Plasma frequency determination in YBa2Cu3O6+x as a function of oxygen content N. Bontemps, D. Fournier, A.C. Boccara, P. Monod, H. Alloul, J. Arabski et G. Deutscher J. Phys. France, 50 18 (1989) 2895-2901 DOI: 10.1051/jphys:0198900500180289500