Surface electronic structures of ferromagnetic Ni(111) studied by STM and angle-resolved photoemission

Spin-polarized surface electronic states in Ni(111) have been examined using scanning tunneling microscopy (STM) and spectroscopy (STS) combined with high-resolution angle-resolved photoemission spectroscopy (HR-ARPES). Standing waves derived from the majority-spin Shockley surface state (SS) have been observed in the STM and dI/dV images. The fast Fourier transform (FFT)-dI/dV image at a different sample bias exhibited a circular contour in the reciprocal space. The radius of the FFT-dI/dV image was in agreement with that of the corresponding constant-energy contour given by the HR-ARPES. The majority-spin Shockley SS is partially occupied and disperses upward, crossing the Fermi level (EF) at a wave number of k(F) = 0.081 +/- 0.005 angstrom(-1). The effective mass (m*) with respect to the free-electron mass (me) of the majority-spin Shockley SS was evaluated to be m*/m(e)=0.19 +/- 0.03. The STS spectrum indicated a pair of the Shockley SS below and above EF with an exchange splitting of similar to 190 meV. By the line-shape analyses of the HR-ARPES spectrum, the lifetime broadening at the (Gamma) over bar point was calculated to be 53.6 meV, which agrees well with the width (49 meV) of the steplike structure in the STS spectrum. The results from the STM/STS and HR-ARPES experiments were found to be mutually consistent.