上海科技大学知识管理系统

Here we use low-temperature scanning tunneling microscopy to study the pnictide superconductor, BaNi2As2, which goes through a tetragonal to triclinic phase transition at ~136 K. In the triclinic phase, we observe the quasiparticle interference and the unidirectional charge density wave (CDW) with Q = 1/3 on the Ba surface of BaNi2As2. On the NiAs surface, apart from the unidirectional CDW, there are structural-modulation-induced chain-like superstructures with distinct periodicities. These complex chain-like structures can be along different lattice directions, which forms two domain structures. The unidirectional CDW appears more prominent in the NiAs domain where it is perpendicular to the chain-like superstructures. In the tetragonal phase, the Q = 1/3 unidirectional CDW disappears on both the Ba and the NiAs surfaces, and the NiAs surface appears as the ordered atomic chains with the 1 × 2 periodicity. Our results provide important insights for the interplay among the structural modulation, the unidirectional CDW and the nematicity in this class of materials.