Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of electron-doped cuprate superconductor Sr0.9La0.1CuO2Sr_{0.9}La_{0.1}CuO_2

We present the first demonstration of vortices in an electron-type cuprate superconductor, the highest $T_c$ (= 43 K) electron-type cuprate $Sr_{0.9}La_{0.1}CuO_2$. Our spatially resolved quasiparticle tunneling spectra reveal a hidden low-energy pseudogap inside the vortex core and unconventional spectral evolution with temperature and magnetic field. These results cannot be easily explained by the scenario of pure superconductivity in the ground state of high-$T_c$ superconductivity.Comment: 6 pages, 4 figures. Two new graphs have been added into Figure 2. Accepted for publication in Europhysics Letters. Corresponding author: Nai-Chang Yeh (E-mail: [email protected]

Scanning Tunneling Spectroscopic Studies of the Effects of Dielectrics and Metallic Substrates on the Local Electronic Characteristics of Graphene

Atomically resolved imaging and spectroscopic characteristics of graphene grown by chemical vapor deposition (CVD) on copper foils are investigated and compared with those of mechanical exfoliated graphene on SiO_2. For exfoliated graphene, the local spectral deviations from ideal behavior may be attributed to strain induced by the SiO_2 substrate. For CVD grown graphene, the lattice structure appears strongly distorted by the underlying copper, with regions in direct contact with copper showing nearly square lattices whereas suspended regions from thermal relaxation exhibiting nearly honeycomb or hexagonal lattice structures. The electronic density of states (DOS) correlates closely with the atomic arrangements of carbon, showing excess zero-bias tunneling conductance and nearly energy-independent DOS for strongly distorted graphene, in contrast to the linearly dispersive DOS for suspended graphene. These results suggest that graphene can interact strongly with both metallic and dielectric materials in close proximity, leading to non-negligible modifications to the electronic properties

On the methanol emission detection in the TW Hya disc: the role of grain surface chemistry and non-LTE excitation

The recent detection of gas-phase methanol (CH$_3$OH) lines in the disc of TW Hya by Walsh et al. provided the first observational constraints on the complex O-bearing organic content in protoplanetary discs. The emission has a ring-like morphology, with a peak at $\sim 30-50$ au and an inferred column density of $\sim 3-6\times10^{12}$ cm$^{-2}$. A low CH$_3$OH fractional abundance of $\sim 0.3-4\times 10^{-11}$ (with respect to H$_2$) is derived, depending on the assumed vertical location of the CH$_3$OH molecular layer. In this study, we use a thermo-chemical model of the TW Hya disc, coupled with the ALCHEMIC gas-grain chemical model, assuming laboratory-motivated, fast diffusivities of the surface molecules to interpret the CH$_3$OH detection. Based on this disc model, we performed radiative transfer calculations with the LIME code and simulations of the observations with the CASA simulator. We found that our model allows to reproduce the observations well. The CH$_3$OH emission in our model appears as a ring with radius of $\sim60$ au. Synthetic and observed line flux densities are equal within the rms noise level of observations. The synthetic CH$_3$OH spectra calculated assuming local thermodynamic equilibrium (LTE) can differ by up to a factor of 3.5 from the non-LTE spectra. For the strongest lines, the differences between LTE and non-LTE flux densities are very small and practically negligible. Variations in the diffusivity of the surface molecules can lead to variations of the CH$_3$OH abundance and, therefore, line flux densities by an order of magnitude.Comment: Accepted for publication in MNRAS, 8 pages, 8 figure

Scanning tunneling spectroscopic evidence for magnetic field-induced microscopic orders in the high-TcT_c superconductor YBa2_2Cu3_3O7−δ_{7-\delta}

We report spatially resolved tunneling spectroscopic evidence for field-induced microscopic orders in a high-$T_c$ superconductor $\rm YBa_2Cu_3O_{7-\delta}$. The spectral characteristics inside vortices reveal a pseudogap ($V_{\rm CO}$) larger than the superconducting gap ($\Delta\_{\rm SC}$) as well as a subgap ($\Delta\^{\prime}$) smaller than $\Delta\_{\rm SC}$, and the spectral weight shifts steadily from $\Delta_{\rm SC}$ to $V_{\rm CO}$ and $\Delta\^{\prime}$ upon increasing magnetic field. Additionally, energy-independent conductance modulations at 3.6 and 7.1 lattice constants along the Cu-O bonding directions and at 9.5 lattice constants along the nodal directions are manifested in the vortex state. These wave-vectors differ fundamentally from the strongly dispersive modes due to Bogoliubov quasiparticle scattering interferences and may be associated with field-induced microscopic orders of pair-, charge- and spin-density waves.Comment: Paper updated and accepted for publication in Europhysics Letters. 4 figures and 6 pages. Corresponding author: Nai-Chang Yeh (E-mail: [email protected]

Probation occupational cultures for the future? A focus group discussion

This article is based on a discussion, between the four co-authors, that took place over two days during the 'Conversation with Paul Senior' in Kendal in January 2016. Conscious that we have each undertaken research into aspects of occupational cultures in probation and social work, we spent some time on the first day devising questions that we might ask ourselves in order to imagine what occupational cultures in Probation might be like in 2020. The following day, we decided that an innovative way to capture our musings might be to imagine ourselves as a focus group and to record our discussion. So this is what we did - using nothing more than a smartphone. Subsequently, the recording was transcribed and we set about editing it to form the core of this article. We have added an introduction and a conclusion but the core discussion is very much as it was - 'warts and all'. We are aware that the arguments are not always presented in a polished fashion but we have resisted tampering too much with the spontaneity of the discussion. Our aim is to provide a few insights and stimulate further debate and research. © 2016 Sheffield Hallam University, Sheffield

Evidence for Strain-Induced Local Conductance Modulations in Single-Layer Graphene on SiO_2

Graphene has emerged as an electronic material that is promising for device applications and for studying two-dimensional electron gases with relativistic dispersion near two Dirac points. Nonetheless, deviations from Dirac-like spectroscopy have been widely reported with varying interpretations. Here we show evidence for strain-induced spatial modulations in the local conductance of single-layer graphene on SiO_2 substrates from scanning tunneling microscopic (STM) studies. We find that strained graphene exhibits parabolic, U-shaped conductance vs bias voltage spectra rather than the V-shaped spectra expected for Dirac fermions, whereas V-shaped spectra are recovered in regions of relaxed graphene. Strain maps derived from the STM studies further reveal direct correlation with the local tunneling conductance. These results are attributed to a strain-induced frequency increase in the out-of-plane phonon mode that mediates the low-energy inelastic charge tunneling into graphene