Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic (STS) studies of electron-doped cuprate superconductor La$_{0.1}$Sr $_{0.9}$CuO$_{2}$ (La-112)

We present STS studies on the electron-doped cuprate superconductor La-112 as a function of magnetic field (H). The spatially resolved spectra manifest vortices, and the average vortex lattice constant scales consistently with Abrikosov's theory. A hidden pseudogap (V$_{CO})$ smaller than the superconducting gap ($\Delta _{SC})$ is revealed inside the vortex core, and the core radius is comparable to the superconducting coherence length \textit{$\xi $}$_{ab}$ = 4$.$86 nm. Analysis of the energy histograms reveals that $\Delta _{eff}$, where $\Delta _{eff}$=[($\Delta _{SC})^{2 }$+ (V$_{CO})^{2}$]$^{1/2}$, shifts downward with increasing H from $\Delta _{eff}$= 12.2 $\pm $ 0.8 meV at H = 0 to a base value of V$_{CO}$=8.5 $\pm $0.6 meV at H $>$ 0. This finding differs from the behavior of conventional superconductors where the vortex-state spectral weight would shift continuously to lower energies with increasing H and show peaks at zero energy due to suppression of $\Delta _{SC}$ inside vortices. Finally, Fourier transformation of the vortex-state tunneling spectra will be reported and compared with results from other cuprates. Ref.: Teague et al., arxiv:0809.0541. Work supported by NSF Grant DMR-0405088.