Biexciton Stability in Carbon Nanotubes

Abstract

We have applied the quantum Monte Carlo method and tight-binding modeling to calculate the binding energy of biexcitons in semiconductor carbon nanotubes for a wide range of diameters and chiralities. For typical nanotube diameters we find that biexciton binding energies are much larger than previously predicted from variational methods, which easily brings the biexciton binding energy above the room temperature threshold.

Theory and application of explicitly correlated Gaussians

“…Results from the ''exact'' diagonalization, DIAG (Hawrylak and Pfannkuche, 1993) and three DMC calculations DMC1 (Bolton, 1996), DMC2 (Pederiva, Umrigar, and Lipparini, 2000), and DMC3 (Harju et al, 1999) are determined by quantum mechanical few-body systems. Carbon nanotubes, for example, offer a novel challenge for few-body approaches where the electrons and holes move on the surface of a cylinder (Pedersen et al, 2005;Kammerlander et al, 2007;Roy and Maksym, 2012). This is a ''fractional dimensional'' few-body system where the 2D problem is embedded into 3D space and one has to use either an appropriate confining potential or an appropriately constrained ECG basis.…”

Multi-excitonic effects on optical spectra of semiconducting carbon nanotubes

“…On the other hand, it slowly increases and saturates as ∆ decreases, and we can extrapolate E XX as 0.031. This value is slightly larger than that obtained by the variational method [4], and about 30 percent smaller than that obtained by DMC method [5]. These results shows that the short-wavelength components are relatively important in the biexciton wavefunction, and give a considerable correction to the value of E XX .…”

“…It is about 2 percent smaller than that obtained with the diffusion Monte Carlo (DMC) method [5], in which not only the ground but excited subbands are considered. We also find that the nonparabolicity effects reduce the exciton binding energy only by 5 percent.…”

“…In the following, we measure the length in units of the radius R, and the energy in units of γ/R. Then, this model is characterized by only one dimensionless coupling constant v c = e 2 /κγ, which we fix to 0.6 in our calculation [5]. We apply the finite difference method to our model: the one dimensional system is discretized on a grid with interval ∆ [8,9] under the periodic boundary condition, where the distance between the ith and jth grid points is defined as r ij = ∆ Min (|i − j|, M − |i − j|) with the number of grid points, M .…”

“…Because of their one dimensionality, it is found both theoretically [2] and experimentally [3] that the excitons on the semiconducting carbon nanotubes (s-CNTs) have huge binding energies. Further, theoretical studies also predict stable biexcitons with large binding energies [4,5]. However, they have never been observed in the photoluminescence (PL) measurements [6].…”