Magneto-spectroscopy of Highly-Aligned Carbon Nanotubes: Identifying the Role of Threading Magnetic Flux

TL;DR

This study uses magneto-spectroscopy to analyze excitons in highly-aligned single-walled carbon nanotubes, revealing the magnetic flux's role and providing a theoretical model that matches experimental data.

Contribution

It introduces a theoretical model of one-dimensional magneto-excitons that explains experimental observations in aligned SWCNTs under high magnetic fields.

Findings

Photoluminescence energy and intensity depend only on the magnetic field component parallel to nanotube axes.

Theoretical model reproduces experimental magneto-exciton behavior.

Splitting between bright and dark exciton bands is approximately 4.8 meV for (6,5) SWCNTs.

Abstract

We have investigated excitons in highly-aligned single-walled carbon nanotubes (SWCNTs) through optical spectroscopy at low temperature (1.5 K) and high magnetic fields ($\textbf{\textit{B}}$) up to 55 T. SWCNT/polyacrylic acid films were stretched, giving SWCNTs that are highly aligned along the direction of stretch ($\hat{n}$). Utilizing two well-defined measurement geometries, $\hat{n}\parallel\textbf{\textit{B}}$ and $\hat{n}\perp\textbf{\textit{B}}$, we provide unambiguous evidence that the photoluminescence energy and intensity are only sensitive to the $\textbf{\textit{B}}$-component parallel to the tube axis. A theoretical model of one-dimensional magneto-excitons, based on exchange-split `bright' and `dark' exciton bands with Aharonov-Bohm-phase-dependent energies, masses, and oscillator strengths, successfully reproduces our observations and allows determination of the splitting between the two bands as $\sim4.8$ meV for (6,5) SWCNTs.