September 29, 2021 feature
Researchers observe moiré trions in H-stacked transition metal dichalcogenide bilayers
In physics, the moiré pattern is a specific geometrical design in which sets of straight or curved lines are superposed on top of each other. Recent studies have found that bilayers of transition metal dichalcogenide materials arranged in moiré patterns could be particularly promising for studying electronic phenomena and excitons (i.e., concentrations of energy in crystals formed by an excited electron and an associated hole).
Transition metal dichalcogenide moiré bilayers have advantageous characteristics for studying both electronic and excitonic physical phenomena, including strong Coulomb interactions. Past research studies have successfully used these systems to make several interesting discoveries, such as exotic charge orders at both integer and fractional fillings.
Researchers at University of Washington and other institutes worldwide have recently carried out a study specifically examining a Transition metal dichalcogenide moiré system comprised of molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers, Their paper, published in Nature Nanotechnology, reports the observation of moiré-arranged trions (i.e., localized excitations consisting of three charged particles) in H-stacked MoSe2/WSe2 heterobilayers.
"Periodic moiré potential naturally occurs in transitional metal dichalcogenides moiré superlattices. Several years ago, we envisioned that the periodic potential can function as arrays of quantum dots," Wang Yao, one of the researchers who carried out the study, told TechXplore. "Based on this idea, our team demonstrated charge neutral moiré excitons in twisted MoSe2/WSe2 heterobilayers in 2019."
The work builds on the group's previous studies focusing on transitional metal dichalcogenides moiré superlattices. While in their past research, the team was able to observe charge-neutral moiré excitons in twisted MoSe2/WSe2 heterobilayers, in their new study, they tried to add the electrostatic control of the carrier density to the same moiré system. This ultimately enabled them to realize charged moiré excitons, which are also known as moiré trions.
"In our experiments, we measured the light emission from the heterolayers we examined," Xu explained. "By focusing on emission properties (linewidth, polarization, intensity, energy etc) as a function of carrier doping, magnetic field and temperature, we were able to identify moiré trions."
The findings could have important implications for the future development of new nanotechnology, as well as for the study of excitonic phenomena. In their future work, the team hopes to utilize moiré systems to investigate different physical phenomena.
"We showed that moiré potential can also trap charged excitons," Xu said. "Combined with the charge neutral ones, the heterobilayer can be used as a platform for studying both bosonic and fermionic many-body effects based on moiré excitons. In our next studies, we plan to study both equilibrium and non-equilibrium many body effects based on the moiré systems."
MoiHongyi Yu et al, Moiré excitons: From programmable quantum emitter arrays to spin-orbit–coupled artificial lattices, Science Advances (2017). DOI: 10.1126/sciadv.1701696
Kyle L. Seyler et al, Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers, Nature (2019). DOI: 10.1038/s41586-019-0957-1
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