Near-infrared magneto-optical study of excitonic states in single-walled carbon nanotubes under ultra-high magnetic fields

Singlet excitonic states at the first subband-edge in single-walled carbon nanotubes(SWCNTs) have been studied through near-infrared magneto-absorption spectroscopy undermagnetic fields to 105.9 T. Well-resolved absorption spectra of stretch-alignedSWCNT(CoMoCAT)-gelatin films were obtained above 100 T. By the application of magneticfields in parallel to the alignment of SWCNTs, peak shift toward the lower energy wasobserved for (8, 4) and (7, 6) tubes and the opposite behavior was observed for (7, 5) and (6, 5)tubes. Above 28.8 T, new peaks emerged at the higher energy side of the peak for the (8, 4)and (7, 6) tubes, and at the lower energy side of the peaks for the (7, 5) and (6, 5) tubes. Themagnetic splitting between the existing peak and the new peak was symmetric for every tube,which is in line with the energy splitting due to the Aharonov-Bohm effect. Judging from theenergetic positions where the new peaks emerged, the singlet dark excitonic state locates at thelower energy than the singlet bright one in the (7, 5) and (6, 5) tubes while it is suggestedstrongly that the bright one locates at the lower energy in the (8, 4) and (7, 6) tubes