THEORY OF CIRCULAR-DICHROISM IN PHOTON STM EXPERIMENTS ON MAGNETIC SAMPLES

Recent experiments on the circular dichroism using a photon emission s canning tunneling microscope (PSTM) on magnetic samples are analyzed b y a theoretical approach that includes the influence of the sample-tip geometry and the anisotropic response of the ferromagnetic substrate. We obtain an expression for the degree of circular polarization in th e emitted light that leads to a reasonable agreement with the experime ntal data. Combining our theoretical analysis with measurements of the circular dichroism using PSTM offers a convenient way to determine lo cally the optical constants of a magnetic