Abstract
Atomically uniform lead films are prepared on Si(111)-(7×7) substrates by the molecular beam epitaxy method, and their electronic structures are investigated by high-resolution angle-resolved photoemission spectroscopy and first-principles density functional theory calculations. We have observed the six-fold symmetric Fermi surfaces of Pb/Si(111)-(7×7) films. Their topology and size are almost the same regardless of the difference of film thicknesses (17, 21, 24 and 25 monolayers). The comparison between the measured and calculated thin-film Fermi surfaces suggests that the as-prepared Pb/Si(111)-(7×7) films are dominated by the hexagonal-close-packed stacking films instead of the face-centered-cubic ones. The theoretical calculations also indicate that spin–orbit coupling plays an important role in the band structures and Fermi surface topologies of Pb films.
Highlights
Our calculations indicate that the spin–orbit coupling (SOC) effect on band structure is modest along M and significant along K
Note that the calculated band structure of the hcp Pb bulk crystal shows a similar gap with the inclusion of SOC, which indicates that the features observed here are not restricted to the surface-derived states
These results highlight the importance of SOC on the band structures of Pb films, which was reported in previous studies of Pb films [17, 26]
Summary
DFT calculations show that spin–orbit coupling (SOC) plays a significant role in the band structures and FS topologies of Pb films. In figures 2(b) and (c), the calculated band structures for the 21-ML hcp Pb(0001) and fcc Pb(111) films (by including SOC) are plotted. Note that no gap was found even in hcp stacking when SOC was not included in the calculations.
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