Direct Link Discovered Between Sample Quality & Valley Polarization

Wikimedia Commons

Wikimedia Commons

Scientists from the United States Naval Research Laboratory (NRL) have discovered a new link that connects sample quality and the degree of valley polarization in monolayer transition metal dichalcogenides (TMDS). This direct link could have enormous use in future applications in the fields of electronic and optoelectronic technologies.

A valley describes a region in an electronic band structure. This region is where electrons and holes are localized; valley polarization is the ratio of the population of the valley. A wide variety of technologies, from cellphone batteries to computer chip transistors) depend on the charge of an electron and its ability to move through material. Some materials are more adaptable; in monolayer TMDs, the electrons can be placed in specific electronic valleys thanks to optical excitation.

“The development of TMD materials and hybrid 2D/3D heterostructures promises enhanced functionality relevant to future Department of Defense missions. These include ultra-low power electronics, non-volatile optical memory, and quantum computation applications in information processing and sensing.”

Berend Jonker, Ph.D., principal investigator of the program

Scientists hope to use the spin or valley population, as opposed to only the charge, for information storage. The population could also be used to perform logic operations in the developing fields of spintronics and valleytronics. Engineers have already come up with innovative new products, such as the magnetic random access memory.

Researchers primarily focused their efforts on TMD monolayers like W2 and WSe2. These have high optical responsivity; upon further investigation, scientists discovered that those samples with low photoluminescence intensity showed a high degree of valley polarization. This could provide scientists with a way to engineer valley polarization, thanks to a controlled introduction of nonradiative recombination sits and defects.

“A high degree of valley polarization has been theoretically predicted in TMDs yet experimental values are often low and vary widely. It is extremely important to determine the origin of these variations in order to further our basic understanding of TMDs as well as advance the field of valleytronics.”

Kathleen McCreary, Ph.D., lead author of the study

The interdisciplinary team is eager to further test the limits of this connection, and to see what other fields could benefit from this important discovery.

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