  Since its discovery as a Kondo insulator 50 years ago, SmB6 recently received
a revival of interest due to detection of unexpected quantum oscillations in
the insulating state, discovery of disorder-immune bulk transport, and
proposals of correlation-driven topological physics. While recent transport
results attribute the anomalous low temperature conduction to two-dimensional
surface states, important alternatives, such as conduction channel residing in
one-dimensional dislocation lines, have not been adequately explored. Here we
study SmB6 with scanning microwave impedance microscopy and uncover evidence
for conducting one-dimensional states terminating at surface step edges. These
states remain conducting up to room temperature, indicating unusual robustness
against scattering and an unconventional origin. Our results bring to light a
heretofore undetected conduction route in SmB6 that contributes to the low
temperature transport. The unique scenario of intrinsic one-dimensional
conducting channels in a highly insulating correlated bulk offers a
one-dimensional platform that may host exotic physics.
