Surface and bulk electronic structures of LaFeAsO studied by angle-resolved photoemission spectroscopy

Abstract

The electronic structure of LaFeAsO, a parent compound of iron-arsenic superconductors, is studied by angle-resolved photoemission spectroscopy. By examining its dependence on photon energy, polarization, and sodium dosing, both the bulk and the surface contributions are identified. We find that a bulk band moves toward high binding energies below the structural transition temperature, and shifts smoothly across the spin-density-wave transition by about 25 meV. Our data suggest that the band reconstruction may play a crucial role in the spin-density-wave and the structural transitions. For the surface states, both the LaO-terminated and FeAs-terminated components are revealed. Certain small band shifts are observed for the FeAs-terminated surface states in the spin-density-wave state, which might be a reflection of the bulk electronic-structure reconstruction. Moreover, sharp quasiparticle peaks quickly rise at low temperatures, indicating drastic reduction in the scattering rate. A kink structure in one of the surface band is shown to be possibly related to the enhanced electron-phonon interactions on the polar surface.

The orbital characters of low-energy electronic structure in iron-chalcogenide superconductor K x Fe2−y Se2

“…Based on Table 1, these two bands are made of the d z 2 and/or d xz orbitals. The ω and ω bands in other iron-based superconductors were found to be made of d z 2 by both experiments and band calculations [13,23], thus here we could attribute them to the d z 2 orbitals as well. However, since the d z 2 orbital is mixed with the d xz orbital in the κ band, there should be a finite mixing of the d xz orbital in these two bands.…”

“…The insulating parental phase even exhibits certain Mott-insulator signatures, and it is phase separated from the superconducting phase in the K x Fe 2−y Se 2 superconductor at a mesoscopic scale [7,10]. Moreover, angle-resolved photoemission spectroscopy (ARPES) studies have shown that its Fermi surface is consisted of electron pockets only [7,11,12], which is again distinct from most of the iron-based superconductors [13][14][15][16][17]. These unique properties of K x Fe 2−y Se 2 have raised a lot of interest.…”

“…Polarization-dependent ARPES experiments have been conducted extensively on the iron-based superconductors, including LaOFeAs [13], BaFe 2 As 2 [23][24][25][26][27], NaFeAs [28,29], and FeTe [17,27]. Here we report the polarization-dependent ARPES study on the orbital characters of K x Fe 2−y Se 2 superconductor.…”

S4Symmetric Microscopic Model for Iron-Based Superconductors

“…The above model is capable of quantitatively describing the experimental results measured by ARPES [14,20,[41][42][43][44]. Although the hopping parameters are dominated by t 1s , t 2d , and t 2s , other parameters cannot be ignored.…”

Quasiparticle Interference ofC2-Symmetric Surface States in a LaOFeAs Parent Compound

“…Density functional theory (DFT) calculations also suggest the formation of 2D surface states on the highly polar surfaces of cleaved LaOFeAs, with electronlike surface band on LaO and holelike surface band on FeAs [33]. Recent ARPES data provide direct evidence for the existence of surface states by showing the lack of k z dispersion for certain bands on cleaved LaOFeAs [34,35].…”