You are here

Highlights

  • 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. The building blocks, known as split ring resonators, are...

    Read More
  • A new ultra-fast laser technique has yielded insights into how iron arsenide materials evolve to form a superconducting state. This transformation involves complex changes in magnetism, structural order, and electronic order that appear to be going on simultaneously — not simply competing with each other.  Only by looking at very fast time scales (10 thousandths of a billionth of a second) and using the highest quality single crystals could these transformational changes be separated and analyzed; ultra-fast spectroscopy enabled scientists to study the superconducting transformation...

    Read More
  • 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. Interestingly, the...

    Read More
  • 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. Indeed, graphene provides a number of advantages over metals including that its properties offer the unprecedented ability to tune the electrical response for a...

    Read More
  • 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. By contrast, in cuprate...

    Read More
  • 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. Thus, Homes scaling can be considered...

    Read More
  • Scientists have discovered that the rare earth element dysprosium grown on graphene — a one atom thick layer of carbon — forms triangular-shaped islands, whereas other magnetic metals form hexagonal-shaped islands. Based on the hexagonal closed packed (hcp) bulk crystal structure of dysprosium, hexagonal islands would also have been expected. Researchers used scanning tunneling microscopy to identify the crystal structure of dysprosium on graphene. The results indicate that dysprosium grows as face centered cubic (fcc) crystals on graphene rather than hcp. The triangular shape arises, in...

    Read More
  • Scientists have discovered a fascinating secret about praseodymium aluminide. When PrAl2 is cooled, its crystal structure changes from high symmetry cubic to low symmetry tetragonal below -400 °F (32 K). However, when the cooling is done in a high magnetic field, the material retains the cubic structure. This change is not observed in other rare-earth aluminides. Furthermore, PrAl2 has an anomalous heat capacity per unit mass at low temperatures.  It is 10x higher than pure praseodymium. (Heat capacity is the amount of heat needed to raise the temperature of a...

    Read More
  • For the first time, researchers can now both explain and predict the behavior of different materials while they are being pulled apart.  Some materials are ductile, meaning they will deform without losing their toughness, and others are brittle.  The results explain even the unexpected and anomalous ductility of a material within a class of rare-earth-containing materials that are otherwise known to be brittle.  To predict the behavior requires two maps.  The first map...

    Read More
  • A study of thermoelectrics, materials that convert heat to electricity, demonstrates the importance of characterizing materials using several different methods. According to Vegard’s Law of Alloys, the size of a crystalline lattice (lattice parameter) changes linearly with composition. It is actually not a law, but an empirical observation that has been found to hold true for a majority of alloys. Researchers studied thermoelectrics made from lead, tellurium, and sulfur and varied the tellurium and sulfur content to answer the question “If a thermoelectric follows Vegard’s Law, does that...

    Read More

Pages