Atomic-scale visualization of surface-assisted orbital order

Kim, H.*; Yoshida, Yasuo*; Lee, C.-C.*; Chang, T.-R.*; Jeng, H.-T.*; Lin, H.*; Haga, Yoshinori   ; Fisk, Z.*; Hasegawa, Yukio*

We report a first, real-space, imaging of an orbital ordered structure on a cobalt-terminated surface of the well-studied heavy fermion compound CeCoIn. Within small tip-sample distances, the cobalt atoms on a cleaved (001) surface take on dumbbell shapes alternatingly aligned in the [100] and [010] directions in scanning tunneling microscopy topographies. First-principles calculations reveal that this staggered orbital order is triggered by enhanced on-site Coulomb interaction at the surface.