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BCS Theory of Superconductivity Explains Universal Behavior

A recent discovery suggested to be a universal behavior of superconductors does not require a fancy new explanation; it elegantly falls out from the BCS theory of superconductivity, first published in 1957.The universal behavior is scaling relationship, known as Homes scaling, that relates the penetration depth of the magnetic field to the superconducting transition temperature and conductivity. It is valid over many orders of magnitude from the so-called “dirty”, short mean-free path, superconductors up to as clean materials as one can synthesize.

Neutron Spin Resonance in Iron-based Superconductors

The propagation of a novel magnetic excitation in the superconducting state, called a spin resonance, has been observed in iron arsenide superconductors for the first time. How the resonance disperses depends upon the direction probed within the single crystals studied. Propagation of the spin resonance reveals details about the superconducting state and highlights qualitative differences between iron arsenide and cuprate superconducting materials. The magnetic excitation appears in the superconducting state with upwards dispersion in iron arsenide superconductors.

Carbon Layers Lead the Way towards a New Generation of Metamaterials

Graphene — a one layer thick sheet of carbon atoms — has special properties that make it a desirable material for manipulating terahertz waves. Terahertz applications operate at frequencies between microwave and far infrared. Some metamaterials, which are engineered structures that can manipulate light in ways not seen in conventional materials, could benefit by replacing the metals currently used to build them with graphene.

Too Crowded to Exit!

Crowding controls whether carbon chains or a hydrogen atom will transfer from transition metal molecular complexes to acceptor molecules. To gain this new insight into the factors governing the onset of hydrogen abstraction from metal alkyls, researchers carefully designed experiments involving series of cobalt and chromium alkyls.  The results show that when the alkyl chain is only one carbon long, the alkyl group will transfer to a rhodium acceptor molecule.  But, if the chain is made up of two or more carbons, crowding makes it hard for the alkyl group to transfer.

New Magnetic Structure Discovered

A new metallic material — based on the substitution of manganese for iron in an iron–arsenide superconductor — has been discovered in which the microscopic magnets of the electron current carriers provided by the potassium atoms all line up in the same direction at low temperatures whereas the neighboring microscopic magnets of the manganese atoms line up in opposite directions to each other. This material, Ba0.6K0.4Mn2As2, thus exhibits a novel magnetic behavior with ferromagnetic and antiferromagnetic behavior coexisting.

Novel Broadband Terahertz Light Emitters

Broadband terahertz light emitters have been designed and fabricated using nanoscale U-shaped building blocks. The terahertz spectral range sits between infrared and typical radar frequencies, and the challenges of efficiently generating and detecting terahertz radiation has limited its use. However, broadband terahertz sources offer exciting possibilities to study fundamental physics principles, to develop non-invasive material imaging and sensing, and make possible terahertz information, communication, processing and storage.

Tricking Iron into Acting like a Rare-earth Element

By slipping iron between two nitrogen atoms in a lithium matrix, researchers are able to trick iron into having magnetic properties like those of rare-earth elements.Rare-earth magnets are stronger than typical iron-based magnets and have high magnetic anisotropy, meaning they are easily magnetized in one particular direction.  Rare-earth elements are in high demand, difficult to find in large concentrations, and costly to mine.  Iron, in contrast, is abundant and cheap.  If iron can be made to behave like a rare-earth element, strong permanent magnets could be made without rare earths.  I


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