Anisotropic band structure of TiS3 nanoribbon revealed by polarized photocurrent spectroscopy

A re-discovered member of the layered material family, Titanium Trisulfide (TiS3), has attracted intense research interest recently for the possibility of realizing an exciton insulator in the monolayer limit. However, due to their quasi-one-dimensional nature, thin TiS3 flakes are typically in the form of nanoribbons that are challenging to characterize by optical absorption spectra, due to their small cross section. Here, we employ a sensitive photocurrent spectroscopy technique to probe the absorption of a thin TiS3 nanoribbon in a field-effect transistor configuration. We have found a significant modification of the band structure of the thin TiS3 nanoribbon, compared to its bulk counterpart. In addition, the polarization-dependent photocurrent spectra of thin TiS3 nanoribbons exhibit greatly enhanced anisotropy compared to that of a thick TiS3 device. The atomically thin TiS3 flake, thus, not only provides an exciting platform for investigating many-body physics but also enables anisotropic quantum optoelectronics.