Technical / research

Researchers discover ferro-valleytricity in five-layer graphene

Researchers from MIT, Harvard and Japan's NIMS have discovered that in a five-layer graphene arranged in a rhombohedral pattern, a rare state occus, a multi-ferroic state, in which the material exhibits both unconventional magnetism and an exotic type of electronic behavior, which the team has named "ferro-valleytricity".

Valleytronics in five-layer graphene - MIT, Harvard, NIMS photo

The first time that ferro-valleytricity and unconventional magnetism are observed, in five layers of graphene. This is not occurring in single-layer graphene (or in two, three, or four layers). This state could lead to a future valleytronics device, a fast storage device that will be highly efficient, as the domains in such a device can be switched very fast with a very low-power electric field. 

Read the full story Posted: Oct 20,2023

Researchers use perovskites and 2D TMDs to create a promising valleytronics material

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.

Read the full story Posted: Sep 10,2023

Researchers show that Platinum diselenide is a promising 2D material for terahertz valleytronics

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. 

Read the full story Posted: Sep 07,2023

Researchers discover giant valley-selective Ising coupling in the surface layer of an intercalated transition metal

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, V1/3NbS2.

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.

Read the full story Posted: Feb 23,2023

Researchers develop a trilayer TMD heterostructure with interlayer excitons

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.

Read the full story Posted: Jun 29,2022

Researchers developed an approach to align Landau levels of different valleys in 2D materials

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.

Read the full story Posted: Jun 16,2022

IIT Bombay researchers developed a valley polariser based on 2-D Xenes

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.

Read the full story Posted: May 19,2022

Researchers show it is possible to realize a valleytronics device in pristine graphene

Researchers from Germany (Max-Born Institute) and India (IIT Bombay) have shown that it is possible to realize a valleytronics device in pristine graphene.

Reading and writing valley-selective electron excitations in graphene (image)

Graphene (and other graphene-like systems) feature an extra degree of electron freedom, or valley pseudo-spin. This has interesting potential in valleytronics applications, but the implementation of valleytronics ideas has been so far limited to gapped graphene-like semiconducting 2D materials, most commonly transition metal dichalcogenides, and has never been attempted in pristine graphene, because graphene monolayers have zero bandgap, zero Berry curvature, and thus nearly identical valleys,.

Read the full story Posted: Jul 19,2021

Researchers demonstrate how few-cycle linearly polarized pulses can induce a high degree of valley polarization

Scientists from several research institutes in Germany and the UK have demonstrated that few-cycle linearly polarized pulses can induce a high degree of valley polarization.

few-cycle linearly polarized pulses can induce a high degree of valley polarization

The mechanism to induce such polarization does not rely on the optical selection rules, and therefore can be in principle used in inversion symmetric materials, such as TMD bilayers or graphene. This could enable the design of ultrafast valleytronic devices.

Read the full story Posted: Feb 26,2021