# Working with atomic units

1. Feb 4, 2012

### zakk87

I'm having some troubles understanding the unit used in solid state physics. In a paper I read

$$\Lambda a \sim 1$$

where $\Lambda$ is a momentum cutoff and $a$ is the lattice spacing of a crystal. Questions:

1) What kind of units are customarily used in solid state physics scientific articles? Can I be confident that they are atomic units?

2) The aforementioned equation is not correct as far as the units of measure are concerned. If this was solid state physics, I would say that one could set the speed of light and the Planck constant to 1 and make the equation correct. However in a low energy treatment in solid state physics, I don't see the point in using the speed of light or the Planck constant, and making the physics of the system dependent upon these quantities.

The momentum p can be written as $$p=\hbar k$$ where k is the wavevector.