  Present work demonstrates the formation of spin-orbital polarons in electron
doped copper oxides, that arise due to doping-induced polarisation of the
oxygen orbitals in the CuO$_2$ planes. The concept of such polarons is
fundamentally different from previous interpretations. The novel aspect of
spin-orbit polarons is best described by electrons becoming self-trapped in
one-dimensional channels created by polarisation of the oxygen orbitals. The
one-dimensional channels form elongated filaments with two possible
orientations, along the diagonals of the elementary CuO$_2$ square plaquette.
As the density of doped electrons increases multiple filaments are formed.
These may condense into a single percollating filamentary phase. Alternatively,
the filaments may cross perpendicularly to create an interconnected conducting
quasi-one-dimensional web. At low electron doping the antiferromagnetic (AFM)
state and the polaron web coexist. As the doping is increased the web of
filaments modifies and transforms the AFM correlations leading to a series of
quantum phase transitions - which affect the normal and superconducting state
properties.
