Probing Luttinger Liquid Plasmons in Single Walled Carbon Nanotubes

Single walled carbon nanotubes (SWNTs) are one-dimensional (1D) rolled-up hollow cylinders composed of graphene sheets. Since their discovery about three decades ago, they have been one of the most fascinating and unique nanoscale structures. There have been tremendous and still ongoing research on SWNTs for both fundamental science as well as technological devices. SWNTs have been a good platform to study electron-electron interaction in solid state systems, including Coulomb blockage effect and Luttinger liquid formulism. SWNTs exhibit unique electrical, mechanical and thermal properties, making them potentially useful in a variety of applications including nano-electronics, optics, energy storage, and nanomedicine. Notably, carbon nanotube field-effect transistor-based digital circuits may be a viable route for next-generation beyond-silicon electronic systems for post-Moore’s Law era. Recent major advance includes a 16-bit computer built entirely from carbon nanotube transistors. Despite the intense established research, SWNTs have never ceased to surprise researchers with their emerging properties and potential applications. During the past decade, advances in the synthesis and processing have enabled the controlled growth of high quality ultralong SWNTs on different substrates even with desirable chirality. On the other hand, developments in powerful surface science characterization tools provide a viable route to probe the electronic and optical properties of individual SWNTs. We take advantage of these advances mainly in two ways. First, we grow ultraclean and very long SWNTs on hexagonal boron nitride (h-BN) flakes and fabricate them into field-effect transistor (FET) devices to tune their carrier density. Second, we optimize the performance of recently developed infrared scanning near-field microscopy (IR-SNOM) to achieve measurements of plasmonic excitations of individual SWNTs even at low electron densities. In the first chapter of the dissertation, I will introduce the fundamental properties of SWNTs. I will also discuss the Luttinger liquid formulism in 1D systems and the emerging nonlinear Luttinger liquid theory accounting for the effects of nonlinear band dispersion on the electron excitations. IR-SNOM, the main experiment tool we employ to probe the Luttinger liquid plasmons, will also be introduced. In the following chapters, I will discuss our findings and understandings achieved by infrared nanoimaging of SWNT FET devices supplemented with electronic transport. We experimentally demonstrate the logarithm diameter scaling and carrier density independence of Luttinger liquid plasmons in metallic SWNTs. The unusual behaviors are signatures of the Luttinger liquid and stand in sharp contrast with conventional plasmons in metallic nanoshells. We further correlate infrared nano-imaging measurements and electrical tunneling at a cross junction between two metallic SWNTs, providing a parameter free test of the Luttinger liquid theory in SWNTs. While metallic SWNTs with linear band dispersion are perfect realizations of the linear Luttinger liquid, semiconducting SWNTs featuring hyperbolic band dispersion deviates from the paradigm. We demonstrate that electric-field tunable plasmonic excitations in semiconducting SWNTs behave consistently with the nonlinear Luttinger liquid theory, providing a platform to study non-conventional one-dimensional electron dynamics and realize integrated nanophotonic devices. We further fabricate individual SWNT nanocavities of controllable length by scanning probe nanolithography. We resolve the plasmon resonance of individual nanotube cavities by spectrally resolved infrared nanoimaging. These findings and understandings reveal the unusual 1D electron dynamics in metallic and semiconducting SWNTs and lay the foundation for carbon nanotube plasmonics