Magnetic field effects on exciton and biexciton states in CuBr

In CuBr the polariton dispersion E(→Q,→H) in the presence of a magnetic field →H is dissymmetric with respect to →Q and →H, →Q denoting the polariton wave vector. We study this dissymmetry using hyper-Raman scattering techniques in the presence of a static magnetic field which is varied between - 70 and 70 kG in a given configuration. The experimental results are quantitatively explained, considering →Q and →H-linear terms in the exciton Hamiltonian. The effective g values and the CQ-linear interaction term are determined with a good accuracy and an upper limit of the anisotropic exciton-mass parameters is established. Since biexcitons are involved in the scattering process, the influence of the magnetic field on their different states and on the selection rules of hyper-Raman scattering are studied. In agreement with our theoretical considerations, no decomposition of the biexciton ground state has been observed.