Three Dimensionality and Orbital Characters of the Fermi Surface in(Tl,Rb)yFe2−xSe2

Abstract

We report a comprehensive angle-resolved photoemission spectroscopy study of the tridimensional electronic bands in the recently discovered Fe selenide superconductor ðTl; RbÞ y Fe 2Àx Se 2 (T c ¼ 32 K). We determined the orbital characters and the k z dependence of the low energy electronic structure by tuning the polarization and the energy of the incident photons. We observed a small 3D electron Fermi surface pocket near the Brillouin zone center and a 2D like electron Fermi surface pocket near the zone boundary. The photon energy dependence, the polarization analysis and the local-density approximation calculations suggest a significant contribution from the Se 4p z and Fe 3d xy orbitals to the small electron pocket. We argue that the emergence of Se 4p z states might be the cause of the different magnetic properties between Fe chalcogenides and Fe pnictides.

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

“…Experimentally, the κ band is found to be mainly made of d z 2 with just a trace of d xz /d yz , while it is dominated by d xz /d yz in the calculations. A previous ARPES study suggests that the κ band is the mixture of the Se 4p and Fe 3d orbitals [35]. Although our calculations show a minimal involvement of the Se 4p orbitals, our polarization-dependent study cannot distinguish the Se 4p z from the Fe 3d z 2 orbitals, thus we leave this issue open.…”

Spectromicroscopy of electronic phase separation in KxFe2−ySe2 superconductor

“…1c and 1d respectively. Despite limited energy and momentum resolutions (~50 meV and 0.05  Å −1 ), the energy dispersive structures in the bright regions of SPEM looks similar to the band structure measured by space integrated ARPES1920212223. On the other hand, no dispersing structures are seen close to E F in the dark region, neither around Γ (zone center) nor around M (zone corner), suggesting the dark region being due to an insulating/semiconducting phase.…”

“…Following earlier high resolution space integrated ARPES, the spectral weight around the zone center (Γ-point) can be assigned to weak electron-like band κ crossing E F . This weak band is known to be mainly due to the Fe 3 d xy orbitals with admixed Se 4 p z orbitals2223. At slightly higher binding energies, around 80 meV below E F , spectral weight due to α and β bands with hole-like character can be seen.…”

Orbital-selective pairing and superconductivity in iron selenides

“…50 This is important for the consideration of the quasiparticle excitation gap at the small electron pocket of K y Fe 2−x Se 2 near the origin of the BZ. According to the ARPES experiments, 52,53 this Fermi pocket contains Fe 3d xy and Se 4p z orbitals (α band), while the hole (β) bands containing both 3d xz and 3d yz orbitals are only~60-80 meV below the Fermi energy. We therefore expect that both the intraband and interband pairing components will be significant for this part of the BZ and the mechanism advanced here will make the quasiparticle excitations to be fully gapped for this small electron pocket.…”