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Weyl spinors are a solution to the Dirac equation derived by Hermann Weyl, called the Weyl equation. [3] For example, one-half of a charged Dirac fermion of a definite chirality is a Weyl fermion. [4] Weyl fermions may be realized as emergent quasiparticles in a low-energy condensed matter system.
An acoustic metamaterial, sonic crystal, or phononic crystal is a material designed to manipulate sound waves or phonons in gases, liquids, and solids (crystal lattices).By carefully controlling properties such as the bulk modulus β, density ρ, and chirality, these materials can be tailored to interact with sound in specific ways, such as transmitting, trapping, or amplifying waves at ...
The ground state, also called the "vacuum state", is the state composed of no phonons. Hence, the energy of the ground state is 0. Hence, the energy of the ground state is 0. When a system is in the state | n 1 n 2 n 3 … , we say there are n α phonons of type α , where n α is the occupation number of the phonons.
Solids are made of only three kinds of particles: electrons, protons, and neutrons. None of these are quasiparticles; instead a quasiparticle is an emergent phenomenon that occurs inside the solid. Therefore, while it is quite possible to have a single particle (electron, proton, or neutron) floating in space, a quasiparticle can only exist ...
The concept goes back to Majorana's suggestion in 1937 [2] that electrically neutral spin- 1 / 2 particles can be described by a real-valued wave equation (the Majorana equation), and would therefore be identical to their antiparticle, because the wave functions of particle and antiparticle are related by complex conjugation, which leaves the Majorana wave equation unchanged.
While the Weyl equation was originally derived for odd spatial dimensions, the generalization of a 3D Weyl fermion state in 2D leads to a distinct topological state of matter, labeled as 2D Weyl semimetals. 2D Weyl semimetals are spin-polarized analogues of graphene that promise access to topological properties of Weyl fermions in (2+1)-dim ...
The three first are Type-I Weyl semimetals, the last one is a Type-II Weyl semimetal. In quantum mechanics , Dirac cones are a kind of crossing-point which electrons avoid , [ 8 ] where the energy of the valence and conduction bands are not equal anywhere in two dimensional lattice k -space , except at the zero dimensional Dirac points.
[1] [7] Lehmann was the first to coin the term liquid crystal. [8] Studies in liquid crystals soon blossomed, and in 1922 Georges Friedel created the classification system of liquid crystals still used today. In this system, he named the chiral variety of liquid crystals cholesteric, as they were discovered from a cholesterol derivative. [5] [9]