What is the rarest material known to man?

Can you elaborate on what the rarest material known to mankind might be? Is it a naturally occurring element, or is it something that's been artificially created? What sets this material apart from others in terms of its scarcity, and what potential applications or uses does it have in the fields of science, technology, or industry? Additionally, how has the discovery or synthesis of this material impacted our understanding of the natural world or advanced our technological capabilities?