I want to work on a research which requires both field A and field B. On the school I want to pursue, both lab X and X' from department A work on A+B. If possible, I'd like to work in both lab because there is some niches in both lab X and X' will be needed on my proposed research.
However, I would like to apply to department B because I don't want to limit myself inside a field. I want to broaden my knowledge as much as I can, before concentrating on my thesis. I don't think that this approach is bad.
Being said that, is there anything that I should be aware of when writing the SOP to department B? Would mention about the labs which aren't belonged to the department harm me in some ways? Or should I just apply to department A? Is there any harm if in my SOP there is a paragraph saying that I want to learn more about B (than A)?