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Recent valleytronics News

SnS is found to be a promising valleytronics material

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.

SnS Valleys respond to light polarization (image)

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 confirm the existence of chiral phonons in a 2D material

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.

Chiral Phonons in WSe2 (Berkeley Lab)

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 design a complete valleytronic-based logic gate

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 find a way to achieve current valley separation in graphene

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.

Valley current asymmetry in graphene

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.

NRL researchers demonstrate how one can control the degree of valley polarization in monolayer TMDs

Researchers from the US NRL laboratory have experimentally shown why different TMDs feature different degree of valley polarization. Specifically the researchers uncovered the connection between photoluminescence (PL) intensity and the degree of valley polarization.

WS2 optical excitation and PL intensity map (NRL)

The researchers used monolayer TMDs (transition metal dichalcogenides), mainly WS2 and WSe2. Samples that exhibited low PL intensity exhibited a higher degree of valley polarization. This means that if one controls the defects and nonradiative recombination sites in a monolayer TMD than once could create a material with a high or low degree of valley polarization.

Researchers prove that it is possible to create spin-valley half-metal materials

Researchers from the RAS in Russia and RIKEN in Japan have proved the existence of a new class of materials, spin-valley half-metals. This discovery could lead to devices that enable both valleytronics and spintronics.

Spin-valley half-metal image (MIPT)

In "regular" half-metals, all the electrons that participate in electric currents have the same spin - and so the current is always spin-polarized. These materials have interesting applications for spintronics devices. In the new class of materials now proven theoretically to be possible, there are two valleys present - one providing electrons, one providing holes.

A new research center in Germany to study valleytronics using graphene and other 2D materials

RWTH Aachen University and AMO GmbH launched a new joint research center with a focus on the science and applications of graphene and related 2D materials. The new center will addressing the challenges of future technology including high-frequency electronics, flexible electronics, energy-efficient sensing, photonics as well as spintronics and valleytronics.

The new center has five founding principal investigators, all members of the $1 billion Graphene Flagship project.

Researchers manage to efficiently generate long-lived valley polarization in 2D heterostructures

Researchers from the US, Japan and Korea report an efficient generation of microsecond-long-lived valley polarization in WSe2/MoS2 heterostructures by exploiting the ultrafast charge transfer processes in the heterostructure that efficiently creates resident holes in the WSe2 layer.

Ultrafast charge transfer process in the WSe2/MoS2 heterostructure

The researchers say that the valley-polarized holes exhibit near-unity valley polarization and ultralong valley lifetime. The researchers observed a valley-polarized hole population lifetime of more than 1 μs and a valley depolarization lifetime of more than 40 μs at 10 K. The researchers say that near-perfect generation of valley-polarized holes combined with the ultralong valley lifetime may open up new opportunities for novel valleytronics and spintronics applications.

Researchers demonstrate how light can be used to manipulate electron valley

Researchers from the City College of New York have demonstrated how to manipulate the electron valley property in 2D semiconductors. This could be seen as a step towards the realization of valleytronics-based logic gates.

Valley control in 2D semiconductors (CCNY)

To control the valley, the researchers used a light trapping structure called a microcavity. The microcavity gives rise to half-light-half matter quasi-particles which have the fingerprint of the valley property. A laser can be used to optically control the quasi-particles in order to access the electrons occupying specific valley.

Researchers manage to split the energy levels between valleys in a 2D semiconductor

Researchers from the University at Buffalo discovered a new way to split the energy levels between the valleys in a two-dimensional semiconductor. The researchers used a ferromagnetic compound to pull the valleys apart and keep them at different energy levels - which enables an increase in the separation of the energy in the valley by a factor of 10 compared to an external magnetic field.

Valley energy seperation on WSe2 over EuS (U of Buffalo)

The whole device is a two-layered hterostructure made from a 10-nm thick film of europoium sulfide (EuS) which is magnetic and a single layer (<1nm) layer of tungsten diselenide (WSe2) on top. The magnetic field of the bottom layer forced the energy separation of the valleys in the WSe2.