Quantum structures made with carbon nanotubes

LTL Quantum Physics Seminar (Nanotalo). Speaker: Dr. Akira Hida (RIKEN, Japan).

I present two types of artificial nano-structures made with single-walled carbon nanotubes (SWNTs): SWNT rings and hetrostructures of SWNTs and collagen model peptides. In the first half of the talk, I begin with how to make SWNT rings and then show the Aharonov-Bohm oscillations observed in them. Since the diameters of SWNTs are small and also uniform in the longitudinal direction, the Aharonov-Bohm ring with ideally narrow linewidth might be obtained by forming SWNTs into the ring shape. In the direct observations of the SWNT rings using a scanning tunneling microscope, standing wave patterns due to the interference of injected electrons appear along the circumference of the ring. At 5 K, the Aharonov-Bohm oscillations with the amplitude up to ~90 % of the conductance are observed. The amplitude decreases with increasing temperature and disappears almost entirely above 10 K. The temperature dependence of the amplitude shows that the main decoherence factor is thermal broadening of the electron energy in the low temperature region and the phase breaking scattering at higher temperatures.

In the latter half, I show some results on the hetrostructures of SWNTs and collagen model peptides that are the molecules synthesized after the model of natural collagen. Scanning tunneling spectroscopy reveals that a confinement potential is formed when collagen model peptides are attached to both ends of an individual SWNT via the formation of carboxylic anhydrides. On the other hand, the confinement potential is markedly changed by yielding the peptide bonds between the SWNT and the collagen model peptides. Photoluminescence spectroscopy measurements show that a type-II quantum dot is produced in the heterostructure.