A new quasiparticle in carbon nanotubes

Abstract

We report the first observation of trions (charged excitons), three-particle bound states consisting of one electron and two holes, in hole-doped carbon nanotubes at room temperature. When p-type dopants are added to carbon nanotube solutions, the photoluminescence and absorption peaks of the trions appear far below the E 11 bright exciton peak, regardless of the dopant species. The unexpectedly large energy separation between the bright excitons and the trions is attributed to the strong electron-hole exchange interaction in carbon nanotubes. DOI: 10.1103/PhysRevLett.106.037404 PACS numbers: 78.67.Ch, 71.35.Pq, 78.55.Àm Because of their unique mechanical, optical, and electronic properties, single-walled carbon nanotubes have been of great interest in broad research fields over the past decade [1]. One of the most prominent characteristics of carbon nanotubes is the strong correlation between carriers due to the quantum confinement that occurs in one-dimensional (1D) structures of about 1 nm diameter. Electron-electron repulsive and electron-hole attractive interactions play important roles in the electronic and optical properties [2], resulting in the formation of excitons with huge binding energies in semiconducting carbon nanotubes [3], and even in metallic carbon nanotubes [4].Despite the importance of carrier correlations in carbon nanotubes, many-particle bound states, such as excitonexciton or exciton-electron(hole) complexes, are not yet fully understood. Excitonic molecules (biexcitons) have not been observed in carbon nanotubes even under intense excitation conditions at low temperatures [5]. In addition, there has been no report of observation of exciton-carrier bound states (charged excitons or trions) in carbon nanotubes, although many optical measurements have been performed with carrier doping [6][7][8][9][10][11]. Meanwhile, the carrier-doping effect on nanotube field-effect transistors has been investigated for controlling and switching the optical properties of nanotube devices [12,13]. Additionally, a recent ab initio calculation has shown that the band gap can be tuned by dynamical screening of acoustic plasmons in hole-doped carbon nanotubes [14]. Thus, experimental studies of the optical properties of carrier-doped carbon nanotubes are quite important not only for understanding many-particle correlations in 1D structures, but also for future nanoscale device applications.In this Letter, we report the existence of a new excited state below the lowest (E 11 ) singlet exciton state in holedoped single-walled carbon nanotubes. In both photoluminescence (PL) and absorption spectroscopy, a new peak appears with hole doping at room temperature, regardless of the dopant species. This PL peak is completely different from the luminescence of optically forbidden excitons reported recently [15][16][17][18][19]. Moreover, the energy separation between the new state and the E 11 bright exciton state shows clear ''family patterns,'' similar to the exciton binding energy in carbon nanotubes. These res...

Dispersing Perylene Diimide/SWCNT Hybrids: Structural Insights at the Molecular Level and Fabricating Advanced Materials

“…Strong changes in charge densities from SWCNTs to PDIs have been seen in the past to lead to similar spectroscopic signatures . Characteristic charge transfer-induced shifts of the photoluminescence in n-doped SWCNTs are ∼0.04 eV. , In addition, electrochemical and chemical doping of SWCNTs have evoked large shifts in the emission peaks, which have been attributed to the presence of trions. − The stability of trions in SWCNTs at room temperature has been analyzed on the basis of a tight-binding model …”

“…The effect was more pronounced in the case of PP3a, indicating that the enrichment of (7,6)-SWCNTs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 10 in the presence of PDIs is apparently more significant in the case of PP3a. [47][48][49][50][51][52][53] The stability of trions in SWCNTs at room temperature has been analyzed on the basis of a tight-binding model. …”