A paradoxical behavior of the linear polarization of luminescence has been observed in CdTe͞CdMnTe quantum wells. Although the polarization is induced by a magnetic field, neither the magnitude of the polarization nor the orientation of its plane vary when the field is rotated in the quantum well plane. An analysis shows that this can be accounted for by a low-symmetry perturbation of the crystal lattice that gives rise to a mixing of the valence subbands leading, in turn, to an anisotropy of the in-plane heavy-hole g factor. [S0031-9007(99)08866-3] PACS numbers: 78.66. Hf, 75.50.Pp, In diamond and zinc blende semiconductors, such as Si, GaAs, or CdTe, the valence-band states are fourfold degenerate at the Brillouin zone center G. The top of the valence band consists of the heavy-and light-hole subbands, each twofold degenerate in angular-momentum projection. The heavy-hole subband states are characterized by the angular momentum projections of 63͞2, and the light-hole subband states, by 61͞2.A biaxial strain usually present in quantum-well (QW) structures, as well as the difference between the light and heavy-hole effective masses result in a partial lifting of valence band degeneracy. Unless there is a strong tensile in-plane strain of the QW, the states which are higher in energy are those of the heavy-hole subband, and it is these states that determine properties of the recombination radiation emitted from QWs. The spin-orbit interaction results in a strong anisotropy of the Zeeman splitting of the hole states [1,2]. In an ideal QW having D 2d symmetry, only the longitudinal component of the heavy-hole gfactor tensor g zz is appreciable. The in-plane, or transverse components are determined by the Luttinger parameter q which describes cubic corrections to the spin Hamiltonian and which is small in value.Let us note that the transverse g factor is connected with the spin relaxation efficiency. A vanishing transverse g factor would suppress the most effective channels of the hole spin relaxation, contrary to numerous optical pumping experiments performed on low-dimensional systems which evidence a fairly high efficiency of this process [3]. Smallness of g Ќ in QWs made of diluted magnetic semiconductors, where the anisotropy of the hole exchange field gives rise to an anisotropic spin structure of the magnetic polaron state [4,5] and an unusual spin dynamics [6-9], has even more specific consequences.The present Letter reports observation of a strong dependence of the linear polarization of the photolumi-nescence in (001)-CdTe͞CdMnTe quantum wells on the direction of an in-plane magnetic field. We show that the anisotropy of the hole ground state g factor manifests itself not only as a difference between g zz and small g Ќ ; in fact, the transverse g factor is found to be also essentially anisotropic, g xx fi g yy . This anisotropy may range from moderate, jg xx j . jg yy j, to ultimately strong, g xx 2g yy , depending on the QW width and/or the barrier height. All the results can be understood assuming that th...
