[lambdatronics]

In my field (experimental plasma physics) the general convention is that the PI's name goes last on the paper, while the first author is the one who did the bulk of the work and wrote the manuscript, with the other coauthors usually playing small supporting roles.

This field also tends to have very large grants (~$10-100mn/yr) that support dozens of researchers, because of the large centralized facilities, so it's easier for students to have some self-direction.