Recent experimental work has brought impressive progress in our ability to comprehend spin-selective transport through tungsten diselenide (WSe2), a two-dimensional semiconductor. The work was led by En-Min Shih and his team, with Qianhui Shi serving as co-first author and Cory Dean as the lead principal investigator. Their research inquiries into the effects of strong magnetic fields on Landau levels, discrete energy levels that emerge in 2D materials. These results open up a promising new avenue to developing small, precise, energy-efficient spintronic devices. These new devices control not just the charge, but the spin, of electrons.
The experimentalists were interested in exploring the odd and unusual properties that occur at very high magnetic fields, where Landau levels form perfectly spaced quantum states in WSe2. Conventional two-dimensional materials would always show a repeating pattern of spin-up and spin-down energy levels. In WSe2, one can fill up to six spin-up Landau levels before a spin-down level shows in the spectrum. This unique feature creates exciting prospects for new technology applications.
The Role of Landau Levels
Landau levels appear in any two-dimensional material placed under intense magnetic fields. Understanding these materials is vital to understanding the electronic properties and transport of charges. Our research team worked to thoroughly study these higher levels in WSe2, uncovering a truly remarkable nature rarely seen in other materials.
“In most systems, the Landau level sequence consists of alternating spin-up and spin-down levels. So, if you add electrons to these levels to fill them up, the first level has all spins pointing up, then in the second level, all spins point down, and so on. In this regard, WSe2 is exceptionally unique where several levels in a row can all have the same spin before you encounter the opposite spin state.”
The non-intuitive implications of Landau levels have far-reaching applications beyond condensed matter physics. Their work offers new windows into how electron spins couple to each other—and how they can be controlled, in turn, for real-world applications. Their research reveals new and promising ways to manipulate electron spins with light, rather than magnetic fields. This revolutionary advancement represents the biggest step yet in the field of spintronics.
Spintronics and Its Applications
These developments have advanced the field of spintronics, or spin electronics, which use the electric charge of electrons. It takes advantage of their intrinsic angular momentum, or spin. The combined data storage and energy functions open up exciting opportunities for creating new types of technology, particularly in data storage and processing.
En-Min Shih elaborated on the importance of spin in modern technology:
“Spin is a fundamental quantum property of electrons, which—in a simplified picture—can be thought of like a tiny internal compass needle pointing either ‘up’ or ‘down.’”
The research team demonstrated that when mobile electron carriers in WSe2 have spins that match those in a nearby magnet, electrical conductivity increases significantly. On the flip side, when the spins don’t cooperate, or line up, conductivity fades as robust Coulomb interactions block charge movement.
This method would not only make the manufacturing process easier, but increase overall efficiency for applications to come. The possibility of manipulating spins with purely optical methods rather than requiring the use of magnetic fields is another area where new opportunities for innovation are unlocked.
“While existing technology works well, it is challenging and expensive to make, primarily because you have to integrate different materials into complicated structures. In our work, we asked a simple question: Can we achieve spin-selective transport—where only electrons with a certain spin state can move—using just a single, non-magnetic material?”
The members of the research team agree that the results of their work are steps toward improved performance of next-generation spintronic devices. They proposed groundbreaking ideas, such as valley pseudospin. This idea represents the fundamental way that electrons couple to the atomic lattice of materials. This makes it significantly more complicated with respect to how that information should be processed and stored.
Future Implications and Research Directions
One connection the study revealed was a pretty interesting one. Interestingly, the dynamics of currents propagating through the Shear Instability induced maximum Landau level closely replicates that found in magnetic memory devices. The researchers concluded that as long as carriers are in line with the dominant spin group, they are free to travel unencumbered. This alignment with highest filled levels of lesser energy facilitates high conductance. In stark contrast, carriers in the majority spin group undergo localization, resulting in an abrupt decrease in conductivity.
While this line of investigation is still unfolding, it’s incredibly promising. It has the potential to fundamentally change how electronic devices record and compute knowledge. With its versatility in different environments, WSe2 is paving the way to more advancements in electronics.
“This could be significant for future technology opportunities since valley pseudospin may be manipulated with optical rather than magnetic fields.”
Moreover, the study revealed that the behavior of currents flowing through the highest Landau level resembles that found in magnetic memory systems. The researchers observed that when carriers belong to the majority spin group—matching that of lower energy filled levels—they move freely and contribute to high conductance. In contrast, carriers in the minority spin group experience localization, leading to a sharp drop in conductivity.
“When these carriers belong to the majority spin group (same spin as the lower energy ‘filled’ levels), they can move freely and contribute to significant conductance; when they are in the minority spin group (opposite spin to the filled levels), their motion is effectively suppressed—they become localized, and conductivity drops sharply,” – En-Min Shih.
As this line of investigation continues, it holds promise for revolutionizing how information is stored and processed in electronic devices. The adaptability of WSe2 under varying conditions establishes it as a key player in future electronic innovations.