Technical / research

Researchers from Delft University of Technology demonstrated a device that generates electrical currents with a precisely controlled number of electrons at each valley. The researchers say that when electrons are squeezed through a narrow channel, they emerge as two jets which are valley polarized. By steering these jets with a magnetic field, the researchers can regulate which jet enters through a second opening, gaining control on how many electrons end up in a specific valley.

The researchers, led by Josep Ingla-Aynes, based their device on bi-layer graphene.

Researchers from the Max Born and Max Planck institutes have shown that the few cycle limit of circularly polarized light is imbued with an emergent vectorial character that allows direct coupling to the valley current. The underlying physical mechanism involves the emergence of a momentum space valley dipole, the orientation and magnitude of which allows complete control over the direction and magnitude of the valley current.

The researchers demonstrate this effect via minimal tight-binding models both for the visible spectrum gaps of the transition metal dichalcogenides as well as the infrared gaps of biased bilayer graphene.

Researchers from the US DOE Brookhaven National Laboratory, together with Northrop Grumman, have found a way to maintain valley polarization at room temperature using novel materials and techniques. 

The researchers used a chiral lead halide perovskite material (R/S-NEAPbI3). The researchers layered 500 nanometer thick flakes onto a monolayer molybdenum disulfide (MoS2), to create what is known as a heterostructure. Using a linearly polarized laser to excite the heterostructure the researchers fabricated and then measured the light that was emitted from the molybdenum disulfide TMD using a confocal microscope. They have discovered that the new material is promising for valletronics applications.

Researchers from CNRS in France demonstrated that Platinum diselenide (PtSe₂) is a promising 2D material for a terahertz (THz) range valleytronics device.

The researchers explain that PtSe₂ is promising as, unlike other transition metal dichalcogenides (TMDs), its bandgap can be uniquely tuned from a semiconductor in the near-infrared to a semimetal with the number of atomic layers. This gives the material unique THz photonic properties that can be layer-engineered. In this research, the main demonstration was that a controlled THz nonlinearity - tuned from monolayer to bulk - can be realized in wafer size polycrystalline through the generation of ultrafast photocurrents and the engineering of the bandstructure valleys. 

An international team of scientists led by a group at the University of St Andrews and the University of Manchester, report on a giant valley-selective Ising coupling in the surface layer of an intercalated transition metal dichalcogenide, V_1/3NbS₂.

Using angle-resolved photoemission spectroscopy measurements, the researchers proved the surface electronic structure of the semimetal. The researchers discovered an alternating pattern of enhancement and quenching of valley-spin polarization of the host NbS2 layers due to the intercalated Vanadium ions, equivalent to the application of a 250 T magnetic field. The researchers say that this is a major step forward in valleytronics, opening up new opportunities for the development of advanced electronic devices.

Researchers from China's Tsinghua University developed a novel material, made from a stack of 2D materials, that offers interlayer excitons, useful for valleytronics applications.

The new material is a trilayer TMD heterostructure, composed of molybdenum and sulfur, molybdenum and selenium, and tungsten and selenium. Using photoluminescence spectroscopy, the researchers confirmed the presence of interlayer excitons and described various properties and requirements of the phenomenon.

Researchers from the National University of Singapore researchers have developed an approach to account for the effect of dynamical electron-electron interactions when predicting the energy levels in valleytronic materials in the presence of a magnetic field.

The researchers predicted that Landau levels belonging to different valleys in a two-dimensional (2D) valleytronic material, monolayer tungsten diselenide (WSe₂), can be aligned at a critical magnetic field. The alignment of distinct entities, such as two laser beams, or two pillars, is a common goal in many fields of science and engineering. In the more exotic world of quantum mechanics, the alignment of quantized electronic levels can enable the creation of particles called pseudo-spinors that are useful for quantum computing applications.

Researchers from the Indian Institute of Technology Bombay (IIT Bombay) have proposed a device structure for a valley polariser which is robust, all-electrical, and can be seamlessly integrated with modern electronics. The device can be fabricated using existing fabrication techniques.

The device is based on 2D-Xene materials. A single-layer of 2-D Xene is used as the charge carrying channel. A terminal called a gate controls the electric current flowing through the channel, similar to how a gate controls the current in the modern transistor design. The gate structure, which is also used to create the valley separation, sandwiches the 2-D Xene ribbon.

Researchers from Rice University suggest that growing graphene sheets on curved surface may be a useful technique to create valleytronics devices.

The peaks and valleys in the resulting "deformed" graphene sheet would create channels that will feature small magnetic fields. It will also be a way to achieve a Hall Effect, useful for valleytronics devices.