Enter your email address and we send you a six-digit code. Type it in and you are signed in — you stay on the same page and keep whatever you had typed. The code is good for ten minutes and for five attempts.
A code rather than a link you go away and click, because a link lands you in your mail client and back on a fresh page with whatever you had typed gone. Staying put is the whole point.
There is no password because a password on a research tool is one more thing to leak and one more thing to reset. We store only a hash of each code and each session, never anything reusable.