Zhanyang Hao, Haohao Sheng, Wanru Ma, Wen-Gen Zheng, Yongqing Cai, Zijuan Xie, Wanlin Cheng, Zuowei Liang, Wu Xie, Weidong Zhao, C B Liu, Zhibin Su, Junhao Lin, Liusuo Wu, Zhengtai Liu, Mao Ye, J. Dai, Massimo Tallarida, Shengtao Cui, Yogendra Kumar, K. Shimada, Kenichi Ozawa, Shuki Torii, Kazuhiro MORI, Y D Xie, Junze Deng, Jiaou Wang, Xuetao Zhu, Jiandong Guo, Jia‐Wei Mei, Zhenyu Wang, Xianhui Chen, Ping Miao, Zhijun Wang, Kai Chen
Orbital order describes a quantum state where occupied orbitals line up in a periodic pattern. Although orbital physics plays a fundamental and universal role in strongly correlated electron systems, the existence and particularly the band-structure fingerprint of orbital order remain a long-standing mystery. Here we report the discovery of rare earth 5d-orbital order developed by the surface states of the intermetallic compound Tb2CoAl4Ge2. Angle-resolved photoemission spectroscopy reveals characteristic nematic features such as Fermi surface deformation and band splitting. These experimental observations can be described by a ferro-orbital order term in the mean-field Hamiltonian. The structural and magnetic origin of such order is excluded by systematic high-resolution neutron powder diffraction and scanning tunnelling microscopy measurements. Our results provide strong evidence for a pure surface orbital order scenario avoiding complications from structural distortion as in colossal magnetoresistance manganites, magnetic order as in iron-based superconductors and charge transfer p-orbital order in cuprates. Whether orbital order can exist with a clear band-structure fingerprint in correlated materials has remained unresolved. Now an orbital order from rare earth 5d electrons without structural or magnetic order is seen in an intermetallic compound.