In this type of moiré superlattice, the atoms in each layer are arranged in hexagons. (Credit: Tschub/Shutterstock)

As reported in Nature Physics, a Berkeley Lab-led team of physicists and materials scientists were the first to unambiguously observe and document the unique optical phenomena that occur in certain types of synthetic materials called moiré superlattices. The new findings will help researchers understand how to better manipulate materials into light emitters with controllable quantum properties.

Moiré superlattices are made by layering sheets of single-atom-thick materials on top of one another in precise configurations to create a larger and more complex overall pattern. In these arrangements, the otherwise simple composite materials display intriguing behavior.

For example, recent studies from the same team showed that moiré superlattices made with three layers of graphene sandwiched in between layers of boron nitride can act as an exotic insulator and a high-temperature superconductor.

In the current study, Berkeley Lab graduate student researcher Emma Regan and her colleagues used two highly sensitive spectroscopy approaches to examine the excitons (bound pairs of electrons and electron-holes, which occur in semiconductive materials) across the layers of a moiré superlattice formed by tungsten disulfide and tungsten diselenide.

“Our work provides needed clarity on how the excitons in moiré superlattices can exist in different states,” said Regan. “And now we know a straightforward way to create perfect arrays of interlayer excitons with distinct optical properties, which can serve as light emitters in next-generation electronic devices.”