  Charge transport in the hole-doped quasi-1D model system
Y$_{2-x}$Ca$_x$BaNiO$_5$ (x $ leq$ 0.15) is investigated in the 50-300 K
temperature range. The resistivity temperature dependence is characterized by a
constant activation energy $E_{a}/k_{B} sim$ 1830 K at room temperature while
$E_{a}$ decreases upon cooling. We suggest that $E_{a}$ measures the binding
energy of the doped holes which form magneto-acoustic polarons when polarizing
the neighboring Ni spins. A semi-classical model is proposed which allows to
relate the electrical measurements and the bulk magnetic susceptibility. This
model gives a picture of the spin-charge-lattice relation in this
inhomogeneously doped quasi-1D system and explains its unusual one-particle
charge excitation spectrum close to the Fermi level.
