Charge Density Wave Activated Excitons in TiSe$_2$-MoSe$_2$ Heterostructures

TL;DR

This study discovers a novel excitonic photoluminescence peak at the TiSe$_2$-MoSe$_2$ interface, influenced by charge density waves, opening new avenues for exciton engineering in layered heterostructures.

Contribution

It reports the observation of a new excitonic feature linked to charge density waves in TiSe$_2$-MoSe$_2$ heterostructures, highlighting unexplored physics at dissimilar material interfaces.

Findings

Unique PL peak at the interface

Peak disappears at charge density wave transition

Potential for exciton engineering via charge density waves

Abstract

Layered materials enable the assembly of a new class of heterostructures where lattice-matching is no longer a requirement. Interfaces in these heterostructures therefore become a fertile ground for unexplored physics as dissimilar phenomena can be coupled via proximity effects. In this article we identify an unexpected photoluminescence (PL) peak when MoSe$_2$ interacts with TiSe$_2$. A series of temperature-dependent and spatially-resolved PL measurements reveal this peak is unique to the TiSe$_2$-MoSe$_2$ interface, higher in energy compared to the neutral exciton, and exhibits exciton-like characteristics. The feature disappears at the TiSe$_2$ charge density wave transition, suggesting that the density wave plays an important role in the formation of this new exciton. We present several plausible scenarios regarding the origin of this peak that individually capture some aspects of our observations, but cannot fully explain this feature. These results therefore represent a fresh challenge for the theoretical community and provide a fascinating way to engineer excitons through interactions with charge density waves.