  We investigate the spectral and transport properties of parallel
double-quantum-dot (DQD) system with interdot tunneling coupling in both the
equilibrium and nonequilibrium cases. The special geometry of DQD system is
considered, in which each dot is connected to two leads by the tunneling
barriers. With the help of Keldysh nonequilibrium Green function technique and
the equation-of-motion approach, the spectral function and the conductance
spectra of DQD system are calculated in two cases with and without the intradot
Coulomb interaction, respectively. The exact calculation is performed in the
absence of intradot Coulomb interaction. For the case with intradot Coulomb
interaction, the Hartree-Fock approximation is applied to truncate the equation
of motion for the high-order Green functions at high temperatures. The
phenomenon of correlated electron transport is clearly shown in the linear
conductance of each dot in the presence of interdot tunneling when setting one
dot level and tuning another. The interplay between the intradot Coulomb
interaction and the interdot tunneling coupling is displayed.
