Stanford University researchers working in part at SSRL have discovered a novel set of properties pertaining to a compound of materials called tritellurides. These compounds, composed of three atoms of tellurium and a single atom of one of the rare earth elements, demonstrate unique electronic properties that can be controlled by altering the temperature of the material.

The tritellurides display phenomena known as charge density waves (CDW). In a normal conductive metal, electrons persist in a "sea" wherein they are evenly distributed and equally available, or conductive. A CDW occurs under certain circumstances and causes the electrons to clump together, lowering their availability, and thereby lowering the compound's conductivity. Tellurium, when crystallized into quasi-two-dimensional planes and combined with rare earth elements, produces a material with CDWs that can be manipulated and controlled.

Using electrical conductance tests at Stanford and x-ray diffraction measurements at SSRL Beam Lines 11-3 and 7-2, the group found that, when tellurium is combined with rare earth elements - in this case erbium and terbium - the CDW can be induced by manipulating the temperature of the compound. This "threshold temperature" is different for each rare earth element, and in some cases is room temperature. In the case of erbium, the group found that the compound actually has two threshold temperatures, which induce CDWs that occur at 90 degrees to one another. These results could reveal clues to how superconductors, which can also demonstrate CDWs, could be further exploited to create novel materials with unique electronic properties.

N. Ru, C.L. Condron, G.Y. Margulis, K.Y. Shin, J. Laverock, S.B. Dugdale, M.F. Toney, I.R. Fisher, Phys Rev. B 77, 035114 (2008)

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/cdw_compounds.html