Why Use the Dirac Equation for Graphene Instead of the Schrödinger Equation?

  • Level: Graduate 
  • Thread starter Thread starter jamie.j1989
  • Start date Start date
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
2 replies · 2K views
jamie.j1989
Messages
76
Reaction score
0
Hi, I'm doing a project on graphene and don't really understand why we use the Dirac equation instead of the Schrödinger equation. The fermi velocity of electrons in graphene is not relativistic, I know the particles are considered as quasiparticles but don't see how this changes things. My only reasoning is that the effective mass is zero and the 1/m dependence in the Schrödinger equation is incompatible with this? Thanks.

Scrodinger equation

$$i\hbar\frac{\partial}{\partial{t}}\psi({\textbf{r},t})=\left[-\frac{\hbar^2}{2m}\nabla^2V(\textbf{r})+E\right]\psi({\textbf{r},t})$$

Dirac equation

$$\left[\gamma^{\mu}\partial_{\mu}+\frac{c}{\hbar}m\right]\psi(\textbf{r},t)=0$$
 
Physics news on Phys.org
Hi jamie.j1989, I am not sure what aspects of graphene you are investigating, but for example the conductance of graphene is very good, which translates to very fast moving electrons (definitely within the range where we see relativistic effects). Also the fermi velocity is only relevant at 0K, so for temperatures above that the velocities of the fastest electrons will exeed the fermi velocity.
 
jamie.j1989 said:
Hi, I'm doing a project on graphene and don't really understand why we use the Dirac equation instead of the Schrödinger equation. The fermi velocity of electrons in graphene is not relativistic, I know the particles are considered as quasiparticles but don't see how this changes things.

The fundamental equation for graphene is the Schroedinger equation. However, an equation with the form of the Dirac equation "emerges" from the Schroedinger equation as an excellent approximation at low energy. The "speed of light" in the equation with the form of the Dirac equation is not the speed of light. It is ~10^6 m/s.
http://arxiv.org/abs/cond-mat/0509330
http://www.physics.upenn.edu/~kane/pedagogical/295lec3.pdf
 
Last edited:
  • Like
Likes   Reactions: bhobba