  Correlation functions and low-energy excitations are investigated in the
asymmetric two-leg ladder consisting of a Hubbard chain and a noninteracting
tight-binding (Fermi) chain using the density matrix renormalization group
method. The behavior of charge, spin and pairing correlations is discussed for
the four phases found at half filling, namely, Luttinger liquid, Kondo-Mott
insulator, spin-gapped Mott insulator and correlated band insulator.
Quasi-long-range antiferromagnetic spin correlations are found in the Hubbard
leg in the Luttinger liquid phase only. Pair-density-wave correlations are
studied to understand the structure of bound pairs found in the Fermi leg of
the spin-gapped Mott phase at half filling and at light doping but we find no
enhanced pairing correlations. Low-energy excitations cause variations of spin
and charge densities on both legs that demonstrate the confinement of the
lowest charge excitations on the Fermi leg while the lowest spin excitations
are localized on the Hubbard leg in the three insulating phases. The velocities
of charge, spin, and single-particle excitations are investigated to clarify
the confinement of elementary excitations in the Luttinger liquid phase. The
observed spatial separation of elementary spin and charge excitations could
facilitate the coexistence of different (quasi-)long-range orders in
higher-dimensional extensions of the asymmetric Hubbard ladder.
