Bandgap renormalization in single-wall carbon nanotubes

Abstract

Single-wall carbon nanotubes (SWNTs) have been extensively explored as an ultrafast nonlinear optical material. However, due to the numerous electronic and morphological arrangements, a simple and self-contained physical model that can unambiguously account for the rich photocarrier dynamics in SWNTs is still absent. Here, by performing broadband degenerate and non-degenerate pump-probe experiments on SWNTs of different chiralities and morphologies, we reveal strong evidences for the existence of bandgap renormalization in SWNTs. In particularly, it is found that the broadband transient response of SWNTs can be well explained by the combined effects of Pauli blocking and bandgap renormalization, and the distinct dynamics is further influenced by the different sensitivity of degenerate and non-degenerate measurements to these two concurrent effects. Furthermore, we attribute optical-phonon bath thermalization as an underlying mechanism for the observed bandgap renormalization. Our findings provide new guidelines for interpreting the broadband optical response of carbon nanotubes.

Broadband photocarrier dynamics and nonlinear absorption of PLD-grown WTe2 semimetal films

“…The presence of broadband and unifying feature means that linewidth broadening effects, which typically involve the change of signal polarity at a specific transition photon energy, do not play a major role. [17][18][19] We further confirmed the experimental observation by carrying out pump-probe spectroscopy using an 80 MHz Ti:Sapphire OPO system, and the results with a probe wavelength down to 1.2 lm show qualitatively very similar response (Fig. S7).…”

Layer-Dependent Ultrafast Carrier and Coherent Phonon Dynamics in Black Phosphorus

“…29 BGR is primarily due to the change of electronic occupation that alters the dielectric screening and affects all electronic states simultaneously and thus could be observed in all excitonic transitions. 22,23 The detailed balance between band gap shrinkage and exciton binding energy may depend on the energy level and partly results in the reduced PB resonances in higher excitonic transitions. Although the pump photon energy is slightly lower than the probe energy in our study, this indeed reduces the contribution of Pauli blocking.…”

Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures

“…Similar blueshifts were seen for the B exciton and the interband oscillator at 2.25 eV under IR excitation (Figure S7, Supporting Information), whereas direct excitation of the MoS 2 NTs at 3.0 eV produced a redshift in the A exciton energy as a result of bandgap renormalization. [ 27 ] Within the coherent regime (during the IR pulse), the blueshift may be understood as an optical Stark shift of the exciton energies in the MoS 2 . Alternatively, with a finite population in state E |10〉 there is an excited state absorption pathway (dashed line in Figure 1f) at an energy E |11〉 − E |10〉 = E |01〉 − E |00〉 − Δ, that is, an energy Δ below the excitonic resonances of the MoS 2 NTs.…”