ARPES Investigation of Dispersive Excitons in Low-Dimensional Topological Materials

Traditional electronic devices that transfer information are based on electrical charges, which can be easily disturbed by environmental factors. In contrast, excitons, i.e., electron-hole pairs, are mobile and neutral in charge and are thus potentially superiorinformation transmitters. Excitons in semiconductors are common and widely studied through optical methods. However, in metals, the screening effect by free electrons usually prevents the formation of excitons or allows them to appear only transiently. Asoptical methods cannot provide momentum information, angle-resolved photoemission spectroscopy studies of excitons have gained interest in recent years since they can provide direct insight into momentum space. Recently, we discovered with angleresolvedphotoemission spectroscopy that robust dispersive (highly mobile) excitons can exist in quasi-one-dimensional metallic TaSe3 with nontrivial band topology, in which the internal crystal structures resemble parallel straight stripes. Another importantrecent development is the prediction and discovery of topological materials, which have unique electronic structures. Detecting and manipulating topological materials is important, as their physical properties have potential in future practical electronicapplications. Thus, excitons in topological materials have wide-ranging applications, such as next-generation electronic devices for digital information transfer and photoelectric information conversion.In this proposed project, we aim to detect, analyze, and manipulate dispersive excitons in low-dimensional topological materials with angle-resolved photoemission spectroscopy, as the low-dimensionality is favorable for directional transmission, and can enhance therobustness of excitons. Traditional excitons in semiconductors usually have small group velocities, limiting their mobility during transmission. However, dispersive excitons with finite velocity will increase the exciton mobility and information-transferring efficiency.We will first focus on manipulating the dispersive excitonic states in TaSe3. We will then search for new robust dispersive excitonic states in low-dimensional topological metals such as in the RNiC2 (where R is a rare earth element) family to confirm whether thepresence of the dispersive excitons is universal. By the completion of this project, we expect to have detected and manipulated dispersive excitons in TaSe3 and RNiC2 and to have a clearer understanding of the properties of the mobile excitons. In addition toproviding an update for the condensed matter physics research community, our findings will have future benefits in electronic device applications for high-technology startup firms, which may create more employment opportunities for society.