What is the name of the rhetoric device for the use of a one word sentence?

As you indicate, It is a rhetorical device (did you edit your title or am I going slightly mad? ;-)

In rhetoric, a rhetorical device, persuasive device, or stylistic device is a technique that an author or speaker uses to convey to the listener or reader a meaning with the goal of persuading them towards considering a topic from a perspective, using language designed to encourage or provoke an emotional display of a given perspective or action. https://en.wikipedia.org/wiki/Rhetorical_device

The ancient Greeks were very fond of these and there is a whole catalog of formally-defined ones.

At a quick glance I couldn't find the one you use but (as the saying goes) "The Greeks had a word for it". I'm sure it's in there somewhere.

P.S. Despite getting an upvote, I think I'll have to delete this answer because it doesn't fully answer the question.