We present an atomic resolution scanning tunneling spectroscopy study of superconducting BaFe1.8Co0.2As2 single crystals in magnetic fields up to 9 T. At zero field, a single gap with coherence peaks at Delta=6.25 meV is observed in the density of states. At 9 and 6 T, we image a disordered vortex lattice, consistent with isotropic, single flux quantum vortices. Vortex locations are uncorrelated with strong-scattering surface impurities, demonstrating bulk pinning. The vortex-induced subgap density of states fits an exponential decay from the vortex center, from which we extract a coherence length xi=27.6+/-2.9 A, corresponding to an upper critical field Hc2=43 T.

The unclear relationship between cuprate superconductivity and the pseudogap state remains an impediment to understanding the high transition temperature (T(c)) superconducting mechanism. Here, we used magnetic field-dependent scanning tunneling microscopy to provide phase-sensitive proof that d-wave superconductivity coexists with the pseudogap on the antinodal Fermi surface of an overdoped cuprate. Furthermore, by tracking the hole-doping (p) dependence of the quasi-particle interference pattern within a single bismuth-based cuprate family, we observed a Fermi surface reconstruction slightly below optimal doping, indicating a zero-field quantum phase transition in notable proximity to the maximum superconducting T(c). Surprisingly, this major reorganization of the system's underlying electronic structure has no effect on the smoothly evolving pseudogap.

A nanomechanical testing set-up is developed by integrating an atomic force microscope (AFM) for force measurements with a scanning electron microscope (SEM) to provide imaging capabilities. Electrospun nanofibers of polyvinyl alcohol (PVA), nylon-6 and biological mineralized collagen fibrils (MCFs) from antler bone were manipulated and tensile-tested using the AFM-SEM set-up. The complete stress-strain behavior to failure of individual nanofibers was recorded and a diversity of mechanical properties observed, highlighting how this technique is able to elucidate mechanical behavior due to structural composition at nanometer length scales.

Tremendous excitement has followed the recent discovery of superconductivity up to T c = 56 K in iron-arsenic based materials (pnictides). This discovery breaks the monopoly on high-T c superconductivity held by copper-oxides (cuprates) for over two decades and renews hope that high-T c superconductivity may finally be theoretically understood and widely applied.Since scanning tunneling microscopy (STM) and spectroscopy (STS) have been key tools in the investigation and understanding of both conventional and unconventional superconductivity, these techniques are also applied to the pnictides. While the field is still in its early stages, several important achievements by STM and STS have been reported on the pnictides. In this paper, we will review their contribution towards an understanding of superconductivity in this new class of materials.

Strong electronic distortions are typically accompanied by structural distortions, and vice versa. Determining the relationship between these orders can be complicated, but a clue comes from their (co-)dependence on other parameters. In a cuprate superconductor, for example, both superconductivity and the pseudogap are highly dependent on doping, temperature, and magnetic field. Here, we investigate whether the structural symmetry in BSCCO is similarly dependent on these parameters, or whether it is an omnipresent background within which the electronic states evolve.Structural symmetries are traditionally measured by scattering experiments, such as xray or neutron scattering to determine bulk symmetries, or low energy electron diffraction (LEED) to determine surface symmetries. The structure of double layer Bi 2 Sr 2 CaCu 2 O 8+x (Bi-2212) is sketched in Fig. 1a. Although nearly tetragonal, a ∼0.5% difference between a and b axes 14 makes the true structure orthorhombic. However, despite numerous scattering experiments on BSCCO spanning two decades, the more detailed structure has remained enigmatic, due in part to an incommensurate structural "supermodulation" which pervades the bulk of these materials 14 , and to dopant disorder which leads Bi atoms to stochastically occupy inequivalent sites in different unit cells 15 . [18][19][20][21][22][23] . Thus, to investigate the role of structure in these broken symmetry electronic states, it is imperative to make atomic scale measurements of the structural symmetry.To undertake this investigation, we use three different home-built scanning tunneling microscopes. In each case, a sample is cleaved at low temperature in cryogenic ultra-high vacuum, and immediately inserted into the scanning head. BSCCO typically cleaves between two BiO mirror planes (Fig. 1a). Data was acquired at T=6K unless otherwise noted. The tip is rastered across the sample surface, while a feedback loop adjusts its height to maintain a constant tip-sample tunneling current. This results in a topographic image of the BiO surface.Temperature drift (typically < 10 mK), piezo hysteresis, and piezo nonlinearity, can lead to small but problematic warping of topographic images. Recently, Lawler et al introduced a ground-breaking algorithm to correct these picometer-scale drifts 7 . We show that Lawler's algorithm can also be used to remove subtle periodic noise (see Supplementary that the pseudogap is characterized by intra-unit-cell inversion symmetry breaking? To investigate this, we characterize the dependence of the structural distortion on parameters which are known to heavily influence electronic ordered states: doping, temperature, and magnetic field. Fig. 3a locates in a three-dimensional phase diagram the 21 datasets in which we measured the structure. The key results are summarized in Figs. 3b-d. We do not find a dependence of the structural distortion on doping, temperature, or field, across a wide range of values. We have measured the distortion both inside and outside the superconducting...