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.
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.
Researchers from the SUTD-MIT International Design Center at Singapore University of Technology and Design have demonstrated a concrete working design of valleytronic-based logic gate capable of performing all 16 types of boolean logic operators. This logic gate can also perform logically-reversible computing - useful in many applications ranging from cryptography to signal processing and quantum computing.
To achieve this logic gate, the researchers used a 2D-material (Phosphorene) in combination with a topological Weyl/Dirac semi-metal thin films. The valleytronics gate encodes extra bits of information in the valley polarization of the computational output to preserve logical-reversibility.
Researchers from Ohio University have found a simple yet effective way to achieve current valley separation in graphene. The idea is based on inversion symmetry, or the creation of properly oriented obstacles that break an important symmetry of the graphene crystal.
This is a theoretical work, but the researchers say that the results could enable seperating and controling valley currents in graphene in real experiments which will hopefully lead to the utilization of graphene in future valleytronics devices.