Spectroscopic Evidence of Bilayer Splitting and Interlayer Pairing in an Iron Based Superconductor

Abstract

In high temperature cuprate superconductors, the interlayer coupling between the CuO${}_2$ planes plays an important role in dictating superconductivity, as indicated by the sensitive dependence of the critical temperature (T${}_C$) on the number of CuO${}_2$ planes in one structural unit. In Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$ superconductor with two CuO${}_2$ planes in one structural unit, the interaction between the two CuO${}_2$ planes gives rise to band splitting into two Fermi surface sheets (bilayer splitting) that have distinct superconducting gap. The iron based superconductors are composed of stacking of the FeAs/FeSe layers; whether the interlayer coupling can cause similar band splitting and its effect on superconductivity remain unclear. Here we report high resolution laser-based angle-resolved photoemission spectroscopy (ARPES) measurements on a newly discovered iron based superconductor, KCa${}_2$Fe${}_4$As${}_4$F${}_2$ (T${}_C$=33.5\,K) which consists of stacking FeAs blocks with two FeAs layers separated by insulating Ca${}_2$F${}_2$ blocks. Bilayer splitting effect is observed for the first time that gives rise to totally five hole-like Fermi surface sheets around the Brilliouin zone center. Band structure calculations reproduce the observed bilayer splitting by identifying interlayer interorbital interaction between the two FeAs layers within one FeAs block. All the hole-like pockets around the zone center exhibit Fermi surface-dependent and nodeless superconducting gap. The gap functions with short-range antiferromagetic fluctuations are proposed and the gap symmetry can be well understood when the interlayer pairing is considered. The particularly strong interlayer pairing is observed for one of the bands. Our observations provide key information on the interlayer coupling and interlayer pairing in understanding superconductivity in iron based superconductors.

References in corpus (29)

• Angle-resolved photoemission spectroscopy of the cuprate superconductors
• Unconventional sign-reversing superconductivity in LaFeAsO_(1-x)F_x
• Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO${}_{1-x}$F${}_x$}
• Gap symmetry and structure of Fe-based superconductors
• Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2
• Destruction of the Fermi Surface in Underdoped High Tc Superconductors
• Observation of Fermi-surface-dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2
• The superconductivity at 18 K in LiFeAs system
• LDA energy bands, low-energy Hamiltonians, t', t'', t_{perp}(k), and J_{perp}
• Effect of chemical inhomogeneity in the bismuth-based copper oxide superconductors
• Pairing Symmetry in a Two-Orbital Exchange Coupling Model of Oxypnictides
• Electronic Evidence of Temperature-Induced Lifshitz Transition and Topological Nature in ZrTe5
• Bilayer Splitting in the Electronic Structure of Heavily Overdoped Bi2Sr2CaCu2O8+d
• Importance of matrix elements in the ARPES spectra of BISCO
• Doubling of the bands in overdoped Bi2Sr2CaCu2O8-probable evidence for c-axis bilayer coupling
• Superconductivity in KCa${}_2$Fe${}_4$As${}_4$F${}_2$ with Separate Double Fe${}_2$As${}_2$ Layers
• New Developments in Laser-Based Photoemission Spectroscopy and its Scientific Applications: a Key Issues Review
• Enhancement of the superconducting gap by nesting in CaKFe4As4 - a new high temperature superconductor
• ARPES study of Pb doped Bi_2Sr_2CaCu_2O_8 - a new Fermi surface picture
• Crystal Structure and Superconductivity at about 30 K in $A$Ca${}_2$Fe${}_4$As${}_4$F${}_2$ ($A$ = Rb, Cs)
• Orbital Origin of Extremely Anisotropic Superconducting Gap in Nematic Phase of FeSe Superconductor
• Giant anisotropy in superconducting single crystals of CsCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Nodal multigap superconductivity in KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Two-gap superconductivity with line nodes in CsCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Multigap nodeless superconductivity in CsCa2Fe4As4F2 probed by heat transport
• Band-selective clean- and dirty-limit superconductivity with nodeless gaps in the bilayer iron-based superconductor CsCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Distinct Superconducting Gap on Two Bilayer-Split Fermi Surface Sheets in $B{i}_{2}S{r}_{2}CaC{u}_2{O}_{8+\delta }$ Superconductor
• Low temperature specific heat of 12442-type KCa_2Fe_4As_4F_2 single crystals
• Effect of bilayer coupling on tunneling conductance of double-layer high T_c cuprates

Cited by in corpus (17)

• Neutron spin resonance in a quasi-two-dimensional iron-based superconductor
• Friedel Oscillations of Vortex Bound States Under Extreme Quantum Limit in KCa2Fe4As4F2
• Charge Density Wave order and electron-phonon coupling in ternary superconductor Bi${}_2$Rh${}_3$Se${}_2$
• Ultrafast Optical Spectroscopy Evidence of Pseudogap and Electron-Phonon Coupling in an Iron-Based Superconductor KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Single particle tunneling spectroscopy and superconducting gaps in layered iron based superconductor KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2
• Quasi two-dimensional nature of high-Tc superconductivity in iron-based (Li,Fe)OHFeSe
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds
• Evidence of electron interaction with an unidentified bosonic mode in superconductor CsCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Second magnetization peak, anomalous field penetration, and Josephson vortices in KCa${}_2$Fe${}_4$As${}_4$F${}_2$ bilayer pnictide superconductor
• Common ($\pi$,$\pi$) Band Folding and Surface Reconstruction in FeAs-Based Superconductors
• Anomalous metallic oxygen band in the potential superconductor KCa${}_2$Fe${}_4$As${}_4$O${}_2$
• Interplay of electron-phonon coupling, pseudogap, and superconductivity in CsCa${}_2$Fe${}_4$As${}_4$F${}_2$ studied using ultrafast optical spectroscopy
• Necklace-like pattern of vortex bound states
• Multiband superconductivity and a deep gap minimum from the specific heat in KCa${}_2$(Fe${}_{1-x}$Ni${}_x$)${}_4$As${}_4$F${}_2$ ($x$ = 0, 0.05, 0.13)
• Decoupled interband pairing in a bilayer iron-based superconductor evidenced by ultrahigh-resolution ARPES