ELI5: Explain Like I'm 5

Particle in a one-dimensional lattice (periodic potential)

Okay, imagine you have a toy car that can only move in a straight line. Now imagine putting a bunch of little bumps along the road that the car has to drive over. These bumps are like little hills or valleys that make it harder for the car to move smoothly.

Now, let's say that our toy car is actually a tiny particle that we can't see, and the bumps on the road are like a one-dimensional lattice. This lattice is made up of a bunch of little bumps, almost like a tiny mountain range that our particle has to move through.

When the particle moves through this lattice, it can only move from one bump to the next. Imagine jumping from one hill to the next hill, like hopping from one step to the next step on a staircase. This is how the particle moves through the lattice.

But here's where things get really interesting. The lattice isn't just a random bunch of bumps - it's actually a periodic potential. What does that mean? Well, imagine that you have a piece of music that's repeating over and over again. Each time the music repeats, it sounds exactly the same. That's what "periodic" means - it's something that repeats itself over and over again.

So, the periodic potential we're talking about is like a repeating pattern of bumps. Each bump is the same size and shape, and they repeat over and over again. It's like the particle is jumping from one step to the next on an infinite staircase that never ends.

This might sound strange, but it has some really interesting effects on the particle's behavior. When the particle moves through the lattice, it can actually get trapped between two bumps. It's like getting stuck in a small valley between two hills. But, because the potential is periodic, the particle can also tunnel through to the other side of the bump. It's like magically appearing on the other side of the hill, without actually having to climb over it.

This jumping and tunneling behavior of the particle in the one-dimensional lattice is the basis for a lot of really interesting physics. It can be used to explain how electrons move through certain materials, or how light interacts with certain crystals. But, at its most basic level, it's just like a tiny particle hopping along a bumpy one-dimensional road, over and over again.