Electron-phonon coupling and temperature-dependent shift of surface states on Be(1010)

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The temperature dependence of two Schockley surface states (S1 and S2) on Be(1010), located in a wide bulk projected hand gap from A to Γ, has been investigated with angle-resolved photoemission spectroscopy. The electron-phonon coupling of the surface states S1 and S2 at the zone boundary (A) were determined using both Debye and Einstein phonon models. Based on fitting, this analysis indicates that the surface optical phonon mode located around 64 meV contributes most strongly to the electron-phonon coupling of the S1 surface state, which is highly localized in the surface layer. The determined electron-phonon coupling parameter λ of S1 and S2 (0.647 and 0.491, respectively) is distinct from the bulk value (λbulk=0.24). Both surface states S1 and S2 are observed to shift linearly with the temperature, but in opposite directions at the rates of (-0.61±0.3) × 104 eV/K and (1.71±0.8) × 10-4 eV/K, respectively. The different behavior of the two surface states, with respect to both the electronic-phonon coupling and temperature-dependent shift of initial energy, is attributed to the higher surface charge localization of S1 than S2.

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Physical Review B - Condensed Matter and Materials Physics

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