Chiral trions in enantiopure single-wall carbon nanotubes

A trion is a charged exciton, which can be observed in many low-dimensional semiconductors. Circular dichroism (CD) of trions was demonstrated based on optical transitions following their spin selection rules, such as spin states of semiconductor quantum dots and valley spin polarization in monolayer two-dimensional materials. However, the configurational CD of trions, which is uniquely caused by chiral structures, has never been observed. In this study, the CD of trions in enantiopure single-wall carbon nanotubes (SWCNTs) is demonstrated. Depending on the right- or left-handedness of the SWCNTs, the sign of the trion CD changes and is the same as that of the original exciton CD. Consequently, chiral trions exist in chiral SWCNTs. Here, the authors unveil the circular dichroism of trions in enantiopure single-walled carbon nanotubes, indicating chiroptical characteristics that reflect those of the parent excitons and remain robust in a Coulomb-bound three-body system.