@NikeDattani interesting points, but not sure I have a good answer. I do think topological-insulators is too narrow, and looking at some of the most recent questions with this tag, it is being used for topological insulators (as one would expect) but also for topological semimetals, Chern insulators, etc. Something like topological-condensed-matter would include all of these instances, but then it would perhaps be too broad?

I am not sure if there are yet any questions on this topic, but there is a lot of research interest recently on topological phonons, topological metamaterials, etc. All of these would be included in something like topological-condensed-matter, but again perhaps too broad?

@ProfM Thanks so much for the valuable feedback here! topological-insulators has only 23 questions, and combined with topological-analysis we have only 26 questions in total. This would make the combined "topological" tag, to become the 35th most popular tag on the site. If we don't combine them, then they'll appear even further down in our list of tags, so I don't mind combining them.

Even if we made it more broad to include everything "topological" in matter modeling, I wouldn't mind because it would still be a relatively small tag. The condensed-matter tag only has 54 questions and is our 16th most popular tag (it's relatively small compared to dft, molecular-dynamics, vasp, etc. which have 100-400 questions each!), so a tag covering everything "topological" in condensed-matter would still be relatively small, no matter how broad it gets.

Okay, after more careful analysis, 2 of the questions from the topological-analysis tag were not actually about "topological matter", they seem to have been more related to this technique from applied mathematics called topological data analysis which uses techniques from topology to analyze data.

This use of the word "topology" was also not so much related to "topological matter":

So topological-analysis has been effectively burninated now, and we can broaden topological-insulators to topological-matter in order to include things like semi-metals. People only interested in insulators may find this to be too broad, so we can also have an insulators tag.

The combination of [topological-matter] and [insulators] would allow questions about topological-insulators to be seen by the entire community of people interested in topological-matter, and the entire community of people interested in insulators. Otherwise, [topologial-insulators] seems to be too narrow (only 23 questions).