Inverse photoemission spectra of a decagonal single quasicrystal Al72Ni12Co16

Abstract

The extremely large electrical resistivity of Quasicrystal (QC) consisting of only metallic element has been discussed to be originated from a pseudo-gap in the vicinity of the Fermi level and spiky structure of the density of states (DOS) in the QC. The inverse photoemission spectra (IPES) of the two-dimensional decagonal Al-Ni-Co single QC have been studied to investigate its electronic structure, where quasiperiodic planes are stacked along a c-axis in a normal crystalline periodicity. Anisotropic transport properties in the decagonal QC have been observed in accordance with the structural anisotropy. The conditions for the measurement of the IPES of the QC are described. And, the specimens used in the study were Al72Ni12Co16 single QC grown by the Czochralski method. The IPES of Al72Ni12Co16 and gold obtained for incident electron energy of 66.3 eV were shown in a figure. The metallic edge was recognized in the IPES of gold, however, the IPES of Al72Ni12Co16 showed no clear Fermi edge and its intensity increased towards the low binding energy. It was suggested that the intensity of IPES of Al72Ni12Co16 was low in the vicinity of the Fermi level, and hence that there existed an opening of the pseudo-gap in the decagonal QC.

金属元素だけから成る準結晶(QC)の比電気抵抗が極めて大きいことを、QC内のフェルミ準位近傍の擬ギャップおよび状態密度(DOS)のスパイク状構造が原因であると論じた。QCの電子構造を検討するために、準周期面が正規結晶周期性状態のc軸に沿って積層されている2次元10角形Al-Ni-Co単結晶準結晶の逆光電子放出スペクトル(IPES)を研究した。構造的異方性に合致する異方的輸送特性を10角形QC内に観測した。QCのIPES測定条件を記述した。また、研究で用いた試験片はチョクラルスキー法により成長させたAl72Ni12Co16単結晶準結晶を用いた。66.3eVの入射電子エネルギーに対して求めたAl72Ni12Co16と金のIPESを図に示した。金のIPESには金属端を認めたが、Al72Ni12Co16のIPESは明確なフェルミ端を示さず、スペクトルの強さは低結合エネルギーに向かって増加した。Al72Ni12Co16のIPESの強さはフェルミ準位の近傍では弱く、そのため、10角形QC内には擬ギャップの開口部が存在することを示唆している。