Researchers from the University of California, Riverside,have developed a new method to read the valley indices of the dark excitons and trions. The researchers used monolayer (2D) tungsten diselenide (WSe2), a semiconductor with two distinct electronic valleys.The material hosts bright and dark excitons or trions with different spin configurations.
The researchers say that dark excitons and trions in monolayer WSe2 have much longer lifetime and better valley stability than the common bright excitons and trions - which makes them excellent candidates for valleytronic applications. But up until now there was no method to read the valley indices of the dark excitons and trions because their light emission from either valley has exactly the same energy and polarization. By identifying a measurable physical quantity that can distinguish the two valley indices of dark excitons and trions, the team was able to devise a method to read the valley indices.
The International Institute of Physics in Brazil recently uploaded this interesting talk by Stephan Roche from the ICREA and CINN who discusses valleytronics in 2D materials (such as graphene):
This talk was given as part of the IIP's 2D Materials: From Fundamentals to Spintronics workshop which took place in early October.
Researchers from Korea's Daegu Gyeongbuk Institute of Science and Technology (DGIST) discovered the formation of valley domain, which can expand valleytronics technology.
The researchers say that they have solved the stability problem inherent in valley spin in valleytronics devices by discovering the formation of valley domain in 2D molybdenum disulfide (MoS2). The team identified that a valley domain formed in an extreme nano structure can be used to store information in place of spin.
Researchers from EPFL's Laboratory of Nanoscale Electronics and Structures (LANES) developed a new way to control the valley properties of excitons and change the polarization of the light they generate.
Excitons, or electron and electron hole pairs, are created when an electron absorbs light and moves into a higher energy band. To research the excitons, the researchers used a material made from tungsten diselenide (WSe2) and molybdenum diselenide (MoSe2), and a circular polarized laser that was focused on the film.
Researchers from Penn State University developed a topological valley valve, which controls electron flow. Using electron "beam splitters", the researchers achieved high-level of electron control.
Using bilayer graphene, the researcher created electron waveguides created by gates defined with extreme precision using state-of-the-art electron beam lithography.By controlling the topology of the waveguides (the valley-momentum locking of the electrons), the researchers can control electron flow.
The US National Science Foundation (NSF) has allocated $20-25 million for a new six year program called "Enabling Quantum Leap: Convergent Accelerated Discovery Foundries for Quantum Materials Science, Engineering, and Information" (Q-AMASE-i).
Q-AMASE-i encompasses many clases of materials, includings ones that explore the paradigms or spintronics, hybrid 2D materials - and Valleytronics.
Researchers from Princeton University observed that electrons in bismuth prefer to crowd into one valley rather than distributing equally into the six available valleys. This behavior creates a type of electricity called ferroelectricity, which involves the separation of positive and negative charges onto opposite sides of a material.
The finding confirms that ferroelectricity arises naturally on the surface of bismuth when electrons collect in a single valley. This behavior could be exploited in future Valleytronics devices. The existence of six valleys in bismuth raises the possibility of distributing information in six different states.
Researchers from the University of Michigan, the University of Marburg and the University of Regensburg used circularly polarized infrared laser pulses to move electrons between valleys in a 2D material made of Tungsten and Selenium in a honeycomb lattice (similar to graphene).
These laser pulses are extremely short - just a few femtoseconds long, which results in extremely fast data switching. The researchers say that such "lightwave" computing could be millions of times faster than current computers, and be used to develop quantum computing architectures.
Researchers from Berkeley Lab discovered that Tin(II)-Sulfide (SnS) is a promising valleytronics material as its valleys have different shapes and responses to different polarizations of light. This property means that in SnS it is easy to read valleytronics data bits.
The researchers have shown that SnS is able to absorb different polarizations of light and then selectively re-emit light of different colors at different polarizations. In such a material, it is possible to concurrently access both the usual electronic and valleytronic degrees of freedom.
Researchers from the DoE Lawrence Berkeley National Laboratory have proved the existence of chirac phonons - a shaking motion in the structure of 2D material that possesses a naturally occurring circular rotation. This rotation may mean that the material is promising for data-storage based on valleytronics.
The researchers used tungsten diselenide (WSe2), a material that has an unusual ability to sustain special electronic properties that are far more fleeting in other materials. With this new discovery of the chirac phonons, the researchers believe that controlling the rotation direction could prove to be a stable mechanism to carry and store information.
