  We study the low-energy limit of a quarter-filled one-dimensional Mott
insulator. We analytically determine the local density of states in the
presence of a strong impurity potential, which is modeled by a boundary. To
this end we calculate the Green function using field theoretical methods. The
Fourier transform of the local density of states shows signatures of a pinning
of the spin-density wave at the impurity as well as several dispersing features
at frequencies above the charge gap. These features can be interpreted as
propagating spin and charge degrees of freedom. Their relative strength can be
attributed to the "quasi-fermionic" behavior of charge excitations with equal
momenta. Furthermore, we discuss the effect of bound states localized at the
impurity. Finally, we give an overview of the local density of states in
various one-dimensional systems and discuss implications for scanning tunneling
microscopy experiments.
