They are drawn in by the moiré pattern – a strange, beautiful and mysterious optical phenomenon. It revealed a stunning choreography of interlayer excitons that zip around with remarkable fluidity even at cryogenic temperatures. When you stack and rotate two images with tessellating concepts, a beautiful pattern appears. It generates a trippy undulating pattern in the form of a wave shape that appears to ripple over the stitched together graphic. The complex structure is a result of the interlayer coupling between two layers of transition metal dichalcogenides (TMDs). This interaction produces a special “perfect storm” phenomenon requiring very little energy to begin moving. Although scientists are currently studying this phenomenon, they hoped to gain new insights into the role of the moiré pattern in governing exciton transport and quantum coherence.
The Formation and Characteristics of Moiré Patterns
The characteristic moiré pattern occurs when two sheets of transition metal dichalcogenides (TMDs) are precisely aligned. Only the tiniest arc and/or twist among the sheets produces this optical wonder. This interference produces an astonishing never-seen-before wave-like symmetry. That’s why people have come to call it a “seascape,” and why it glides fluidly with so little energy expenditure. This shift in pattern depends on the angle of incidence and temperature. Its properties change based on the orientation of the layers or the speed at which they cool.
"It takes very little energy to make this moiré potential move, so the moiré is moving around exactly like a stormy sea," explained Antonio Rossi, highlighting the dynamic nature of this phenomenon.
The beauty of the moiré pattern is not entirely skin deep. It’s creating waves in the field of quantum mechanics. It behaves like a low-temperature quasiparticle known as a phason. This efficient property creates a pathway for interlayer excitons (IX) to roam, despite looking like they are ball and chained inside the valleys of the landscape.
The Role of Interlayer Excitons
Interlayer excitons, or IXs for short, are quasiparticles that are intrinsic to the moiré pattern dynamic. These excitons are formed as a result of direct optical excitation of electrons within the TMD layers. Once established, though, they’re left weaving through the complex terrain produced by the moiré pattern. Fascinatingly, one could expect these excitons to remain still due to the trapping potential of the moiré valleys themselves. Science has proved that in reality they don’t stay put at all.
"You have the (interlayer) exciton surfing the moiré and moving around," stated Antonio Rossi, illustrating how these excitons are able to traverse their environment despite apparent constraints.
"It's kind of carrying the exciton, in a way," added Rossi, emphasizing the role of the moiré pattern in facilitating movement.
This counterintuitive mobility is explained by the peculiar mechanical properties of the moiré pattern itself. Sea” stormy sea, allowing excitons to maneuver with extraordinary fluidity. This motion challenges standard notions of energy localization at low temperatures.
Ongoing Research and Implications
It’s the subject of intense scientific research at present, specifically looking at how moiré patterns impact exciton movement. They are all doing important work to get at the underlying mechanics and understand how to apply them. Developing a better understanding of these patterns might unlock powerful new techniques for quantum computing. These innovations will further enable other advanced technologies dependent on quantum stability.
"We showed that even at very cold temperatures, energy and information are not as localized as you might expect," noted Archana Raja. "This happens because of a special 'mechanical property' of the moiré pattern."
"Jonas' work made it so we could seamlessly collect luminescence spectra, image, and lifetime (data), all of which enabled us to extract the diffusivity (movement) of the excitons," Raja added, underscoring the importance of comprehensive data collection in this research.
The broader impacts of this research go beyond simply advancing theoretical understanding, with promising applications that could shape future advancements in materials science and nanotechnology. Now, scientists can take advantage of moiré patterns’ unique properties. This might help us create more efficient systems for transferring energy and processing information at the quantum level.