Mumford & Sons' Babel has sold 600,000 copies in its first week of release to become the biggest album debut so far this year in the U.S., according to data released Wednesday (Oct. 3) by Nielsen SoundScan. Babel, the British band's second album, will debut at the top of the Billboard 200. It surpassed first-week sales of Justin Bieber's Believe, which sold 374,000 copies immediately after its release in June. Mumford & Sons' first album, Sigh No More, has sold 2.5 million copies in the U.S. since its release in July 2010. Mumford & Sons recently traveled to Nashville to perform on CMT Crossroads with Emmylou Harris. Watch CMT Crossroads: Mumford & Sons and Emmylou Harris in its entirety.