Tokyo, Japan – Scientists from Tokyo Metropolitan University have discovered that charged states made of two electrons and a positively charged hole (or vice versa) on atomically thin rolls of carbon atoms have a structure-derived “handedness” in how they interact with light. While electron-hole pairs, or “excitons,” were known to keep the chirality of the underlying nanotube, the team showed that adding a charge to create “trions” does not change this property. Their work highlights new ways in which carbon nanotubes might be used in next-gen optoelectronic devices.
Chirality is a fascinating feature of the material world. Whether it be a circular staircase, a wrung towel, double-stranded DNA, or pharmaceutical molecules, an object can often have a “handedness” which means that its mirror image will never be matched with itself. This extends to the nature of light. Circularly polarized light has an electromagnetic field that rotates either left or right along its direction of travel. Light like this can interact differently with materials which have their own chirality in their structure. Known as circular dichroism, researchers believe this is a key property for manipulating light and electric current in nanotechnology.
Single-walled carbon nanotubes (SWCNTs), ultra-thin rolled up cylinders of carbon atoms, are one of the frontrunners for getting chirality into future devices. Like a twisted rolled-up newspaper, the tube surface can have a handedness, depending on how the atoms are arranged. These left and right-handed carbon nanotubes can house excitons, pairs of negatively charged electrons and positively charged holes, which themselves show a circular dichroism depending on the chirality of the underlying nanotube. Excitons on carbon nanotubes are particularly interesting for applications, since they are stable at room temperature. However, they are the tip of the iceberg for the whole range of states which can be created. For example, the pairs can have an added electron or hole, leading to a charged “trion.” While potentially useful, a key issue remained in whether adding an extra charged particle would affect its chiral properties, particularly whether the “structure-derived” chirality of the original exciton would be preserved.
Now, a team led by Professor Kazuhiro Yanagi from Tokyo Metropolitan University has addressed this problem using specially separated samples of left and right-handed SWCNTs. By generating trions using electrochemistry, they were able to quantify their circular dichroism with unprecedented precision. Their measurements showed that the chirality of the trions matched the excitons from which they were made, accurately reflecting the chirality of the underlying SWCNT. The degree of chirality was also found to be roughly the same as the original excitons.
Since trions can be easily created by injecting electrons or holes into SWCNTs, this paves the wave for electrically controlling the degree to which they interact with circularly polarized light. This may lead to exciting new technologies, such as light amplification, detection and modulation.
This work was supported by the MIYAKO-MIRAI Project of Tokyo Metropolitan University, JSPS KAKENHI Grant Numbers JP21H05017, JP23H00259, JP24H01200, and JPJSBP120252302, the JST CREST Program through Grant Number JPMJCR2544, the US-JAPAN PIRE collaboration, Grant Number JPJSJRP20221202, a Tokyo Metropolitan Government Advanced Research Grant Number (H31-1), the ASPIRE project, Grant Number JPMJAP2310, the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via SFB 1225/3 (Isoquant), and the United States National Science Foundation through Grant Number 2230727.
Nature Communications
Chiral trions in enantiopure single-wall carbon nanotubes
30-Sep-2026