High-Field Magneto-Photoluminescence Spectroscopy of Highly-Aligned Carbon Nanotubes

We have investigated excitons in semiconducting single-walled carbon nanotubes (SWNTs) through low-temperature magneto-photoluminescence (PL) of highly-aligned SWNT films in magnetic fields ($\textbf{\textit{B}}$) up to 55~T. The magnetic field was generated using the 60~T long pulse magnet powered by a 1.4 GVA motor-generator at the National High Magnetic Field Lab in Los Alamos, NM. Polyacrylic acid films containing DNA suspended CoMoCAT SWNTs were stretch-aligned, and the alignment factor was analyzed by polarized Raman spectroscopy$^1$. Utilizing two well-defined measurement geometries, SWNTs~$\parallel$~$\textbf{\textit{B}}$ and SWNTs~$\perp$~$\textbf{\textit{B}}$, we provide unambiguous evidence that the PL from excitons in SWNTs is sensitive only to the $\textbf{\textit{B}}$-component parallel to the tube axis. We developed a theoretical model of one-dimensional magneto-excitons, based on recently-proposed exchange-split bright and dark exciton bands with Aharonov-Bohm-phase-dependent energies, masses, and oscillator strengths, which successfully reproduces our observations$^2$. \newline 1. Fagan \textit{et al.} Phys. Rev. Lett. \textbf{98}, 147402 (2007) \newline 2. Shaver \textit{et al.} Nano Lett. \textbf{7}, 1851 (2007)