Surface electronic structure of NiMnSb(001)

We report on surface band structure measurements for the (001) surface of single crystal NiMnSb by angle-resolved photoelectron spectroscopy. Through comparisons of our data with previous angle-integrated experiments on various samples, polycrystals, and single crystals, we show that the binding energies of the observed photoemission peaks are sensitive to the particular surface condition and/or preparation. Additionally, our $\mathbf{k}$-resolved measurements reveal a clear energy dispersion of the observed spectral features and a surface state candidate. We compare our measurements to fully-relativistic theoretical calculations and find that while they do not agree with the experimentally observed band dispersion they do explain the elemental origin and energy position of the normal emission photoemission results.

Figure 1

Crystal lattice of NiMnSb. The black circles represent Mn, the dark gray Sb, and the light gray Ni atoms. Note the empty positions within the Ni planes.

Figure 2

LEED pattern of a clean NiMnSb(001) surface taken with $44\mathrm{eV}$ electrons.

Figure 3

Auger scan ($1.8\mathrm{keV}$ primary electron energy) of a clean NiMnSb(001) surface.

Figure 4

Normal-emission UPS data for NiMnSb(001). The lower spectrum was obtained from a sputtered surface (without annealing), the upper spectrum from a sputtered and annealed surface (at $400°\mathrm{C}$). The peaks marked $B_1$ and $B_2$ are due to direct transitions from hybridized Ni-Mn $d$-states. $B_1$ occurs at $1.3\mathrm{eV}$ $\left(0.9\mathrm{eV}\right)$ binding energy for the annealed (sputtered) surface while $B_2$ appears only in the spectrum from the annealed surface at $3.1\mathrm{eV}$ binding energy.

Figure 5

Calculated spin polarized bulk band structure of NiMnSb along $\Gamma X$. Bulk states are shown in gray and possible final states are shown as dashed black lines. The latter have been shifted by $21.2\mathrm{eV}$, our photon energy, to identify possible direct transitions as intersections between these lines (circled). The different symbols denote the different elements from which the bands are derived.

Figure 6

Angle-resolved UPS data from the NiMnSb(001) surface Brillouin zone in the $\overline{\Gamma }\overline{\mathrm{X}}$ direction. The bold lines are a guide to the eye for the peak dispersion.

Figure 7

Same as Fig. 6 but for the $\overline{\Gamma }\overline{\mathrm{M}}$ direction.

Figure 8

Calculated and measured UPS spectra for normal emission and 10° off normal emission from the NiMnSb(001) surface. The data are plotted as lines with points and the calculations as lines. The 0° data and theory are black and the 10° data and theory are gray.

Figure 9

Experimental $E$ versus ${\mathbf{k}}_{\Vert }$ dispersion curves and calculated projected bulk band structure. The data are black circles and the shaded regions of dark (spin down), light (spin up), and neutral (both spin up and spin down) gray are based on calculations.