Mumford & Sons' 'Babel' No. 1 with year's biggest debut sales week

There's no sign of a sophomore slump for rock group Mumford & Sons.

With their second album, "Babel," they've notched their first No. 1 album on the Billboard 200 chart, as well as the first No. 1 album for their record label, Glassnote Records.

And with 600,000 copies of "Babel" sold in the first week following its September 25 release, Mumford & Sons has the biggest debut sales week of the year.

The rockers even overcame Bieber fever, setting a new benchmark after pop star Justin Bieber's "Believe" sold 374,000 copies in its debut week in June. Until now, that album had the biggest debut sales week of the year, followed by Madonna's "MDNA" (359,000 sold) and Pink's "The Truth About Love," which, with 280,000 sold, also earned that artist her first No. 1.

But Mumford & Sons can't claim the largest overall sales week in 2012 - that title goes to Adele and her indomitable "21."