Authors: L A Ponomarenko; R V Gorbachev; G L Yu; D C Elias; R Jalil; A A Patel; A Mishchenko; A S Mayorov; C R Woods; J R Wallbank; M Mucha-Kruczynski; B A Piot; M Potemski; I V Grigorieva; K S Novoselov; F Guinea; V I Fal'ko; A K Geim Journal: Nature Date: 2013-05-15 Impact factor: 49.962