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Topic Name: Researchers now one step closer to getting a grip on superconductivity at high temperatures
Category: Nuclear Magnetic Resonance
Research persons: Andrea D. Bianchi
Location: Université de Montréal, Canada
Details
An international research team has discovered that a magnetic field can interact with the electrons in a superconductor in ways never before observed.
Andrea D.
Bianchi, the lead researcher from the Université de Montréal, explains in the January 11 edition of Science magazine what he discovered in an exceptional compound of metals – a combination of cobalt, indium and a rare earth – that loses its resistance when cooled to just a couple of degrees above absolute zero.
“This discovery sharpens our understanding of what, literally, holds the world together and brings physicists one step closer to getting a grip on superconductivity at high temperatures. Until now, physicists were going around in circles, so this discovery will help to drive new understanding,” said Prof. Bianchi, who was recruited to UdeM as a Canada Research Chair in Novel Materials for Spintronics last fall and performed his experiments at the
Paul Scherrer Institute in Switzerland, in collaboration with scientists from ETH Zurich, the
University of Notre Dame, the University of Birmingham,
U.K., the Los Alamos National Laboratory and the
Brookhaven National
Laboratory.
Magnetic Tornado that grows stronger
Using the Swiss Spallation Neutron Source (SINQ), Prof. Bianchi and his team cooled a single-crystal sample of CeCoIn5 down to 50mK above absolute zero and applied a magnetic field nearly high enough to entirely suppress superconductivity. They found that the core of the vortices feature electronic spins that are partly aligned with the magnetic field. This is the first experimental evidence that a theory that describes the properties of superconducting vortices and, for which Abrikosov and Ginzburg received the Nobel Prize in 2003, which does not generally apply in magnetically-induced superconductors.
“When subjected to intense magnetic fields, these materials produce a completely new type of magnetic tornado that grows stronger with increasing fields rather than weakening,” said Prof. Bianchi. “The beauty of this compound is how we can experiment without breaking it.”
Superconductors hold great promise for technological applications that will change how modern civilization can store and transmit energy - arguably some of the most pressing challenges today. Other notable applications include superconducting digital filters for high-speed communications, more efficient and reliable generators and motors, and superconducting device applications in medical magnetic resonance imaging machines. The first superconductor was discovered nearly a hundred years ago, and in most materials this curious state with no resistance was shown to arise from the interaction of the electrons with the crystal; however, in this new material, superconductivity is thought to arise from magnetic interactions between electrons.
Note for Superconductivity
Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field (the Meissner effect).
The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Even near absolute zero a real sample of copper shows a non-zero resistance. The resistance of a superconductor, on the other hand, drops abruptly to zero when the material is cooled below its "critical temperature". An electrical current flowing in a loop of superconducting wire can persist indefinitely with no power source. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It cannot be understood simply as the idealization of "perfect conductivity" in classical physics. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys and some heavily-doped semiconductors. Superconductivity does not occur in noble metals like gold and silver, nor in most ferromagnetic metals.
Note for Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is primarily used in medical imaging to visualize the structure and function of the body. It provides detailed images of the body in any plane. MR has much greater soft tissue contrast than CT making it especially useful in neurological, musculoskeletal, cardiovascular and oncolological diseases. Unlike CT it uses no ionizing radiation. The scanner creates a powerful magnetic field which aligns the magnetization of hydrogen atoms in the body. Radio waves are used to alter the alignment of this magnetization. This causes the hydrogen atoms to emit a weak radio signal which is amplified by the scanner. This signal can be manipulated by additional magnetic fields to build up enough information to reconstruct an image of the body.
Magnetic resonance spectroscopy is used to measure the levels of different metabolites in body tissues. The MR signal produces spectrum of difference resonances that correspond to different molecular arrangements of the isotope being "excited". This signature is used to diagnose certain metabolic disorders, especially those affecting the brain, as well as to provide information on tumor metabolism.
In figure 2, A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. Persistent electric current flows on the surface of the superconductor, acting to exclude the magnetic field of the magnet (the Meissner effect). This current effectively forms an electromagnet that repels the magnet.
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