Transparent, Unipolar, QD-Based LEDs Operate in Air
- PDF / 53,635 Bytes
- 1 Pages / 576 x 783 pts Page_size
- 12 Downloads / 166 Views
Quantum Critical Point Found for Iron Arsenide Superconductors New experiments on a recently discovered class of iron-based superconductors suggest that the ability of their electrons to conduct electricity without resistance is directly connected with the magnetic properties of those electrons. Results of the experiments appear in the January 8 issue of Physical Review Letters (DOI: 10.1103/PhysRevLett.104. 017204). The tests, which were carried out by a team of U.S. and Chinese researchers, shed light on the fundamental nature of high-temperature superconductivity, said Rice University researcher Qimiao Si, a co-author on the study. If better understood, high-temperature superconductors could be used to revolutionize electric generators, MRI scanners, high-speed trains, and other devices. In the study, researchers from Rice University, the University of Tennessee, Oak Ridge National Laboratory (ORNL), the National Institute of Standards and Technology (NIST), the Chinese Academy of Sciences’ Institute of Physics, and Renmin University in Beijing examined several ironarsenide compounds. These are the undoped parents of the iron pnictides, a class
Transparent, Unipolar, QD-Based LEDs Operate in Air Due to their high efficiencies and tunable band emission, quantum dots (QDs) have great potential for being the active layer in light-emitting devices for many applications including solid-state lighting and advanced display technologies. The current challenges involved with using quantum dots in lightemitting devices are achieving device stability and aligning energy bands between charge transport layers and QD emitters. V. Wood, V. Bulovic, M.G. Bawendi, and colleagues at the Massachusetts Institute of Tech no l ogy have recently created allinorganic, unipolar, QD-based light-emitting devices (QD-LEDs). The device design simplifies energy band alignment by using only electrons as the charge carrier type while also being able to operate in air even un-
The Leader in Vacuum Valves
www.vatvalve.com 176
of materials that were found to be hightemperature superconductors in 2008. The experiments set out to test theoretical predictions that Si and collaborators published in the Proceedings of the National Academy of Sciences last year. They predicted that varying the size of some atoms in the parent compounds could allow researchers to tune the material’s quantum fluctuations. These types of fluctuations can create tipping points called magnetic “quantum critical points,” a state that exists when a material is at the cusp of transitioning from one quantum phase to another. Using neutron-scattering facilities at NIST and ORNL, the team bombarded the materials with neutrons to decipher their structural and magnetic properties. The tests, which supported Si’s theoretical predictions, determined that the strength of magnetic order in the materials was reduced when arsenic atoms were replaced with slightly smaller phosphorus atoms. “We found the first direct evidence that a magnetic quantum critical point exists in these mater
Data Loading...
