Are there any good books that give good mathematical/physical background to the workings of the Hofstadter's Butterfly? I'd appreciate some references. Books or Public access papers will work.
Preferably, I'd like something that gives some insight to things like the alteration of the Hamiltonian for magnetic fields among other things not covered in introductory QM course. Also, I'm interested in the numerical procedure used to actually plot the Butterfly. I'm willing to learn though, so if you post a prerequisite list, that'd work too.