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

Abstract

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 $(\text{FFT})\text{\ensuremath{-}}dI/dV$ image at a different sample bias exhibited a circular contour in the reciprocal space. The radius of the $\text{FFT-}dI/dV$ 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 $({E}_{F})$ at a wave number of ${k}_{F}=0.081\ifmmode\pm\else\textpm\fi{}0.005\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$. The effective mass $({m}^{\ensuremath{\ast}})$ with respect to the free-electron mass $({m}_{e})$ of the majority-spin Shockley SS was evaluated to be ${m}^{\ensuremath{\ast}}/{m}_{e}=0.19\ifmmode\pm\else\textpm\fi{}0.03$. The STS spectrum indicated a pair of the Shockley SS below and above ${E}_{F}$ with an exchange splitting of $\ensuremath{\sim}190\text{ }\text{meV}$. By the line-shape analyses of the HR-ARPES spectrum, the lifetime broadening at the $\overline{\ensuremath{\Gamma}}$ 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.