1, National University of Singapore, Singapore, , Singapore
3, National University of Singapore, Singapore, , Singapore
4, Rice University, Houston, Texas, United States
Recently, there have been several efforts in creating Van der Waals heterostructures of 2D materials to investigate many body interactions of their excitons and trions, which often give rise to unusual functionalities at the interface. However, there are certain exclusive functionalities like presence of soft phonon modes, which is seldom observed in 2D materials due to stringent symmetry requirements. SrTiO3 (STO) is a transition metal oxide well known for the presence of a soft phonon mode below 105 K. This phonon mode is also polar in nature, thus enabling columbic interactions with quasiparticles around it. In this work, we have been able to create a heterostructure of MoS2 and SrTiO3 (STO) by direct CVD growth, and we observe from photoluminescence measurements that as the soft phonons evolve in STO, the trion peak exhibits a significant red shift as compared to emission from MoS2 grown on various other substrates without soft phonons. From femtosecond pump probe spectroscopy we calculate the lifetimes of the trion in MoS2 (10 ps), which is in the same time scales as the frequency of polar soft phonon modes in STO. This enables the polar phonons and the trion to selectively couple with the charged trions in MoS2 to form a quasi-stationary bound state, which we call the ‘Polaronic Trion’. We demonstrate tunability of the light emission from the Polaronic Trion by almost 90 meV by simply varying electric field (which suppresses the phonons), temperature or even crystal orientation. Such an unprecedented selective tunability of the trion could probably guide actual applications for the much investigated quasiparticles in 2D materials.