I think the most fundamental belief behind that worldview, is that most fundamental theoretical entities of physics (whatever they may turn out to be–particles, waves, strings, branes, forces, fields, etc) are the only ultimate reality, and everything else which exists somehow bases its existence on them. The non-existence of God is merely a consequence of that fundamental belief, not a fundamental belief in itself. "Naturalism", "materialism", "physicalism" all do a better job of naming that fundamental belief than "atheism" does, which is a word which refers to a non-fundamental consequence of it.

"Antisupernaturalism" is another option, albeit it has the disadvantage of being purely negative, whereas I think this worldview actually makes positive claims about the nature of reality and how it can be known.