Finite gap behaviour in the superconductivity of the ‘infinite layer’ n-doped high-T_csuperconductor Sr_0.9La_0.1CuO₂

Abstract

We report on the first small-angle neutron scattering measurements from the flux line lattice (FLL) in the high-Tc cuprate superconductor Sr0.9La0.1CuO2. Using a polycrystalline sample, the scattered intensity decreases monotonically with scattering angle away from the undiffracted beam, independently of the azimuthal angle around the beam. The absence of clear peaks in the intensity suggests the establishment of a highly disordered FLL within the grains. We find that the intensity distribution may be represented by the form factor for a single flux line in the London approximation, with some contribution from crystal anisotropy. Most interestingly however, we find that, over the observed field range, the temperature dependence of the diffracted intensity is best represented by s-wave pairing, with lower limits of the gap values being very similar to the Bardeen–Cooper–Schrieffer value of Δ(0) = 1.76 kBTc. However, a qualitative consideration of corrections to the observed intensity suggests that these gap values are likely to be higher, implying strong-coupling behaviour.

Nodeless Superconducting Phase Arising from a Strong (π,π) Antiferromagnetic Phase in the Infinite-Layer Electron-DopedSr1−xHarter1, Maritato2, Shai3 et al. 2012Phys. Rev. Lett.503340View full textAdd to dashboardCite

“…On the other hand, studies of the only other known n-type family, infinite-layer A 1−x La x CuO 2 (A = Sr, Ca), suggest a less unified picture. A variety of probes including tunneling spectroscopy [4], specific heat measurements [5], neutron scattering [6], and muon spin rotation (µSR) [7] suggest a nodeless SC gap, in contrast to the holedoped cuprates and RCCO. Moreover, zero-field µSR has not reported the presence of AF order in lightly doped Sr 1−x La x CuO 2 (SLCO) [8], and its SC has been shown to be dominated by electron-like rather than hole-like carriers [9].…”

“…As argued above, the hole pocket does not possess strong coherent weight at E F and thus exhibits only a trivial temperature dependence. The gapping of the hole pocket by AF therefore can naturally explain the numerous reports of fully gapped SC in SLCO [4][5][6][7] without needing to invoke a change in the symmetry of the order parameter from d to s. This nodeless dwave scenario has been proposed theoretically by Yuan et al [27] and Das et al [28], and coexisting AF and SC has been proposed theoretically by Sénéchal et al [29]. Because the momentum range spanned by the electron pockets is narrow, we do not observe any substantial gap anisotropy, nor can we unequivocally rule out the possibility of s-wave SC.…”

Weak Superconducting Pairing and a Single Isotropic Energy Gap in Stoichiometric LiFeAs

“…Following the methodology of Ref. 31, we start with the magnetic field dependence of the low-temperature form factor that is shown in Fig. 3 (a).…”

Penetration depth of electron-doped infinite-layerSr0.88La0.12CuO2+xFruchter1, Jovanović2, Raffy3 et al. 2010Phys. Rev. B111130View full textAdd to dashboardCite

“…Concerning the issue of the order-parameter symmetry, there have been several experimental investigations for this material, most of them pointing towards a dominant s-wave superconducting order in the case of optimallydoped SLCO: the lack of a momentum dependence, as well as of a zero bias conductance peak, in tunneling spectroscopy [8]; the temperature and magnetic field scaling of the mixed state specific heat [9]; the local field distribution from low-angle neutron diffraction by the fluxline lattice [10]; the muon-spin-rotation measurements of the flux-line-lattice field distribution [6]. However, other measurements found a temperature or a magnetic field dependence indicative of nodes in the gap [11,12].…”