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

摘要

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 dl/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 (E_F) at a wave number of k_F =0.081 ±0.005 A~(-1). The effective mass (m~*) with respect to the free-electron mass (m_e) 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 E_F with an exchange splitting of ～190 meV. By the line-shape analyses of the HR-ARPES spectrum, the lifetime broadening at the Γ 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.