OPTICAL ANISOTROPY OF UNI2SI2

The optical anisotropy of UNi2Si2 has been systematically studied by reflectance spectroscopy in the range of 50 to 37 000 cm-1. A temperature-dependent absorption peak was found in the c-axis optical conductivity spectra centered at 280 cm-1 in the incommensurate longitudinal spin-density-wave phase (103 K < T < 130 K), which, we believe, arises from the opening up of a SDW pseudo-gap over a portion of the Fermi surface. A narrow absorption peak centered at zero frequency appears in both the c-axis and basal plane optical conductivity spectra at low temperatures. This peak results from the suppression in the scattering rate and the increase in the renormalization of the quasiparticle effective mass at low frequencies. Above the Neel temperature (T(N)), the optical conductivity decreases or saturates at low frequencies along the c-axis, while in the basal plane it develops a Drude-like absorption peak centered at omega = 0.