Invited Paper TF+NM-MoE1
Low-Dimensional Electronic System on Metal-Adsorbed Germanium Surfaces

Monday, December 8, 2014, 5:40 pm, Room Lehua

The electronic properties of metallic nano-materials attract much interests not only because of their potential application to novel electronic devices but fundamental low-dimensional physics point of view. One of the ways to fabricate nano-materials is to deposit small amount of metal atoms on crystalline semiconductor surfaces. In the present study, we have investigated atomic and electronic structures of gold adsorbed Ge(001) and Ge(111) surfaces which exhibit one- and two-dimensional atomic structure, respectively, by scanning tunneling microscopy (STM), angle-resolved photoelectron spectroscopy (ARPES) and density functional calculations.

The Au-adsorbed Ge(001) surface has periodic arrangement of one-dimensional (1D) chain structure and a metallic surface state. This metallic state has been reported to be strictly 1D showing Tomonaga-Luttinger liquid (TLL) behavior[1]. In the present study, its band shape was precisely investigated using a single-domain surface prepared on a vicinal substrate. Our ARPES results clearly revealed that the band has anisotropic two-dimensional (2D) shape in contrast to the previous report. The band dispersion is steeper in the direction perpendicular to the chain contrary to the intuitive expectation from 1D structure[2]. Our STM study revealed that the top of the 1D chain shows 8 times periodicity on average along the chain with a lot of defects[3]. This rather high density of defects may cause the reduction of density of states at the Fermi level which was previously interpreted as a TLL behavior.

The Au-adsorbed Ge(111) surface exhibits √3×√3 periodicity. Two metallic surface states, S₁ and S₂, were observed around Γ, which is consistent with the calculated band structure of the CHCT model. 2D electronic system is confirmed by a rounded hexagonal Fermi surface of S₁ band[4] which has contributions from surface Au and Ge atoms. S₂ is originated only from the Ge atoms. These surface bands split into spin-polarized bands owing to the strong spin-orbit interaction[5]. The modification of the electron filling of the S₁ band by additional Au atoms will be also discussed[6].

The author thanks Y. Motomura, R. Niikura and Prof. F. Komori in Institute for Solid State Physics, University of Tokyo for their close collaboration, and Y. Oda and Prof. A. Ishii in Tottori University for their collaboration in theoretical part of this work.

[1] C. Blumenstein et al., Nature Physics 7 (2011) 776.

[2] K. Nakatsuji et al., PRB 84 (2011) 115411.

[3] R. Niikura et al., PRB 83 (2011) 035311.

[4] K. Nakatsuji et al., PRB 80 (2009) 081406®.

[5] K. Nakatsuji et al., PRB 84 (2011) 035436.

[6] K. Nakatsuji et al., JPCM 25 (2013) 045007.