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A Weyl semimetal is a solid state crystal whose low energy excitations are Weyl fermions that carry electrical charge even at room temperatures. [ 11 ] [ 12 ] [ 13 ] A Weyl semimetal enables realization of Weyl fermions in electronic systems. [ 9 ]
For example, a solid with two identical phonons does not have exactly twice the excitation energy of a solid with just one phonon, because the crystal vibration is slightly anharmonic. However, in many materials, the elementary excitations are very close to being independent.
A chiral phenomenon is one that is not identical to its mirror image (see the article on mathematical chirality). The spin of a particle may be used to define a handedness , or helicity, for that particle, which, in the case of a massless particle, is the same as chirality.
Specific heat, the heat capacity per unit mass, describes the energy required to change the temperature of a sample. The low-temperature electronic specific heat of Dirac matter is C ( T → 0 ) ∼ T d {\displaystyle C(T\to 0)\sim T^{d}} which is different from C ( T → 0 ) ∼ T {\displaystyle C(T\to 0)\sim T} encountered for normal metals ...
Phonon polaritons only result from coupling of transverse optical phonons, this is due to the particular form of the dispersion relation of the phonon and photon and their interaction. Photons consist of electromagnetic waves, which are always transverse. Therefore, they can only couple with transverse phonons in crystals.
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.
In quantum field theory, a chiral gauge theory is a quantum field theory with charged chiral (i.e. Weyl) fermions. For instance, the Standard Model is a chiral gauge theory. For topological reasons, chiral charged fermions cannot be given a mass without breaking the gauge symmetry, which will lead to inconsistencies unlike a global symmetry.
In physics, particularly in quantum field theory, the Weyl equation is a relativistic wave equation for describing massless spin-1/2 particles called Weyl fermions. The equation is named after Hermann Weyl. The Weyl fermions are one of the three possible types of elementary fermions, the other two being the Dirac and the Majorana fermions.