(Invited) The Moiré Structure of Double Walled Carbon Nanotubes Affects Their Electronic and Vibrational States

Abstract

Double walled carbon nanotubes (DWCNT) are formed from two concentric single walled carbon nanotubes. They are a one-dimensional moiré system where the coupling strength between the two walls varies greatly depending on the atomic structure of the two tubes. In this talk we discuss the effect of moiré coupling on the electronic and vibrational states of DWCNTs. We focus on the regime of strong moiré coupling and the combination of semiconducting inner and semiconducting outer tube. For such DWCNTs moiré coupling leads to a red-shift of most optical transition energies. The coupling also affects the frequency of the radial breathing mode (RBM), which is an unexpected finding in connection with moiré interaction. We predict a linear correlation between the change in RBM frequency and in optical transition energy. To verify our predictions we will present resonant Raman experiments on DWCNTs sorted by metallic character. We show that the splitting of the RBM frequencies in DWCNT samples is a clear manifestation of the moiré coupling and construct a Kataura plot for the assignment of double walled tubes. Using resonance Raman profiles of the RBM we confirm the correlation between electronic and vibrational shifts. We also discuss the effect of dielectric screening on the Raman intensities. Our work shows how moiré coupling can strongly affect the vibrational in addition to the electronic and optical states of a one-dimensional system.