  Pyrochlore oxides possessing "all-in-all-out" spin ordering have attracted
burgeoning interest as a rich ground of emergent states. This ordering has two
distinct types of magnetic domains (all-in-all-out or all-out-all-in) with
broken time-reversal symmetry, and a non-trivial metallic surface state has
been theoretically demonstrated to appear at their domain wall. Here, we report
on observation of this metallic conduction at the single
all-in-all-out/all-out-all-in magnetic domain wall formed at the
heterointerface of two pyrochlore iridates. By utilizing different
magnetoresponses of them with different lanthanide ions, the domain wall is
controllably inserted at the heterointerface, the surface state being detected
as anomalous conduction enhancement with a ferroic hysteresis. Our
establishment paves the way for further investigation and manipulation of this
new type of surface transport.
