Superconductivity at 31 K in the “111”-type iron arsenide superconductor NaFeAs induced by pressureS. J. Zhang, X. C. Wang, Q. Q. Liu, Y. X. Lv, X. H. Yu, Z. J. Lin, Y. S. Zhao, L. Wang, Y. Ding, H. K. Mao and C. Q. JinEPL, 88 4 (2009) 47008DOI: https://doi.org/10.1209/0295-5075/88/47008