Using low-temperature ultrahigh vacuum scanning tunneling microscopy (STM) we have obtained real-space images showing orbital order on a Co-terminated surface of CeCoIn5, which is a heavy-fermion superconducting material. Because of the 4-fold symmetry, 3dxz and 3dyz orbitals of the Co atoms are energetically degenerated. However, on the surface, because of the reduced coordination number and resulting enhanced electron correlation, the capability of the electron screening is suppressed. As a result, in order to reduce the Coulomb repulsive energy alternating unoccupation of the two 3d...
