Optical read-out of Coulomb staircases in a moiré superlattice via trapped interlayer trions

Abstract

Moiré patterns with a superlattice potential can be formed by vertically stacking two layered materials with a relative twist or lattice constant mismatch. In transition metal dichalcogenide-based systems, the moiré potential landscape can trap interlayer excitons (IXs) at specific atomic registries. Here, we report that spatially isolated trapped IXs in a molybdenum diselenide/tungsten diselenide heterobilayer device provide a sensitive optical probe of carrier filling in their immediate environment. By mapping the spatial positions of individual trapped IXs, we are able to spectrally track the emitters as the moiré lattice is filled with excess carriers. Upon initial doping of the heterobilayer, neutral trapped IXs form charged IXs (IX trions) uniformly with a binding energy of ~7 meV. Upon further doping, the empty superlattice sites sequentially fill, creating a Coulomb staircase: stepwise changes in the IX trion emission energy due to Coulomb interactions with carriers at nearest-neighbour moiré sites. This non-invasive, highly local technique can complement transport and non-local optical sensing techniques to characterize Coulomb interaction energies, visualize charge correlated states, or probe local disorder in a moiré superlattice.

Localized interlayer excitons in MoSe2–WSe2 heterostructures without a moiré potential

“…The relatively small intrinsic doping range (−0.1 to 0.1 × 10 12 cm −2 ) is consistent with a high quality device. We note that in both regions, the IX energy increases with doping, which is consistent with previous reports 13 , 16 . We also note that the DC region shows more prominent fine structure in its doping dependence which was previously attributed to a Coulomb staircase effect 13 (see Supplementary Fig.…”

Exciton-polarons in the presence of strongly correlated electronic states in a MoSe$_2$/WSe$_2$ moiré superlattice

“…Further investigations could exploit the small lattice mismatch between MoSe 2 /WSe 2 , which enables a highly tunable moiré period, to simulate condensed matter phase diagrams over a large range of U/t ratios. Our observation of the formation of flat electronic bands compliments recent reports of moiré trapped interlayer excitons in MoSe 2 /WSe 2 hetero-bilayers [32][33][34][35][36][37][38] and highlights the exciting prospects to investigate Fermi-Hubbard and Bose-Hubbard physics in this system. knowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan (Grant Number JPMXP0112101001) and JSPS KAKENHI (Grant Numbers 19H05790, 20H00354 and 21H05233).…”

“…1c) [44,45]. The interlayer excitons can be confined by the moiré potential at specific atomic registries giving rise to quantum-dot-like light emission [32][33][34], as demonstrated for both neutral and charged interlayer excitons in our device [34,36,37].…”

“…In addition, the moiré potential in WSe 2 /MoSe 2 heterobilayers has led to the observation of trapping of interlayer excitons at specific atomic registries in the moiré lattice [31][32][33][34][35][36][37][38]. To date, hetero-bilayer WSe 2 /MoSe 2 remains the only moiré system to conclusively exhibit exciton trapping.…”

The Magnetic Genome of Two-Dimensional van der Waals Materials

“…For example, interlayer excitons localized in the moiré potential created by a TMD heterobilayer feature spin- and valley-dependent optical transitions with line widths below 100 μeV and g -factors as large as | g |∼ 16. 207 , 241 − 245 These localized interlayer excitons and trions might prove useful to keep exploring the emerging field of magnetic phenomena in 2D vdW crystals.…”