Matsui T, Kambara H, Niimi Y, Tagami K, Tsukada M, Fukuyama Hiroshi
Department of Physics, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Phys Rev Lett. 2005 Jun 10;94(22):226403. doi: 10.1103/PhysRevLett.94.226403. Epub 2005 Jun 7.
Scanning tunneling spectroscopy (STS) measurements were made on surfaces of two different kinds of graphite samples, Kish graphite and highly oriented pyrolytic graphite (HOPG), at very low temperatures and in high magnetic fields. We observed a series of peaks in the tunnel spectra associated with Landau quantization of the quasi-two-dimensional electrons and holes. A comparison with the calculated local density of states at the surface layers allows us to identify Kish graphite as bulk graphite and HOPG as graphite with a finite thickness of 40 layers. This explains the qualitative difference between the two graphites reported in the recent transport measurements which suggested the quantum-Hall effect in HOPG. This work demonstrates how powerful the combined approach between the high quality STS measurement and the first-principles calculation is in material science.
在极低温度和强磁场条件下，对两种不同类型的石墨样品——微晶石墨和高度取向热解石墨（HOPG）的表面进行了扫描隧道谱（STS）测量。我们在隧道谱中观察到了一系列与准二维电子和空穴的朗道量子化相关的峰。通过与表面层计算出的局域态密度进行比较，我们能够将微晶石墨识别为块状石墨，将HOPG识别为具有40层有限厚度的石墨。这解释了近期输运测量中报道的两种石墨之间的定性差异，该差异表明HOPG中存在量子霍尔效应。这项工作展示了高质量STS测量与第一性原理计算相结合的方法在材料科学中是多么强大。
