For a type-II superconductor, when the applied magnetic field is higher than the lower critical value H c1 , the magnetic flux will penetrate into the superconductor and form quantized vortices, which usually are arranged in an Abrikosov lattice. For the newly discovered iron pnictide superconductors, previous measurements have shown that, in electron-doped BaFe 2 As 2 , the vortices form a highly disordered structure 1-3 . In addition, the density of states (DOS) within the vortex cores 1 do not exhibit the Andreev bound states in conventional superconductors 4 -8 . In this Letter, we report the observation of a triangular vortex lattice and the Andreev bound states in hole-doped BaFe 2 As 2 by using a low temperature scanning tunneling microscope (STM). Detailed study of the vortex cores reveals that the spectrum of the Andreev bound states inside the vortex core exhibits a distinct spatial evolution: at the center of the vortex core, it appears as a single peak at 0.5 mV below the Fermi-energy; away from the core center, it gradually evolves into two sub-peaks and they eventually fade out. The drastic differences between the vortex cores of the electron-doped and hole-doped counterparts are illusive to the pairing mechanism of the iron pnictide superconductors.Magnetic flux quantization is one of the important quantum phenomena in the mixed

We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa2Cu3O6+x over a wide range of doping levels (0.1 ≤ x ≤ 1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002(2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed. PACS numbers:Electronic spin fluctuations are of central importance for current models of unconventional superconductivity in d-and f -electron compounds [1]. Inelastic neutron scattering (INS) provides comprehensive maps of the spin fluctuation intensity at energies and momenta that are well matched to the intrinsic collective response of correlated-electron systems, and has thus played a pivotal role in motivating and guiding theoretical work on unconventional superconductors [2]. Because of the limited intensity of primary neutron beams, however, INS can only be applied to materials of which large single crystals can be grown, and it is unsuitable as a probe of spin excitations in atomically thin heterostructures of complex materials, which provide perspectives for control -and ultimately design -of unconventional superconductivity [3].Resonant inelastic x-ray scattering (RIXS) at transition-metal L 2,3 -edges has recently emerged as a powerful momentum-resolved spectroscopic probe of collective spin excitations in crystals of sub-millimeter dimensions, and in thin films and multilayers [4,5]. Recent examples of RIXS studies of spin excitations include cuprates [6][7][8][9][10][11][12][13][14][15][16][17], iron-based superconductors [18] or iridates [19], where the intrinsic energy scale of the spin dynamics exceeds 100 meV. Initial RIXS data on the dispersion of magnons in the antiferromagnetic "parent compounds" of the cuprate high-temperature superconductors are fully consistent with prior INS data [6,12]. Remarkably, further RIXS studies revealed that magnon-like collective spin excitations persist in almost undiminished form even in optimally doped and overdoped cuprates, [12][13][14][15][16] where INS data are very limited. This indicates that strong electronic correlations persist even in a regime where Fermi-liquid properties have been well documented [20,21]. Motivated by these results, soft x-ray RIXS spectrometers with greatly enhanced resolution are currently under construction at many synchrotron facilities worldwide.To realize the potential of RIXS as a probe of unconventional superconductors and other correlated-electron systems, it is imperative to develop a quantitative...

A transient lateral photovoltaic effect (LPVE) has been observed in p-La0.7Sr0.3MnO3∕n-Si heterojunctions. Under the nonuniform irradiation of a pulsed laser, the LPVE shows high sensitivity to the spot position on the La0.7Sr0.3MnO3 surface. A mechanism based on the well established model for the LPVE in conventional semiconductors has been applied to explain the LPVE in the heteroepitaxial junctions of perovskite-type metal oxides. The large LPVE in the heteroepitaxial junctions is expected to make the perovskite-type metal oxide a new and faster candidate for position-sensitive photodetectors.

Recently, there have been increasingly hot debates on whether there exists a quantum spin liquid in the Kitaev honeycomb magnet α-RuCl_{3} in a high magnetic field. To investigate this issue, we perform ultralow-temperature thermal conductivity measurements on single crystals of α-RuCl_{3} down to 80 mK and up to 9 T. Our experiments clearly show a field-induced phase transition occurring at μ_{0}H_{c}≈7.5  T, above which the magnetic order is completely suppressed. The minimum of thermal conductivity at 7.5 T is attributed to the strong scattering of phonons by magnetic fluctuations. Most importantly, above 7.5 T, we do not observe any significant contribution of thermal conductivity from gapless magnetic excitations, which puts a strong constraint on the nature of the high-field phase of α-RuCl_{3}.

Ultrafast photoelectric effects have been observed in La0.7Sr0.3MnO3∕Si p-n junctions fabricated by laser molecular-beam epitaxy. The rise time was ∼210ps and the full width at half-maximum was ∼650ps for the photovoltaic pulse when the junction was irradiated by a 1064nm laser pulse of 25ps duration. The photovoltaic sensitivity was as large as 435mV∕mJ for a 1064nm laser pulse. No such photovoltaic signal was observed with irradiation from a 10.6μm CO2 laser pulse. The results reveal that this phenomenon is an ultrafast photoelectric effect.

The exact nature of the low temperature electronic phase of the manganite materials family, and hence the origin of their colossal magnetoresistant (CMR) effect, is still under heavy debate. By combining new photoemission and tunneling data, we show that in La 2-2x Sr 1+2x Mn 2 O 7 the polaronic degrees of freedom win out across the CMR region of the phase diagram. This means that the generic ground state is that of a system in which strong electron-lattice interactions result in vanishing coherent quasi-particle spectral weight at the Fermi level for all locations in k-space. The incoherence of the charge carriers offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopic data. The stacking number N is the key factor for true metallic behavior, as an intergrowth-driven breakdown of the polaronic domination to give a metal possessing a traditional Fermi surface is seen in the bilayer system.Competition between local lattice distortions leading to anti-ferromagnetic, charge and orbital (CO) ordering on the one hand, and mixed valence character promoting metallic ferromagnetic double exchange on the other, determines the transport transport properties LSMO [5], whereas the bilayer analogue is metallic only in a narrow Sr-doping and temperature regime [6], giving rise to the largest CMR effect [7]. The more strongly 2D, single layer compound shows neither metallic nor CMR behavior [8].Focusing on bilayer LSMO within the CMR-region of * These authors contributed equally to this work the phase diagram, the prevailing picture from structural studies is one of polarons existing above T C . On cooling towards T C , these short range versions of the CO order typical of the insulating compositions, become increasingly correlated [9, 10]. Eventually double exchange, leading to an itinerant, metallic state, takes over.This metallic state for x = 0.4 has been shown to support small quasi-particles (QPs) in the spectral function measured by angle-resolved photoemission (ARPES) [11]. These signal coherent electronic excitations, albeit strongly dressed with lattice distortions, and are seen as evidence for a novel and elusive state of matter known as a polaronic metal [11, 12].Other ARPES studies paint a different picture, with stronger QP features observed at low T that persist up to temperatures of order 1.5T C [13][14][15], despite the system being nominally insulating. In contrast, scanning tunneling microscopy / spectroscopy (STM/S) studies reported gaps in the local density of states near-E F for x = 0.30 [16] and 0.325 [17], both in the metallic and insulating temperature regimes. Finally, new neutron diffraction data for x = 0.4 has shown that even far below T C -at 10 K in the metallic state -polarons remain as fluctuations that strongly broaden and soften phonons near the wave vectors where the charge order peaks would appear in the insulating phase [18].Here, a combination of ARPES and STM/S reveals that the bilayer manganites still have a number of...

We report on low-temperature scanning tunneling microscopy and spectroscopy (STM) studies of the electronic structure of single-crystalline Ba 0.6 K 0.4 Fe 2 As 2. Multiple superconducting gaps are observed in the density of states (DOS) and the sizes of the two dominant gaps L and S are 7.6 and 3.3 meV, respectively. The flat bottom of the DOS spectra near zero bias indicates the nodeless feature of the gaps, while the global fitting to the spectra definitely requires the anisotropy. The nodeless gaps with finite anisotropy revealed in our STM data agree well with the expectations of an extended s-wave superconductivity.

An epidemiological design, consisting of cross-sectional (n = 2376) and cohort (n = 976) studies, was adopted to investigate the association between complement factors 3 (C3) and 4, and the metabolic syndrome (MetS) development. In the cross-sectional study, the C3 and C4 concentrations in the MetS group were higher than those in the non-MetS group (all P < 0.001), and the levels of immune globulin M (IgM), IgA, IgE, and IgG exhibited no significant differences between MetS and non-MetS (all P > 0.050). After multi-factor adjustment, the odds ratios (ORs) in the highest quartile of C3 and C4 concentrations were 7.047 (4.664, 10.648) and 1.961 (1.349, 2.849), respectively, both Ptrend < 0.050. After a 4 years follow-up, total 166 subjects were diagnosed with MetS, and the complement baseline levels from 2009 were used to predict the MetS risk in 2013. In the adjusted model, the relative risks (RRs) in the highest quartile of C3 and C4 levels were 4.779 (2.854, 8.003) and 2.590 (1.567, 4.280), respectively, both Ptrend < 0.001. Activation of complement factors may be an important part of inflammatory processes, and our results indicated that the elevated C3 and C4 levels were independent risk factors for MetS development.