Observation of Polaronic Trions in MoS₂/SrTiO₃ Heterostructures

One of the primary challenges in condensed matter physics has been to understand the dynamics of many body interactions of quasiparticles. Recently, the three body charged quasiparticle, trion, has attracted a lot of attention, due to its large binding energies in 2D transition metal dichalcogenide (TMD) semiconductors, and their have been several efforts to tune its properties. The tunability of trion using phonon interactions has not yet been achieved due to the lack of low frequency phonons in 2D systems. In this work, for the first time, we demonstrate trion-phonon interactions across the interface of a MoS₂/SrTiO₃ heterostructure. From PL emission experiments, we observe that the low frequency (soft) phonon mode in SrTiO₃, due to its polar nature, selectively couples 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 varying electric field, temperature or even crystal orientation. Such an unprecedented selective tunability of the trion would probably guide practical applications for the much investigated quasiparticles in 2D materials.