2D orbital-like magnetic order in La2−xSrxCuO4{\rm La_{2-x}Sr_xCuO_4}

In high temperature copper oxides superconductors, a novel magnetic order associated with the pseudogap phase has been identified in two different cuprate families over a wide region of temperature and doping. We here report the observation below 120 K of a similar magnetic ordering in the archetypal cuprate ${\rm La_{2-x}Sr_xCuO_4}$ (LSCO) system for x=0.085. In contrast to the previous reports, the magnetic ordering in LSCO is {\it\bf only} short range with an in-plane correlation length of $\sim$ 10 \AA\ and is bidimensional (2D). Such a less pronounced order suggests an interaction with other electronic instabilities. In particular, LSCO also exhibits a strong tendency towards stripes ordering at the expense of the superconducting state.Comment: 4 figures, submitted to Phys. Rev. Let

Tuning the superconducting and magnetic properties in Fe_ySe_0.25Te_0.75 by varying the Fe-content

The superconducting and magnetic properties of Fe$_{y}$Se$_{0.25}$Te$_{0.75}$ single crystals ($0.9\leq y \leq1.1$) were studied by means of x-ray diffraction, SQUID magnetometry, muon spin rotation, and elastic neutron diffraction. The samples with $y<1$ exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for $y\geq 1$, but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the Fe$_{y}$Se$_{1-x}$Te$_{x}$ can be tuned not only by varying the Se/Te ratio but also by changing the Fe content

Spin anisotropy of the resonance in superconducting FeSe0.5Te0.5

We have used polarized-neutron inelastic scattering to resolve the spin fluctuations in superconducting FeSe0.5Te0.5 into components parallel and perpendicular to the layers. A spin resonance at an energy of 6.5 meV is observed to develop below T_c in both fluctuation components. The resonance peak is anisotropic, with the in-plane component slightly larger than the out-of-plane component. Away from the resonance peak the magnetic fluctuations are isotropic in the energy range studied. The results are consistent with a dominant singlet pairing state with s^{\pm} symmetry, with a possible minority component of different symmetry.Comment: 5 pages, 4 figure

Momentum-Resolved Electronic Structure of the High-TcT_{c} Superconductor Parent Compound BaBiO3_{3}

We investigate the band structure of BaBiO$_{3}$, an insulating parent compound of doped high-$T_{c}$ superconductors, using \emph{in situ} angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO$_{6}$ breathing distortions. Though the distortions are often thought to coincide with Bi$^{3+}$/Bi$^{5+}$ charge ordering, core level spectra show that bismuth is monovalent. We further demonstrate that the bands closest to the Fermi level are primarily oxygen derived, while the bismuth $6s$ states mostly contribute to dispersive bands at deeper binding energy. The results support a model of Bi-O charge transfer in which hole pairs are localized on combinations of the O $2p$ orbitals.Comment: minor changes to text and other figures; includes link to online Supplemental Material; accepted to Phys. Rev. Let

Exotic Kondo crossover in a wide temperature region in the topological Kondo insulator SmB6 revealed by high-resolution ARPES

Temperature dependence of the electronic structure of SmB6 is studied by high-resolution ARPES down to 1 K. We demonstrate that there is no essential difference for the dispersions of the surface states below and above the resistivity saturating anomaly (~ 3.5 K). Quantitative analyses of the surface states indicate that the quasi-particle scattering rate increases linearly as a function of temperature and binding energy, which differs from Fermi-Liquid behavior. Most intriguingly, we observe that the hybridization between the d and f states builds gradually over a wide temperature region (30 K < T < 110 K). The surface states appear when the hybridization starts to develop. Our detailed temperature-dependence results give a complete interpretation of the exotic resistivity result of SmB6, as well as the discrepancies among experimental results concerning the temperature regions in which the topological surface states emerge and the Kondo gap opens, and give new insights into the exotic Kondo crossover and its relationship with the topological surface states in the topological Kondo insulator SmB6.Comment: 8 pages, 5 figure

Magnetic excitations of Fe_{1+y}Se_xTe_{1-x} in magnetic and superconductive phases

We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe1.01Se0.50Te0.50 and non-superconducting Fe1.10Se0.25Te0.75. We confirm the existence of a spin resonance in the superconducting phase of Fe1.01Se0.50Te0.50, at an energy of 7 meV and a wavevector of (1/2,1/2,0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2,1/2,0)\pm(0.18,-0.18,0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low-energy magnetic excitation is also observed in Fe1.10Se0.25Te0.75 close to the commensurate antiferromagnetic ordering wavevector (1/2-\delta,0,1/2) where \delta \approx 0.03. The magnetic correlations in both samples are found to be quasi-two dimensional in character and persist well above the magnetic (Fe1.10Se0.25Te0.75) and superconducting (Fe1.01Se0.50Te0.50) transition temperatures.Comment: 10 pages, 4 figure

Coexistence of incommensurate magnetism and superconductivity in Fe_{1+y}Se_xTe_{1-x}

We report an investigation into the superconducting and magnetic properties of Fe_{1+y}Se_{x}Te_{1-x} single crystals by magnetic susceptibility, muon spin rotation, and neutron diffraction. We find three regimes of behavior in the phase diagram for 0\leq x\leq 0.5: (i) commensurate magnetic order for x< 0.1, (ii) bulk superconductivity for $x\lesssim 0.1$, and (iii) a range \sim 0.25\leq x\leq 0.45 in which superconductivity coexists with static incommensurate magnetic order. The results are qualitatively consistent with a two-band mean-field model in which itinerant magnetism and extended s-wave superconductivity are competing order parameters.Comment: 4 pages, 4 figure