Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors

Abstract

Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors.

Fermiology of 122 family of Fe-based superconductors: An ab initio study

“…SDW order (or orbital order) is controlled by inter-band nesting of FSs which in turn is related to the dimensionality of the FSs. Emergence of superconductivity in these Fe-based systems seem to be originated from spin fluctuation or orbital fluctuation which may be enhanced by quasi-nesting of two-dimensional electron and hole FSs as suggested by M. Sunagawa et al [28]. Since the FSs are Fe-d orbital derived, Co-doping (which has one more d-electron than Fe) clearly causes disturbance and makes modification to the electronic and hole FSs.…”

Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides

“…Another achievement is the simultaneous La and P doping of CaFe 2 As 2 [23]: melt-grown crystals of (Ca 1– x La x )Fe 2 (As 1– y P y ) 2 exhibited bulk superconductivity with a maximum T c of 45 K for 0.12 ≤ x ≤ 0.18 with y = 0.06, while (Ca 1– x La x )Fe 2 As 2 without phosphorus exhibited filamentary superconductivity [23]. Characteristic two-dimensional Fermi surfaces were observed by means of angle-resolved photoemission spectroscopy (ARPES) in the 45 K phase of La- and P-doped CaFe 2 As 2 [212]. …”

“…Angle-resolved photoemission spectroscopy (ARPES) [212] revealed that (Ca 0.82 La 0.18 )Fe 2 (As 0.94 P 0.06 ) 2 with T c = 45 K possesses only cylindrical hole- and electron-like Fermi surfaces (FS). The size of the β hole-like FS is nearly the same as that of the ε electron-like FS, and both FS have a weak k z dispersion, thus giving rise to a quasi-nesting.…”

“…This feature is similar to that for directly electron-doped Ba(Fe 1– x Co x ) 2 As 2 ( T c = 23 K). Sunagawa et al [212] pointed out that a noticeable difference between (Ca 0.82 La 0.18 )Fe 2 (As 0.94 P 0.06 ) 2 and Ba(Fe 1– x Co x ) 2 As 2 is the dimensionality of the inner hole-like FS; the inner hole-like FS ( α 2 ) of the former shows a cylindrical shape, while that of the latter shows a strong k z dispersion and is closed near the Γ point. It has been suggested that the tendency toward quasi-nesting between α 2 and β , together with β and ε, can induce high T c in (Ca 0.82 La 0.18 )Fe 2 (As 0.94 P 0.06 ) 2 [212].…”

Origin of structural and magnetic transitions in BaFe$_{2-x}$RuxAs2materials

“…1 (j) and follow below). Such non-degenerate d xz , d yz bands are observed experimentally recently [32]. We define orbital order as, < O >= i=Γ,X E dxz (i) -E dyz (i) which are presented as a function of temperature in the first two figures of the bottom row of Fig.…”