List Posts By A Co-Author Not Working

So, I hacked the method to obtain the user slug by capturing the URI.

$slug = $_SERVER['REQUEST_URI'];
$slug = str_replace('author', '', $slug);
$slug = str_replace('/', '', $slug);

I plugged this into the $args variable for the wp query.

$args = array(
    'post_type' => 'posts',
    'posts_per_page' => 10,
    'post_status' => 'publish',
    'tax_query' => array(
        array(
            'taxonomy' => 'author',
            'field' => 'slug',
	    'terms' => $slug,
        ),
    ),
);