Abstract
The breakdown of the lattice translational invariance symmetry
that occurs at complex oxide interfaces may profoundly
modify their electronic structure, leading to interfacial states
with properties drastically different from those of the superlattice
individual components. The appearance of a conducting
two dimensional (2D) electron gas at the interface between two
insulating oxides and induced magnetism in a non-magnetic
material are just two among many fascinating examples. [ 1–8 ]
One of the key factors underlying novel properties is the modifi
cation of the doping and orbital occupancy near those interfaces,
which may result from charge transfer processes. [ 3 , 9–11 ]
If materials used in heterostructures have different work functions,
a non-equilibrium situation will be created at the interface
and charge will be transferred until the chemical potential
levels off. [ 12 ] The use of such phenomena to modify doping in
heterostructures has been proposed theoretically as a new route
to avoid the quenched disorder that inevitably accompanies the
chemical doping. At the interface between a Mott insulating
parent compound of the high critical temperature superconductor
(HTSC) family and a suitable material that would act
as the charge donor, electron doped phases could be stabilized
which would eventually turn metallic and perhaps superconducting.
[ 12 , 13 ] Such charge transfer processes have been observed
at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 /
YBa 2 Cu 3 O 7 , [ 14 ] La 2−x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1−x Nb x O 3 /
Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found
at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping
by charge transfer could not be examined in the other two cases
due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity
of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in
one case and due to the conducting nature of the SrTi 1−x Nb x O 3
in the other case, which obscures changes in the conducting
properties of the interface layer.
In this paper, the structural and
