@NikeDattani If I understand the question correctly, they are looking for a model which initially describes a system with a gap and they are interesting in looking into "band inversion", which is to do with topological insulators. Perhaps replacing the tag solid-state-physics instead? I think it is a similar tag compared to condensed-matter and both would probably too generic to narrow the question down, so replacing one would be fine?

@ProfM I was also thinking that having both solid-state-physics and condensed-matter might be a bit redundant :)

@ProfM Do you have any idea how to answer that question? It had a 100-point bounty for a week, but it expired now. I feel bad that the user wasted their bounty on it and didn't get an answer!

I don't know of an "analytical" 4-band model on top of my head. There may be one, but I imagine the user would have searched for one before asking...

@ProfM Thanks for thinking about it. It seems like the question might go unanswered for quite a while, which is also okay. We're still at only 2400 members, maybe when we reach 10,000 members then questions like this will get answered faster!