Dynamics of anisotropic spin dimer system in strong magnetic field
  Recently measured high-field ESR spectra of the spin dimer material TlCuCl3 are described within the framework of an effective field theory. A good agreement between the theory and experiment is achieved, for all geometries and in a wide field range, under the assumption of a weak anisotropy of the interdimer as well as intradimer exchange interaction. 
A. K. Kolezhuk, V. N. Glazkov, H. Tanaka, and A. Oosawa