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Register a new userA 4-unit-cell superstructure in optimally doped YBa2Cu3O6.92 superconductor
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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.
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We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd$_{1.85}$Ce$_{0.15}$CuO$_{4-delta}$ above and below its superconducting transition temperature $T_c=25$ K. In addition to gradually opening a spin pseudo gap at the antiferromagnetic ordering wavevector ${bf Q}=(1/2,1/2,0)$, the effect of superconductivity is to form a resonance centered also at ${bf Q}=(1/2,1/2,0)$ but at energies above the spin pseudo gap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-$T_c$ superconductivity.
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.
Polarized-neutron diffraction experiments (PND) have revealed that the pseudogap state of the cuprates exhibits unusual intra-unit-cell (IUC) magnetism. At a qualitative level, the data indicate a moment direction that is neither perpendicular nor parallel to the CuO2 layers, yet an accurate measurement of a structurally simple compound has been lacking. Here we report PND results with unprecedented accuracy for the IUC magnetic order in the simple-tetragonal single-CuO$_2$-layer compound HgBa2CuO$_{4+{delta}}$. At the transition temperature, we find evidence for magnetic critical scattering. Deep in the ordered state, we determine the moment direction to be 70{deg} $pm$ 10{deg} away from the normal to the CuO$_2$ layers, which rules out both purely planar loop currents and high-symmetry Dirac multipoles, the two most prominent theoretical proposals for the microscopic origin of the IUC magnetism. However, the data are consistent with Dirac multipoles of lower symmetry or, alternatively, with a particular configuration of loop currents that flow on the faces of the CuO$_6$ octahedra.
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.
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