Emergence of Excitonic Mott Insulator State in Moiré Superlattice

November 27, 2023

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Authored by Ingrid Fadelli from Phys.org, this article discusses the phenomenon when a negatively charged electron and a positively charged hole, after being excited by light, remain bound together. They create states called excitons which affect materials' optical properties, paving the way for various tech developments.

Scientists from renowned institutes worldwide - Rensselaer Polytechnic Institute, Imperial College London, University of California Riverside, Carnegie Mellon University, have been researching the creation of excitons and identifying new materials promising for optoelectronic applications. Their study has been published in Nature Physics.

The team presents evidence of an excitonic Mott insulator state in a WSe2/WS2 based moiré superlattice. This lattice is formed when two atomic layers are overlaid with a slightly different periodicity, leading to a periodic interference pattern. According to Sufei Shi, a researcher involved in the study, the interaction between electron and electron correlation was found to be strong in this superlattice structure.

The team foresees a possibility of using this strong exciton correlation to give rise to new quantum states of excitons, which are bosons and differ from fermions (electrons). Shi and others have been examining moiré superlattices due to their unique structures that are intriguing for manipulating excitons. The structures comprise two or more atomically thin crystals stacked together, generating a 'lattice mismatch'.

The current paper focuses on further exploring this structure's potential for realizing quantum states of excitons. Shi explained that their experiment primarily utilized optical spectroscopy techniques, particularly photoluminescence (PL) spectroscopy.

Shi's team's experiments provided evidence of an exciton-driven Mott insulator state in the WSe2/WS2 structure. This state could contribute significantly to quantum systems studies and development. The findings show that the moiré superlattice has strong exciton correlation, making it possible to construct quantum states from many-body Hamiltonian of bosons.

This research strengthens previous studies and emphasizes the WS2/WSe2 moiré superlattice's potential for creating new correlated states. The excitonic Mott insulator state discovered could be instrumental in future research and other works leveraging the same experimental platform.

Shi mentioned that their future research aims to explore this excitonic Mott insulator state's valley-spin and use their new understanding in constructing new quantum state and performing quantum simulations based on excitons or exciton-electron mixture.

Further information about the study can be found in their paper titled 'Valley-polarized excitonic Mott insulator in WS2/WSe2 moiré superlattice,' published in Nature Physics (2023).

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