{"id":1797,"date":"2016-07-25T05:39:00","date_gmt":"2016-07-25T05:39:00","guid":{"rendered":"http:\/\/198.74.50.173\/2016\/07\/newly-discovered-material-property-may.html"},"modified":"2017-04-07T03:13:37","modified_gmt":"2017-04-07T03:13:37","slug":"newly-discovered-material-property-may","status":"publish","type":"post","link":"https:\/\/www.nextbigfuture.com\/2016\/07\/newly-discovered-material-property-may.html","title":{"rendered":"Newly discovered material property may lead to high temp superconductivity"},"content":{"rendered":"
Researchers at the U.S. Department of Energy\u2019s (DOE) Ames Laboratory have discovered an unusual property of purple bronze that may point to new ways to achieve high<\/a> temperature superconductivity.<\/p>\n While studying purple bronze, a molybdenum oxide, researchers discovered an unconventional charge density wave on its surface.<\/p>\n A charge density wave (CDW) is a state of matter where electrons bunch together in a repeating pattern, like a standing wave of surface of water. Superconductivity and charge density waves share a common origin, often co-exist, and can compete for dominance in certain materials.<\/p>\n Conventional CDWs and superconductivity both arise from electron-phonon interactions, the interaction of electrons with the vibrations of the crystal lattice. Electron-electron interactions are the likely origin of unconventional, high-temperature superconductivity such as found in copper- and iron-based compounds.<\/p>\n Unconventional, electron-electron driven CDW are extremely rare and its discovery here is important, because the material showed an \u2018extraordinary\u2019 increase of CDW transition temperature from 130K (-143\u00b0C) to 220K (-53 \u00b0C) and a huge increase of energy gap at the surface.<\/p>\n \nBulk and surface CDW transition. (a) High-energy x-ray diffraction patterns of the reciprocal lattice plane ( H\u2009K\u20090 ). The CDW superstructure peaks are marked by blue arrows (logarithmic color scale). (b) High-resolution diffraction patterns of the ( 92 0 0) CDW peak (linear color scale). (c) Plot of the temperature dependence of the CDW peak (linear color scale). The intensity is obtained by summing up the high-resolution diffraction patterns of the ( 92 0 0) peak along the transverse direction in (b), and is plotted along the longitudinal direction. (d) LEED images. Red arrows point to CDW superstructure peaks.<\/i><\/p>\n \nSummary of the temperature-dependent CDW gap and band structure evolvement. (a) Temperature dependence of the surface (red solid circles) and bulk (blue solid circles) CDW gap. The surface gap is extracted from the back bending point of the surface band and the bulk gap is extracted from the leading edge shift of kF EDCs [Fig. 1]. The gray solid line is a BCS-like temperature dependence with \u03940=12\u2009\u2009meV . The integrated intensity of the CDW peak measured by x-ray diffraction [Fig. 2] is shown with yellow solid circles. Black data points represent the intensity of CDW peaks measured by LEED. Dashed line is a guide to the eye. (b) Illustration of the surface (blue line) and bulk (red line) band dispersion. (c) Illustration of surface (red) and bulk (blue) CDW formation in real space. Dashed lines represent a density distribution of conducting electrons.<\/i><\/p>\n \nBulk and surface CDW gaps: (a) Measured FS at 130 K. Intensity is integrated within EF\u00b110\u2009\u2009meV and data are symmetrized with sixfold symmetry. Dashed arrows indicate three nesting vectors, each connecting two quasi-1D FS sheets [51]. The red rectangle is expanded in the left-bottom inset to demonstrate the FS hybridization. (b)\u2013(d) ARPES intensity measured along the cut (red line) shown in (a). (e) Extracted band dispersion from (d). (f) EDCs along the same cut. (g)\u2013(i) ARPES intensity divided by Fermi function close to EF at 130, 75, and 45 K. (j) Temperature dependence of the EDCs at kF showing opening of bulk CDW gap. (k) Same as in (j), but symmetrized about EF .<\/i><\/p>\n Physics Review Letters – Discovery of an Unconventional Charge Density Wave at the Surface of K0.9Mo6O17<\/a><\/p>\n