Man, I always get a bit wary when I see requests for this dynamic because it's so easy for things to get creepy or just plain poorly written. For mature readers, I'd steer you toward books that use the power imbalance as a framework for something deeper, not just as cheap taboo fuel. A classic like Donna Tartt's 'The Secret History' fits this. The professor-student relationship there is all about intellectual seduction and the dangerous allure of a charismatic teacher leading his students into a morally gray world. It's less about romance and more about obsession, philosophy, and the corruption of innocence.
If you're looking for something with a romantic element but handled with more nuance, 'The Love Hypothesis' by Ali Hazelwood comes to mind, though it's more of a post-grad researcher and professor scenario. It's a lot lighter and sweeter, playing with tropes but in a consensual, adult framework. For a darker, gothic take, Diane Setterfield's 'The Thirteenth Tale' has elements of a biographer uncovering a writer's past, which creates a kind of investigative student-teacher dynamic, full of secrets and revelations. Maturity here is in the unraveling of a complex psychological puzzle, not in the relationship itself.