# Corner symbol directly over a letter

I'd like to know how to add a corner symbol directly above a letter in math-mode, such as in the following image:

I have tried the commands \urcorner or \ulcorner from the amssymb package and they are not what I need.

\documentclass{article}
$\mathfrak{L}(x) =\partial^\mu \URcorner\lambda(x)...\URcorner x$