June 2007 Archives

Electromagnetically induced transparency (EIT) is a coherent optical nonlinearity, and brings dramatic changes in optical properties such as absorption, emission, refraction etc. The phenomena relate to the quantum mechanical overlapping state created by two different wavelengths of coherent light. Recently, EIT for X-rays has been theoretically predicted. According to the theory, it is possible to make Ne gas, which is normally opaque, transparent by exposing it to laser light of 800 nm with extremely high flux of 10¹² W/cm². The scheme could be used for producing ultra-short X-ray pulses. For more information, see the paper, "Electromagnetically Induced Transparency for X Rays ", C. Buth et al., Phys. Rev. Lett., 98, 253001 (2007). For more about general EIT, see, for example, "Electromagnetically Induced Transparency.", S. Harris, Physics Today, 50, 36-42 (1997).

Scientists at Argonne National Laboratory and Ames Laboratory, Iowa State University, have recently performed X-ray magnetic circular dichroism (XMCD) measurements of giant magnetocaloric material, Gd₅(Ge_1-xSi_x)₄. It was found that germanium becomes magnetic by spin-dependent hybridization between Ge 4p and Gd 5d. This hybridization can change at the germanium-silicon bond-breaking transition, causing the destruction of magnetic ordering and leading to the giant magnetocaloric effect. By combining the experimental results with calculations based on density functional theory, it was concluded that the magnetized germanium orbitals act as "magnetic bridges" in mediating the magnetic interactions across the distant gadolinium ions. For more information, see the paper, "Role of Ge in Bridging Ferromagnetism in the Giant Magnetocaloric Gd₅(Ge_1-xSi_x)₄ Alloys", D. Haskel et al., Phys. Rev. Lett., 98, 247205 (2007).