Optically induced coherent transport far above Tc in underdoped YBa 2 Cu 3 O 6 + δ

S. Kaiser,1,* C. R. Hunt,1,4 D. Nicoletti,1 W. Hu,1 I. Gierz,1 H. Y. Liu,1 M. Le Tacon,2 T. Loew,2 D. Haug,2 B. Keimer,2 and A. Cavalleri1,3,† 1Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany 2Max Planck Institute for Solid State Research, Stuttgart, Germany 3Department of Physics, Oxford University, Clarendon Laboratory, Oxford, United Kingdom 4Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA (Received 18 March 2014; revised manuscript received 25 April 2014; published 30 May 2014)