2009 January 8, Y. Chassagneux, R. Colombelli, W. Maineult, S. Barbieri, H. E. Beere, D. A. Ritchie, S. P. Khanna, E. H. Linfield, A. G. Davies, “Electrically pumped photonic-crystal terahertz lasers controlled by boundary conditions”, in Nature, volume 457, number 7226