  We report scanning tunneling spectroscopic studies of cuprate and
iron-arsenic superconductors, including YBa_2Cu_3O_{7-\delta} (Y-123, T_c = 93
K), Sr_{0.9}La_{0.1}CuO_2 (La-112, T_c = 43 K), and the "122" compounds
Ba(Fe_{1-x}Co_x)_2As_2 (Co-122 with x = 0.06, 0.08, 0.12 for T_c = 14, 24, 20
K). For H > 0, pseudogap (\Delta_{PG}) features are revealed inside the
vortices, with \Delta_{PG} = [(\Delta_{eff})^2+(\Delta_{SC})^2]^{1/2} >
\Delta_{SC} in Y-123 and \Delta_{PG} < \Delta_{SC} in La-112, suggesting that
the physical origin of \Delta_{PG} is a competing order coexisting with
superconductivity. Additionally, Fourier transformation (FT) of the Y-123
spectra exhibits two types of spectral peaks, one type is associated with
energy (\omega)-dependent quasiparticle interference (QPI) wave-vectors and the
other consists of \omega-independent wave-vectors due to competing orders and
(\pi,\pi) magnetic resonances. For the multi-band Co-122 compounds, two-gap
superconductivity is found for all doping levels. Magnetic resonant modes that
follow the temperature dependence of the superconducting gaps are also
identified. These findings, together with the \omega- and x-dependent QPI
spectra, are consistent with a sign-changing s-wave pairing symmetry in the
Co-122 iron arsenides. Our comparative studies suggest that the commonalities
among the cuprate and the ferrous superconductors include the proximity to
competing orders, antiferromagnetic (AFM) spin fluctuations and magnetic
resonances in the superconducting (SC) state, and the unconventional pairing
symmetries with sign-changing order parameters on different parts of the Fermi
surface.
