Observation of intervalley transitions can boost valleytronic science and technology

Science Daily  May 15, 2020 When monolayer WSe2 absorbs a photon, a bound electron can be freed in a valley, leaving behind a hole resulting in an exiton. This is called an intravalley exciton which can emit light. The law of momentum conservation, however, forbids an electron and a hole in opposite valleys from recombining directly to emit light. As a result, intervalley excitons are “dark” and hidden in the optical spectrum. An international team of researchers (USA – UC Riverside, Taiwan, Japan) found that although the intervalley excitons are intrinsically dark, they can emit circularly polarized light. The optically […]

Giving valleytronics a boost

Science Daily  October 28, 2019 Development of valleytronics requires stable valley states and easy identification of the valley indices. An international team of researchers (USA- UC Riverside, Japan, Taiwan) have shown that dark excitons and trions in monolayer WSe2 have much longer lifetime and better valley stability than the common bright excitons and trions, therefore, serve as excellent candidates for valleytronic applications. Until now no method could read the valley indices of the dark excitons and trions because their light emission from either valley has exactly the same energy and polarization, making the two valleys indistinguishable from each other. They […]

Valleytronics in a monolayer semiconductor at room temperature

Nanowerk  October 24, 2019 Valleytronics is very attractive for future electronic devices and quantum computing technology. However, the phonon-assisted intervalley scattering accelerates dramatically when temperature is increased, resulting in volatile valley states and significantly reduced handedness of far-field photoluminescence at room temperature. A team of researchers in the US (UT Austin, University of Pennsylvania) addressed these issues by manipulating strong light-matter interactions between valley excitons, and a purpose-designed plasmonic chiral metamaterial. In demonstration they were able to actively and reversibly tune and turn ON/OFF the manipulation. These results provide a new way to control quantum information carriers in 2D materials. […]

‘Valley states’ in this super-thin material could potentially be used for quantum computing

Phys.org September 23, 2019 Past research has shown that applying a magnetic field can shift the energy of the valleys in opposite directions, lowering the energy of one valley to make it “deeper” and more attractive to electrons, while raising the energy of the other valley to make it “shallower,” A team of researchers in the US (SUNY Buffalo, University of Nebraska) showed that the shift in the energy of the two valleys can be enlarged by two orders of magnitude if we place a thin layer of magnetic europium sulfide under the tungsten disulfide. After that when they applied […]

Excitons pave the way to more efficient electronics

Nanowerk  January 4, 2019 An international team of researchers (Switzerland, Japan) combined tungsten diselenide with molybdenum diselenide to reveal new properties with an array of possible high-tech. By using a laser to generate light beams and slightly shifting the positions of the two 2D materials to create a moiré pattern, they were able to use excitons to change and regulate the polarization, wavelength and intensity of light. By manipulating the “valley,” of the exiciton, it can be leveraged to code and process information at a nanoscopic level. Linking several devices that incorporate this technology would give us a new way […]

On the cusp of valleytronics

Nanowerk  November 30, 2018 According to researchers in Singapore information can be transmitted by controlling an electron’s association with a valley — a manipulation that can be achieved using electric fields, magnetic fields and circularly polarised light. As the valley is a property of the whole material, the valley states are destroyed only if the material is significantly modified or ceases to exist. Therefore, encoding information onto valley states should be more enduring due to the unique coupling of electron spin to valley. They are engineering a number of new and useful 2D semiconductors for this technology by adjusting their […]

Light could make semiconductor computers a million times faster or even go quantum

Phys.org   May 10, 2018 An international team of researchers (Germany, USA – University of Michigan) has demonstrated that a single layer of tungsten and selenium in a honeycomb lattice produces a pair of electron states known as pseudospins that can encode the 1 and 0. They prodded electrons into these states with quick pulses of infrared light. The initial pulse has its own spin, known as circular polarization, that sends electrons into one pseudospin state. Pulses of light that don’t have a spin can push the electrons from one pseudospin to the other—and back again. The work opens the door […]

‘Valleytronics’ discovery could extend limits of Moore’s Law

Science Daily  May 1, 2018 An international team of researchers (USA – UC Berkeley, Lawrence Berkeley National Laboratory, Singapore, China) has shown that tin(II) sulfide is able to absorb different polarizations of light and then selectively reemit light of different colors at different polarizations. This is useful for concurrently accessing both the usual electronic and the material’s degrees of freedom. SnS possesses selectivity at room temperature without additional biases apart from the excitation light source. With this finding, researchers will be able to develop operational valleytronic devices, which may one day be integrated into electronic circuits. The unique coupling between […]