The most common and most likely answer to this crossword clue is the 7 letter word COULOMB
I've seen this crossword clue in Independent
C
O
U
L
O
M
B
Buddy explains!

The straight part
We know that "physicist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case physicist = coulomb.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COULOMB mean?
COULOMB noun- In the International System of Units, the derived unit of electric charge; the amount of electric charge carried by a current of 1 ampere flowing for 1 second. Symbol: C