Does it violate academic social norm to email someone around midnight? I do this often because this is when I wrap up the stuff for my day. But I wonder if it is considered intrusive. 

I imagine a scenario where a phone that is linked to gmail rings due to my email, and that wakes up the person I intend to email.

Can people chime in whether it is out of the norm to email around midnight? 

Should I try to refrain from doing this?
The good thing (maybe the only good thing) about email is that it's by nature asynchronous. A phone call in the middle of the night is intrusive, because there is an explicit expectation that the receiver does something about the call right there and then. An email is not like that - if you send an email, it will happily sit in the inbox of the recipient until they explicitly take an action to react upon it. Consequently, it does not matter when you send the email.


  I imagine a scenario where a phone that is linked to gmail rings due to my email, and that wakes up the person I intend to email.


This is, in my opinion, not a valid concern. First of all, the kind of person who is annoyed by getting disturbed by email outside of work hours has a very easy fix to the problem - turn off notifications. In my opinion, if you explicitly have notifications enabled you can't at the same time be annoyed that you get notified. 

Second, you'll need to understand an almost universal basic truth - starting from a certain seniority, most people in academia get a lot of email. Hundreds per day, in some cases. Many of these emails will come in during the night. If you wake up every time you get an email from one of your collaborators on a different continent, you won't get much sleep at all. So your email is highly unlikely to wake anybody up, because it will drown in the flood of other emails people get over the night.

That said, as discussed in a somewhat related recent question, if you are a supervisor or manager, it may pay to be somewhat careful about what "message" you transport with when you send emails. In this question, a student was stressed because their supervisor kept sending them mails in the night, and the student interpreted these as work items that needed to be done by the next morning. Also, if you as a supervisor are clearly working until midnight, it may implicitly communicate certain expectations and standards that you don't really want in your team.