Kimi Chen In physics terms the difference between spintronics and valleytronics is that spintronics is (physics) the storage and transfer of information using the spin state of electrons as well as their charge while valleytronics is (physics) a proposed equivalent of electronics utilizing (valleys) in the valence band or conduction band structure of some semiconductors or insulators that possess multiple valleys, such as graphene, carbon nanotubes, bismuth, dichalcogenides, diamond or silicon.

Electrons in graphene carry not only electric charge and information about spin, but also information about the so-called pseudospin. Research of the last of these properties will enable the development of a completely new branch of technology - valleytronics (analogous to electronics and spintronics). Valleytronics and spintronics are essentially similar in that information is coded in a quantum number as opposed to charge for conventionnal electronics. They differ in the quantum number used (i.e. Spin or Valleys).

"Valleytronics" – a new type of electronics in diamond. An alternative and novel concept in electronics is to utilize the wave quantum number of the electron in a crystalline material to encode information. In a new article in Nature Materials, Isberg propose using this valley degree of freedom in diamond to enable valleytronic information processing or as a new route to quantum computing.

A potential avenue to quantum computing currently generating quite the buzz in the high-tech industry is “valleytronics,” in which information is coded based on the wavelike motion of electrons moving through certain two-dimensional (2D) semiconductors. Now, a promising new pathway to valleytronic technology has been uncovered by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab). Like spintronics, valleytronics offer a tremendous advantage in data processing speeds over the electrical charge used in classical electronics. Quantum spin, however, is strongly linked to magnetic fields, which can introduce stability issues. This is not an issue for quantum waves.

There are many definitions, I hope I have helped to clarify this new concept and its differences.

References:

Article Valleytronics: Opportunities, Challenges, and Paths Forward

https://arxiv.org/ftp/arxiv/papers/1212/1212.6376.pdf

http://scienceinpoland.pap.pl/en/news/news%2C26500%2Celectronics-and-spintronics-are-not-end-time-valleytronics.html

https://newscenter.lbl.gov/2015/01/26/new-pathway-to-valleytronics/

Oreci Escobar Da Silva Thanks for your reply. Can you elaborate pseudospin and berry curvature in easy words?

Kimi Chen Certain scientific concepts are often difficult to translate into simple words because they carry a huge bag of new concepts, but hopefully this answer gives you a light on pseudospin and berry curvature.

The concept of pseudospin - From New perspectives for Rashba spin–orbit coupling A. Manchon, H. C. Koo, J. Nitta, S. M. Frolov & R. A. Duine Nature Materials 14, 871–882 (2015) doi:10.1038/nmat4360

Pseudospin in materials. Although spin is the quantized intrinsic angular momentum of a particle, many other physical quantities can act as an effective spin-1/2, which is referred to as pseudospin. This concept was originally introduced by Heisenberg to describe the structure of the atomic nucleus as composed of neutrons and protons, which he modelled as two states of the same particle147. In this context, a pseudospin is a coherent superposition of two quantum states and is described in terms of Pauli matrices for spin-1/2, σ = (σx, σy, σz). Although Nambu pseudospin was introduced decades ago to describe quasiparticles in superconductors, recent developments in the physics of SO-coupled transport have identified new degrees of freedom that can be accounted for within the pseudospin language89. In hexagonal 2D diamonds, the pseudospin is composed of the sublattices92, whereas in TMDC it describes the valence and conduction bands of the transition metal95. In van der Waals bilayers, when the layer index is a good quantum number, a layer pseudospin can also be identified148. Finally, in cold-atom systems, the spin-1/2 pseudospin is defined by two hyperfine split states that can be, for example, coherently coupled by a laser149.The concept of pseudospin is useful for predicting and interpreting the transport properties of the various systems mentioned above, in particular when a Rashba-type pseudospin–orbit coupling is present89. Nonetheless, it has an important limitation: the nature of the pseudospin (such as sublattice or layer index) is a material property — not an intrinsic property of the carrier, like the spin degree of freedom (except in the case of cold atoms). Therefore, it may not be continuous at the interfaces between different materials148.Pseudospin–orbit coupling in cold atoms. To exemplify the use of the pseudospin concept, let us consider a simple example of cold atoms. We imagine that two atomic hyperfine states (Ψ↑ and Ψ↓, selected from a large integer-spin hyperfine multiplet), representing the two states of the pseudospin, are coupled by Raman lasers. The single-particle Hamiltonian is then given by

•  Equation (4)

Where Ω is determined by the strength of the lasers (chosen to point along the x direction) and kp is the photon wavevector. The Zeeman splitting Δ is controlled by the external magnetic field, and m is the mass of the atoms. We have ignored motion in the z direction, which is justifiable as long as the confining potential is tight in this direction.The Schrödinger equation for the atoms, ĤΨ = EΨ, with Ψ = (Ψ↑(x, y), Ψ↓(x, y)), is now rotated according to Ψ = Qϕ. Here Q is the 2 × 2 matrix that diagonalizes the spin part of the Hamiltonian such that

•  Equation

The kinetic-energy part of the Schrödinger equation transforms according to

•  Equation

The laser field gives Q = Q(x, y), which leads to terms that are linear in momentum in the Schrödinger equation for ϕ. One of these terms is a pseudo-SO coupling γσx(∂/∂x) ∝ γσxpx, with γ = ħkpΩ/2m√(Ω2 + Δ2). The Rashba pseudo-SO coupling can be engineered by employing more involved laser-coupling. To view the equations and the original text, please use the following link:http://www.nature.com/nmat/journal/v14/n9/box/nmat4360_BX3.html

Rereference: https://www.researchgate.net/post/What_is_pseudospin

The concept of berry curvature - A “Berry phase” is a phase angle (i.e., running between 0 and 2π) that describes the global phase evolution of a complex vector as it is carried around a path in its vector space. It can also be referred to as a “geometric phase” or a “Pancharatnam phase,” the latter after early work by Pancharatnam (1956). The concept was systematized and popularized in the 1980s by Sir Michael Berry, notably in a seminal paper (Berry, 1984), and by Berry and others in a series of subsequent publications that are well represented in the edited volume of Wilczek and Shapere (1989). A formal discussion of Berry phases and related concepts (fiber bundles, connections, Berry curvatures, etc.) can be found in modern texts on topological physics such as those by Frankel (1997), Nakahara (2003), and Eschrig (2011). Since then, Berry phases have found broad application in diverse realms of science including atomic and molecular physics, classical optics, wave mechanics, and condensed-matter physics. Then the Berry curvature Ω(λ) is simply defined as the Berry phase per unit area in (λx, λy) space.

Reference: https://www.physics.rutgers.edu/grad/682/textbook/ch-3.pdf

Reference Image: https://pubs.rsc.org/en/content/articlelanding/2016/nr/c6nr01949h/#!divAbstract

Oreci Escobar Da Silva Thanks a lot.

The difference between spintronics and valleytronics that spintronics is the storage and transfer of information using the spin state of electrons as well as their charge while valleytronics is a proposed equivalent of electronics utilizing in the valence band or conduction band structure of some semiconductors or insulators that possess multiple valleys, such as graphene, carbon nanotubes, bismuth, dichalcogenides, diamond or silicon.