits, creating a combined superposition state. These three actions, demonstrated collectively by the two groups, are essential for performing the basic functions needed in a superconductor-based quantum information processor of the future.
In addition to storing and transferring information, NIST's resonant cable also offers a means of "refreshing" superconducting qubits, which normally can maintain the same delicate quantum state for only half a microsecond. Disturbances such as electric or magnetic noise in the circuit can rapidly destroy a qubit's superposition state. With design improvements, the NIST technology might be used to repeatedly refresh the data and extend qubit lifetime more than 100-fold, sufficient to create a viable short-term quantum computer memory, Simmonds says. NIST's resonant cable might also be used to transfer quantum information between matter and light -- microwave energy is a low-frequency form of light -- and thus link quantum computers to ultra-secure quantum communications systems.
If they can be built, quantum computers -- harnessing the unusual rules of quantum mechanics, the principles governing nature's smallest particles -- might be used for applications such as fast and efficient code breaking, optimizing complex systems such as airline schedules, making counterfeit-proof money, and solving complex mathematical problems. Quantum information technology in general allows for custom-designed systems for fundamental tests of quantum physics and as-yet-unknown futuristic applications.
A superconducting qubit is about the width of a human hair. NIST researchers fabricate two qubits on a sapphire microchip, which sits in a shielded box about 8 cubic millimeters in size. The resonant section of cable is 7 millimeters long, similar to the coaxial wiring used in cable television but much thinner and flatter, zig-zagging around the 1.1 mm space between the two qubits. Like a guitar string, the resonant cable can be stimulated so that it hums or "resonates" at a particular tone or frequency in the microwave range. Quantum information is stored as energy in the form of microwave particles or photons.
The NIST research was supported in part by the Disruptive Technology Office.
*M.A. Sillanpää, J.I. Park, and R.W. Simmonds. 2007. Coherent quantum state storage and transfer between two phase qubits via a resonant cavity. Nature, Sept. 27.
Adapted from materials provided by National Institute of Standards and Technology.
The setup resembles a miniature version of a cable-television transmission line, but with some powerful added features, including superconducting circuits with zero electrical resistance, and multi-tasking data bits that obey the unusual rules of quantum physics.
The resonant cable might someday be used in quantum computers, which would rely on quantum behavior to carry out certain functions, such as code-breaking and database searches, exponentially faster than today's most powerful computers.
Moreover, the superconducting components in the NIST demonstration offer the possibility of being easier to manufacture and scale up to a practical size than many competing candidates, such as individual atoms, for storing and transporting data in quantum computers.
Unlike traditional electronic devices, which store information in the form of digital bits that each possess a value of either 0 or 1, each superconducting circuit acts as a quantum bit, or qubit, which can hold values of 0 and 1 at the same time. Qubits in this "superposition" of both values may allow many more calculations to be performed simultaneously than is possible with traditional digital bits, offering the possibility of faster and more powerful computing devices. The resonant section of cable shuttling the information between the two superconducting circuits is known to engineers as a "quantum bus," and it could transport data between two or more qubits.
The NIST work is featured on the cover of the Sept. 27 issue of Nature. The scientists encoded information in one qubit, transferred this information as microwave energy to the resonant section of cable for a short storage time of 10 nanoseconds, and then successfully shuttled the information to a second qubit.
"We tested a new element for quantum information systems," says NIST physicist Ray Simmonds. "It's really significant because it means we can couple more qubits together and transfer information between them easily using one simple element."
The NIST work, together with another letter in the same issue of Nature by a Yale University group, is the first demonstration of a superconducting quantum bus. Whereas the NIST scientists used the bus to store and transfer information between independent qubits, the Yale group used it to enable an interaction of two qubits, creating a combined superposition state. These three actions, demonstrated collectively by the two groups, are essential for performing the basic functions needed in a superconductor-based quantum information processor of the future.
In addition to storing and transferring information, NIST's resonant cable also offers a means of "refreshing" superconducting qubits, which normally can maintain the same delicate quantum state for only half a microsecond. Disturbances such as electric or magnetic noise in the circuit can rapidly destroy a qubit's superposition state. With design improvements, the NIST technology might be used to repeatedly refresh the data and extend qubit lifetime more than 100-fold, sufficient to create a viable short-term quantum computer memory, Simmonds says. NIST's resonant cable might also be used to transfer quantum information between matter and light -- microwave energy is a low-frequency form of light -- and thus link quantum computers to ultra-secure quantum communications systems.
If they can be built, quantum computers -- harnessing the unusual rules of quantum mechanics, the principles governing nature's smallest particles -- might be used for applications such as fast and efficient code breaking, optimizing complex systems such as airline schedules, making counterfeit-proof money, and solving complex mathematical problems. Quantum information technology in general allows for custom-designed systems for fundamental tests of quantum physics and as-yet-unknown futuristic applications.
A superconducting qubit is about the width of a human hair. NIST researchers fabricate two qubits on a sapphire microchip, which sits in a shielded box about 8 cubic millimeters in size. The resonant section of cable is 7 millimeters long, similar to the coaxial wiring used in cable television but much thinner and flatter, zig-zagging around the 1.1 mm space between the two qubits. Like a guitar string, the resonant cable can be stimulated so that it hums or "resonates" at a particular tone or frequency in the microwave range. Quantum information is stored as energy in the form of microwave particles or photons.
The NIST research was supported in part by the Disruptive Technology Office.
*M.A. Sillanpää, J.I. Park, and R.W. Simmonds. 2007. Coherent quantum state storage and transfer between two phase qubits via a resonant cavity. Nature, Sept. 27.
Adapted from materials provided by National Institute of Standards and Technology.
New Plastic Is Strong As Steel, Transparent
By mimicking a brick-and-mortar molecular structure found in seashells, University of Michigan researchers created a composite plastic that's as strong as steel but lighter and transparent.
It's made of layers of clay nanosheets and a water-soluble polymer that shares chemistry with white glue.
Engineering professor Nicholas Kotov almost dubbed it "plastic steel," but the new material isn't quite stretchy enough to earn that name. Nevertheless, he says its further development could lead to lighter, stronger armor for soldiers or police and their vehicles. It could also be used in microelectromechanical devices, microfluidics, biomedical sensors and valves and unmanned aircraft.
Kotov and other U-M faculty members are authors of a paper on this composite material, "Ultrastrong and Stiff Layered Polymer Nanocomposites," published in the Oct. 5 edition of Science.
The scientists solved a problem that has confounded engineers and scientists for decades: Individual nano-size building blocks such as nanotubes, nanosheets and nanorods are ultrastrong. But larger materials made out of bonded nano-size building blocks were comparatively weak. Until now.
"When you tried to build something you can hold in your arms, scientists had difficulties transferring the strength of individual nanosheets or nanotubes to the entire material," Kotov said. "We've demonstrated that one can achieve almost ideal transfer of stress between nanosheets and a polymer matrix."
The researchers created this new composite plastic with a machine they developed that builds materials one nanoscale layer after another.
The robotic machine consists of an arm that hovers over a wheel of vials of different liquids. In this case, the arm held a piece of glass about the size of a stick of gum on which it built the new material.
The arm dipped the glass into the glue-like polymer solution and then into a liquid that was a dispersion of clay nanosheets. After those layers dried, the process repeated. It took 300 layers of each the glue-like polymer and the clay nanosheets to create a piece of this material as thick as a piece of plastic wrap.
Mother of pearl, the iridescent lining of mussel and oyster shells, is built layer-by-layer like this. It's one of the toughest natural mineral-based materials.
The glue-like polymer used in this experiment, which is polyvinyl alcohol, was as important as the layer-by-layer assembly process. The structure of the "nanoglue" and the clay nanosheets allowed the layers to form cooperative hydrogen bonds, which gives rise to what Kotov called "the Velcro effect." Such bonds, if broken, can reform easily in a new place.
The Velcro effect is one reason the material is so strong. Another is the arrangement of the nanosheets. They're stacked like bricks, in an alternating pattern.
"When you have a brick-and-mortar structure, any cracks are blunted by each interface," Kotov explained. "It's hard to replicate with nanoscale building blocks on a large scale, but that's what we've achieved."
Collaborators include: mechanical engineering professor Ellen Arruda; aerospace engineering professor Anthony Waas; chemical, materials science and biomedical engineering professor Joerg Lahann; and chemistry professor Ayyalusamy Ramamoorthy. Kotov is a professor of chemical engineering, materials science and engineering, and biomedical engineering.
The nanomechanical behavior of these materials is being modeled by professor Arruda's group; Waas and his group are working on applications in aviation.
Adapted from materials provided by University of Michigan.
It's made of layers of clay nanosheets and a water-soluble polymer that shares chemistry with white glue.
Engineering professor Nicholas Kotov almost dubbed it "plastic steel," but the new material isn't quite stretchy enough to earn that name. Nevertheless, he says its further development could lead to lighter, stronger armor for soldiers or police and their vehicles. It could also be used in microelectromechanical devices, microfluidics, biomedical sensors and valves and unmanned aircraft.
Kotov and other U-M faculty members are authors of a paper on this composite material, "Ultrastrong and Stiff Layered Polymer Nanocomposites," published in the Oct. 5 edition of Science.
The scientists solved a problem that has confounded engineers and scientists for decades: Individual nano-size building blocks such as nanotubes, nanosheets and nanorods are ultrastrong. But larger materials made out of bonded nano-size building blocks were comparatively weak. Until now.
"When you tried to build something you can hold in your arms, scientists had difficulties transferring the strength of individual nanosheets or nanotubes to the entire material," Kotov said. "We've demonstrated that one can achieve almost ideal transfer of stress between nanosheets and a polymer matrix."
The researchers created this new composite plastic with a machine they developed that builds materials one nanoscale layer after another.
The robotic machine consists of an arm that hovers over a wheel of vials of different liquids. In this case, the arm held a piece of glass about the size of a stick of gum on which it built the new material.
The arm dipped the glass into the glue-like polymer solution and then into a liquid that was a dispersion of clay nanosheets. After those layers dried, the process repeated. It took 300 layers of each the glue-like polymer and the clay nanosheets to create a piece of this material as thick as a piece of plastic wrap.
Mother of pearl, the iridescent lining of mussel and oyster shells, is built layer-by-layer like this. It's one of the toughest natural mineral-based materials.
The glue-like polymer used in this experiment, which is polyvinyl alcohol, was as important as the layer-by-layer assembly process. The structure of the "nanoglue" and the clay nanosheets allowed the layers to form cooperative hydrogen bonds, which gives rise to what Kotov called "the Velcro effect." Such bonds, if broken, can reform easily in a new place.
The Velcro effect is one reason the material is so strong. Another is the arrangement of the nanosheets. They're stacked like bricks, in an alternating pattern.
"When you have a brick-and-mortar structure, any cracks are blunted by each interface," Kotov explained. "It's hard to replicate with nanoscale building blocks on a large scale, but that's what we've achieved."
Collaborators include: mechanical engineering professor Ellen Arruda; aerospace engineering professor Anthony Waas; chemical, materials science and biomedical engineering professor Joerg Lahann; and chemistry professor Ayyalusamy Ramamoorthy. Kotov is a professor of chemical engineering, materials science and engineering, and biomedical engineering.
The nanomechanical behavior of these materials is being modeled by professor Arruda's group; Waas and his group are working on applications in aviation.
Adapted from materials provided by University of Michigan.
Stopping Atoms
With atoms and molecules in a gas moving at thousands of kilometres per hour, physicists have long sought a way to slow them down to a few kilometres per hour to trap them.
A paper, published October 4 in the Institute of Physics' New Journal of Physics, demonstrates how a group of physicists from The University of Texas at Austin, US, have found a way to slow down, stop and explore a much wider range of atoms than ever before.
Inspired by the coilgun that was developed by the University's Center for Electromechanics, the group has developed an "atomic coilgun" that slows and gradually stops atoms with a sequence of pulsed magnetic fields.
Dr. Mark Raizen and his colleagues in Texas ultimately plan on using the gun to trap atomic hydrogen, which he said has been the Rosetta Stone of physics for many years and is the simplest and most abundant atom in the universe.
Work on slowing and stopping atoms has been at the forefront of advancement in physics for some time. In 1997, there were three joint-winners for the Nobel Prize in Physics for their combined contribution to laser cooling - a method using laser light to cool gases and keep atoms floating or captured in "atom traps".
These important advances had limited use because they only applied to atoms with 'closed two-level transition', excluding important elements such as hydrogen, iron, nickel and cobalt. In contrast, nearly all elements and a wide range of molecules are affected by magnetic forces, or are paramagnetic, which means that this latest research has much wider applicability.
Professor Raizen said, "Of particular importance are the doors being opened for our understanding of hydrogen. Precision spectroscopy of hydrogen's isotopes, deuterium and tritium, continues to be of great interest to both atomic and nuclear physics. Further study of tritium, as the simplest radioactive element, also serves as an ideal system for the study of Beta decay. "
Having successfully designed and used an 18-coil device to slow a supersonic beam of metastable neon atoms, the team is now developing a 64-stage device to further slow and stop atoms.
Adapted from materials provided by Institute of Physics.
A paper, published October 4 in the Institute of Physics' New Journal of Physics, demonstrates how a group of physicists from The University of Texas at Austin, US, have found a way to slow down, stop and explore a much wider range of atoms than ever before.
Inspired by the coilgun that was developed by the University's Center for Electromechanics, the group has developed an "atomic coilgun" that slows and gradually stops atoms with a sequence of pulsed magnetic fields.
Dr. Mark Raizen and his colleagues in Texas ultimately plan on using the gun to trap atomic hydrogen, which he said has been the Rosetta Stone of physics for many years and is the simplest and most abundant atom in the universe.
Work on slowing and stopping atoms has been at the forefront of advancement in physics for some time. In 1997, there were three joint-winners for the Nobel Prize in Physics for their combined contribution to laser cooling - a method using laser light to cool gases and keep atoms floating or captured in "atom traps".
These important advances had limited use because they only applied to atoms with 'closed two-level transition', excluding important elements such as hydrogen, iron, nickel and cobalt. In contrast, nearly all elements and a wide range of molecules are affected by magnetic forces, or are paramagnetic, which means that this latest research has much wider applicability.
Professor Raizen said, "Of particular importance are the doors being opened for our understanding of hydrogen. Precision spectroscopy of hydrogen's isotopes, deuterium and tritium, continues to be of great interest to both atomic and nuclear physics. Further study of tritium, as the simplest radioactive element, also serves as an ideal system for the study of Beta decay. "
Having successfully designed and used an 18-coil device to slow a supersonic beam of metastable neon atoms, the team is now developing a 64-stage device to further slow and stop atoms.
Adapted from materials provided by Institute of Physics.
What Makes Quantum Dots Blink?
In order to learn more about the origins of quantum dot blinking, researchers from the U.S. Department of Energy's Argonne National Laboratory, the University of Chicago and the California Institute of Technology have developed a method to characterize it on faster time scales than have previously been accessed.
Nanocrystals of semiconductor material, also known as quantum dots, are being intensively investigated for applications such as light-emitting diodes, solid-state lighting, lasers, and solar cells. They are also already being applied as fluorescent labels for biological imaging, providing several advantages over the molecular dyes typically used, including a wider range of emitted colors and much greater stability.
Quantum dots have great promise as light-emitting materials, because the wavelength, or color, of light that the quantum dots give off can be very widely tuned simply by changing the size of the nanoparticles. If a single dot is observed under a microscope, it can be seen to randomly switch between bright and dark states.
This flickering, or blinking, behavior has been widely studied, and it has been found that a single dot can blink off for times that can vary between microseconds and several minutes. The causes of the blinking, though, remain the subject of intense study.
The methods developed by Matt Pelton of Argonne's Center for Nanoscale Materials and his team of collaborators has revealed a previously unobserved change in the blinking behavior on time scales less than a few microseconds. This observation is consistent with the predictions of a model for quantum-dot blinking previously developed by Nobel Laureate Rudolph Marcus, contributor to this research, and his co-workers. In this model, the blinking is controlled by the random fluctuation of energy levels in the quantum dot relative to the energies of trap states on the surface of the nanocrystal or in the nearby environment.
The results of this research provide new insight into the mechanism of quantum-dot blinking, and should help in the development of methods to control and suppress blinking. Detailed results of this work have been published in a paper in the Proceedings of the National Academy of Sciences.
Argonne's Center for Nanoscale Materials work for this research was funded by the U.S. Department of Energy's Office of Basic Energy Science.
Adapted from materials provided by DOE/Argonne National Laboratory.
Nanocrystals of semiconductor material, also known as quantum dots, are being intensively investigated for applications such as light-emitting diodes, solid-state lighting, lasers, and solar cells. They are also already being applied as fluorescent labels for biological imaging, providing several advantages over the molecular dyes typically used, including a wider range of emitted colors and much greater stability.
Quantum dots have great promise as light-emitting materials, because the wavelength, or color, of light that the quantum dots give off can be very widely tuned simply by changing the size of the nanoparticles. If a single dot is observed under a microscope, it can be seen to randomly switch between bright and dark states.
This flickering, or blinking, behavior has been widely studied, and it has been found that a single dot can blink off for times that can vary between microseconds and several minutes. The causes of the blinking, though, remain the subject of intense study.
The methods developed by Matt Pelton of Argonne's Center for Nanoscale Materials and his team of collaborators has revealed a previously unobserved change in the blinking behavior on time scales less than a few microseconds. This observation is consistent with the predictions of a model for quantum-dot blinking previously developed by Nobel Laureate Rudolph Marcus, contributor to this research, and his co-workers. In this model, the blinking is controlled by the random fluctuation of energy levels in the quantum dot relative to the energies of trap states on the surface of the nanocrystal or in the nearby environment.
The results of this research provide new insight into the mechanism of quantum-dot blinking, and should help in the development of methods to control and suppress blinking. Detailed results of this work have been published in a paper in the Proceedings of the National Academy of Sciences.
Argonne's Center for Nanoscale Materials work for this research was funded by the U.S. Department of Energy's Office of Basic Energy Science.
Adapted from materials provided by DOE/Argonne National Laboratory.
New Path For Designing Novel Nanomaterials Discovered
A University of Arkansas researcher and his colleagues have found a novel way to “look” at atomic orbitals, and have directly shown for the first time that they change substantially when interacting at the interface of a ferromagnet and a high-temperature superconductor.
This finding opens up a new way of designing nanoscale superconducting materials and fundamentally changes scientific convention, which suggests that only electron spin and atomic charge – not atomic orbitals – influence the properties of superconducting nanostructures. It also has implications for interfaces between other complex oxide materials.
Jacques Chakhalian, assistant professor of physics in the J. William Fulbright College of Arts and Sciences, and his colleagues will publish their findings online at the Science Express Web site, published by the journal Science, Oct. 11.
Until now, materials science researchers believed that an electron’s charge and spin influenced the characteristics of conventional bulk materials. Atomic orbitals, which consist of the patterns of electron density that may be formed in an atom, were previously thought to be inactive.
“In conventional materials like copper or silicon, you could account for everything you could see through charge and spin,” Chakhalian said. Further, orbitals have proved difficult to “see” through physical experimentation, so it wasn’t possible to examine any changes in orbital symmetry that might be taking place at the interface.
Chakhalian’s work has focused on what happens at the interface between two different materials – for instance, superconductors and ferromagnets, two materials with properties that were thought to be incompatible with each other in bulk. In 2006, he and his colleagues created the first high-quality material to have both superconducting and ferromagnetic properties, and they used that material in this experiment.
Chakhalian and his colleagues worked with synchrotron radiation at the Advanced Photon Source, Argonne National Laboratory in Argonne, Ill., to examine the interface between a high-temperature superconducting material containing copper oxide and a ferromagnetic material containing manganese oxide. The synchrotron light is electromagnetic radiation of varying wavelengths that can be tuned to a specific wavelength and polarization for a particular experiment. Unlike conventional X-rays, which diffuse through space, the synchrotron light beams are sharply focused, like a laser beam with extreme brilliance.
The researchers forced the two materials into unusual quantum states. Using a technique called resonant X-ray absorption, they were able to “look” at the atomic orbitals at the interface and determine their symmetry in a non-destructive way.
They found that the atomic orbitals changed the nature of their symmetry at the interface and created a covalent bond between the copper and manganese atoms. This bonding does not exist in the bulk of the individual materials
“When you merge these two materials, the atomic orbitals at the interface become important. They start contributing to the electronic properties of the material,” Chakhalian said. “This opens a new way of designing materials. We can design quantum materials with engineered physical properties.”
The discovery may allow researchers to manipulate nanoscale superconductivity at the interface – opening the possibility of creating room-temperature semiconductors.
Generators that use superconducting materials generate electricity extremely efficiently, at half the size of conventional generators. General Electric estimates the potential market for superconducting generators to be between billion and billion over the next decade.
Chakhalian’s colleagues include J.W. Freeland and M. van Veenendaal of the Advanced Photon Source, Argonne National Laboratory, Argonne, Ill.; and H.-U. Habermeier, G. Cristiani, G. Khaliullin and B. Keimer of the Max Planck Institute for Solid State Research in Stuttgart, Germany.
Adapted from materials provided by University of Arkansas, Fayetteville.
This finding opens up a new way of designing nanoscale superconducting materials and fundamentally changes scientific convention, which suggests that only electron spin and atomic charge – not atomic orbitals – influence the properties of superconducting nanostructures. It also has implications for interfaces between other complex oxide materials.
Jacques Chakhalian, assistant professor of physics in the J. William Fulbright College of Arts and Sciences, and his colleagues will publish their findings online at the Science Express Web site, published by the journal Science, Oct. 11.
Until now, materials science researchers believed that an electron’s charge and spin influenced the characteristics of conventional bulk materials. Atomic orbitals, which consist of the patterns of electron density that may be formed in an atom, were previously thought to be inactive.
“In conventional materials like copper or silicon, you could account for everything you could see through charge and spin,” Chakhalian said. Further, orbitals have proved difficult to “see” through physical experimentation, so it wasn’t possible to examine any changes in orbital symmetry that might be taking place at the interface.
Chakhalian’s work has focused on what happens at the interface between two different materials – for instance, superconductors and ferromagnets, two materials with properties that were thought to be incompatible with each other in bulk. In 2006, he and his colleagues created the first high-quality material to have both superconducting and ferromagnetic properties, and they used that material in this experiment.
Chakhalian and his colleagues worked with synchrotron radiation at the Advanced Photon Source, Argonne National Laboratory in Argonne, Ill., to examine the interface between a high-temperature superconducting material containing copper oxide and a ferromagnetic material containing manganese oxide. The synchrotron light is electromagnetic radiation of varying wavelengths that can be tuned to a specific wavelength and polarization for a particular experiment. Unlike conventional X-rays, which diffuse through space, the synchrotron light beams are sharply focused, like a laser beam with extreme brilliance.
The researchers forced the two materials into unusual quantum states. Using a technique called resonant X-ray absorption, they were able to “look” at the atomic orbitals at the interface and determine their symmetry in a non-destructive way.
They found that the atomic orbitals changed the nature of their symmetry at the interface and created a covalent bond between the copper and manganese atoms. This bonding does not exist in the bulk of the individual materials
“When you merge these two materials, the atomic orbitals at the interface become important. They start contributing to the electronic properties of the material,” Chakhalian said. “This opens a new way of designing materials. We can design quantum materials with engineered physical properties.”
The discovery may allow researchers to manipulate nanoscale superconductivity at the interface – opening the possibility of creating room-temperature semiconductors.
Generators that use superconducting materials generate electricity extremely efficiently, at half the size of conventional generators. General Electric estimates the potential market for superconducting generators to be between billion and billion over the next decade.
Chakhalian’s colleagues include J.W. Freeland and M. van Veenendaal of the Advanced Photon Source, Argonne National Laboratory, Argonne, Ill.; and H.-U. Habermeier, G. Cristiani, G. Khaliullin and B. Keimer of the Max Planck Institute for Solid State Research in Stuttgart, Germany.
Adapted from materials provided by University of Arkansas, Fayetteville.
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