Use of present perfect with just, already, yet — reference
We use the present perfect, when the action has happened recently and it is important for the present moment.
Remember these words-indicators of the present perfect:
just — a short time before
already — before we expected, (!) only in positive sentences
yet — like "already", (!) only in negatives and questions
He has just called the police.
We have already had breakfast.
Have you started the exercise yet?
My friends haven't arrived yet.