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Register a new users-wave pairing in the optimally-doped LaO0.5F0.5BiS2 superconductor
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We report on the magnetic and superconducting properties of LaO0.5F0.5BiS2 by means of zero- (ZF) and transverse-field (TF) muon-spin spectroscopy measurements (uSR). Contrary to previous results on iron-based superconductors, measurements in zero field demonstrate the absence of magnetically ordered phases. TF-uSR data give access to the superfluid density, which shows a marked 2D character with a dominant s-wave temperature behavior. The field dependence of the magnetic penetration depth confirms this finding and further suggests the presence of an anisotropic superconducting gap.
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The alloys of non-centrosymmetric superconductor, Re$_3$W, which were reported to have an $alpha$-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. textbf{8}, 265 (1959)] with $T_mathrm{c}=9 $K were prepared by arc melting. The ac susceptibility and low-temperature specific heat were measured on these alloys. It is found that there are two superconducting phases coexisting in the samples with $T_mathrm{c1}sim9 $K and $T_mathrm{c2}sim7 $K, both of which have a non-centrosymmetric structure as reported previously. By analyzing the specific heat data measured in various magnetic fields, we found that the absence of the inversion symmetry does not lead to the deviation from a s-wave pairing symmetry in Re$_3$W.
The nature of the pairing state in iron-based superconductors is the subject of much debate. Here we argue that in one material, the stoichiometric iron pnictide KFe2As2, there is overwhelming evidence for a d-wave pairing state, characterized by symmetry-imposed vertical line nodes in the superconducting gap. This evidence is reviewed, with a focus on thermal conductivity and the strong impact of impurity scattering on the critical temperature Tc. We then compare KFe2As2 to Ba0.6K0.4Fe2As2, obtained by Ba substitution, where the pairing symmetry is s-wave and the Tc is ten times higher. The transition from d-wave to s-wave within the same crystal structure provides a rare opportunity to investigate the connection between band structure and pairing mechanism. We also compare KFe2As2 to the nodal iron-based superconductor LaFePO, for which the pairing symmetry is probably not d-wave, but more likely s-wave with accidental line nodes.
We have observed a Fermi-surface (FS) induced lattice modulation in a YBCO superconductor with a wavevector along CuO chains, {it i.e.} ${bf q}_1$=(0,$delta$,0). The value of $deltasim0.21$ is twice the Fermi wavevector ($2{bf k}_F$) along {bf b*} connecting nearly nested FS `ridges. The ${bf q}_1$ modulation exists only within O-vacancy-ordered islands (characterized by ${bf q}_0$=$(frac14,0,0))$ and persists well above and below $T_c$. Our results are consistent with the presence of a FS-induced charge-density wave.
Using high-energy diffraction we show that a 4-unit-cell superstructure, q0=(1/4,0,0), along the shorter Cu-Cu bonds coexists with superconductivity in optimally doped YBCO. A complex set of anisotropic atomic displacements on neighboring CuO chain planes, BaO planes, and CuO2 planes, respectively, correlated over ~3-6 unit cells gives rise to diffuse superlattice peaks. Our observations are consistent with the presence of Ortho-IV nanodomains containing these displacements.
The spin dynamics of an optimally doped YBa2Cu3O7 (Tc = 93 K) crystal array have been investigated in a wide range of momentum and energy (Q - E) space using the time-of-flight neutron scattering method. Incommensurate spin modulation in Q is a characteristic feature, as it is in the under-doped YBa2Cu3O6.7 with a different incommensurability. A linear relationship between the incommensurability and Tc is proposed. Along with the discovery of the same incommensurability in under-doped La2-ySryCuO4, it may be a generic characteristic of the high-Tc oxide superconductor.
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