ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism

Abstract

Its direct momentum sensitivity confers to angle-resolved photoemission spectroscopy (ARPES) a unique perspective in investigating the superconducting gap of multi-band systems. In this review we discuss ARPES studies on the superconducting gap of high-temperature Fe-based superconductors. We show that while Fermi-surface-driven pairing mechanisms fail to provide a universal scheme for the Fe-based superconductors, theoretical approaches based on short-range interactions lead to a more robust and universal description of superconductivity in these materials. Our findings are also discussed in the broader context of unconventional superconductivity.

Is BaCr2As2 symmetrical to BaFe2As2Richard1, Roekeghem2, Lv3 et al. 2017Phys. Rev. B193120View full textAdd to dashboardCite

“…The antiferromagnetic wave vector in the Fe-based superconductors connects hole and electron pockets FS pockets, giving rise to the quasi-nesting scenario suggesting that low-energy spin fluctuations may contribute to the superconducting pairing [28][29][30]. Although the quasi-nesting scenario is now seriously challenged [19], in particular due to the existence of high-T c superconductivity without hole FS pocket in A x Fe 2−x Se 2 [31][32][33][34] and FeSe monolayers [35][36][37][38][39], the Γ-M wave vectors connects the top of the holelike bands and the bottom of the electron bands within an energy range smaller than a few hundreds of meV in all Febased superconductors, suggesting that high-energy spin fluctuations (local moments) may play a role. There is no such electron-hole connection with the antiferromagnetic wave vector in BaCr 2 As 2 .…”

Role of the orbital degree of freedom in iron-based superconductors

“…72,73 ARPES studies on Ba 1−x K x Fe 2 As 2 and LiFeAs show that the superconducting gap on the d xz /d yz hole pockets is much larger than that on the d xy hole pocket. 62 All these results seem to suggest the dominating role of intra-orbital pairing in FeSCs.…”

“…This, too, seems to vary between different compounds. For most iron-pnictide compounds studied with comparable hole and electron pockets, the d xz /d yz hole pockets show larger superconducting gap than the d xy hole pocket, 62,74 suggesting the importance of d xz /d yz orbitals to superconductivity. Consistently, in LiFe 1−x Co x As and Ba(Fe 1 −x Co x ) 2 As 2 , when the d xz /d yz hole pockets vanish with electron doping, superconductivity is strongly suppressed.…”

Enhancement of the Superconducting Gap by Nesting inCaKFe4As4: A New High Temperature Superconductor

“…The superconducting mechanism in iron-based, high temperature superconductors is an important topic in condensed matter physics. One key question is whether the system should be described within a weak coupling BCS-type approach with a key role played by the interband repulsion between electron and hole bands, separated by the large momentum transfer or by a strong coupling approach with dominant short-range antiferromagetic (AF) fluctuations, described by the local exchange interaction [1][2][3][4][5][6][7]. The former scenario seemed consistent with experimental results from a number of iron pnictide superconductors [8], but was later challenged by the discovery of iron chalcogenide-based superconductors [9,10].…”