@article{GrueningervanderMarelDamascellietal.2000,
  author    = {Markus Gr{\"u}ninger and D. van der Marel and A. Damascelli and A. Erb and Tamara Nunner and Thilo Kopp},
  title     = {Midinfrared absorption in YBa2Cu3O6: Evidence for a failure of spin-wave theory for spin 1/2 in two dimensions},
  journal   = {Physical Review B},
  volume    = {62},
  number    = {18},
  pages     = {12422 -- 12426},
  doi       = {10.1103/physrevb.62.12422},
  year      = {2000},
}