Magnetic Brightening of Carbon Nanotube Photoluminescence through Symmetry Breaking

TL;DR

Applying a magnetic field to single-walled carbon nanotubes breaks their symmetry, significantly enhancing their photoluminescence by up to six times through exciton state manipulation, as explained by a new theoretical model.

Contribution

This work demonstrates the first experimental observation of dark excitons below bright excitons in nanotubes and introduces a theoretical model linking magnetic symmetry breaking to photoluminescence enhancement.

Findings

Photoluminescence quantum yield increases by up to six times at low temperatures.

Dark excitons are observed 5-10 meV below bright excitons.

Magnetic field-induced symmetry breaking explains the luminescence enhancement.

Abstract

Often a modification of microscopic symmetry in a system can result in a dramatic change in its macroscopic properties. Here we report that symmetry breaking by a tube-threading magnetic field can drastically increase the photoluminescence quantum yield of semiconducting single-walled carbon nanotubes, by as much as a factor of six, at low temperatures. To explain this striking connection between seemingly unrelated properties, we have developed a comprehensive theoretical model based on magnetic-field-dependent one-dimensional exciton band structure and the interplay of strong Coulomb interactions and the Aharonov-Bohm effect. This conclusively explains our data as the first experimental observation of dark excitons 5-10 meV below the bright excitons in single-walled carbon nanotubes. We predict that this quantum yield increase can be made much larger in disorder-free samples.