Ultrafast terahertz probes of interacting dark excitons in chirality-specific semiconducting single-walled carbon nanotubes

TL;DR

This paper demonstrates ultrafast terahertz spectroscopy as a powerful tool to probe dark excitons in semiconducting carbon nanotubes, revealing their dynamics, interactions, and phase-space filling effects.

Contribution

It introduces an analytical model for interpreting terahertz responses, enabling quantitative analysis of dark exciton properties and their behavior under various excitation conditions.

Findings

Dark excitons can be directly probed via terahertz transitions.

Non-equilibrium dark excitonic states rapidly form and evolve.

Distinct phase-space filling behavior differs from higher-dimensional systems.

Abstract

Ultrafast terahertz spectroscopy accesses the {\em dark} excitonic ground state in resonantly-excited (6,5) SWNTs via internal, direct dipole-allowed transitions between lowest lying dark-bright pair state $\sim$6 meV. An analytical model reproduces the response which enables quantitative analysis of transient densities of dark excitons and {\em e-h} plasma, oscillator strength, transition energy renormalization and dynamics. %excitation-induced renormalization. Non-equilibrium, yet stable, quasi-1D quantum states with dark excitonic correlations rapidly emerge even with increasing off-resonance photoexcitation and experience a unique crossover to complex phase-space filling of %a complex distribution between both dark and bright pair states, different from dense 2D/3D excitons influenced by the thermalization, cooling and ionization to free carriers.