Real-Space Observation of Unidirectional Charge Density Wave and Complex Structural Modulation in the Pnictide Superconductor Ba<sub>1-<i>x</i></sub>Sr<sub><i>x</i></sub>Ni<sub>2</sub>As<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 37011415.
- Also identified by DOI 10.1021/acs.nanolett.3c00323.
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Abstract
Here we use low-temperature and variable-temperature scanning tunneling microscopy to study the pnictide superconductor, Ba<sub>1-<i>x</i></sub>Sr<sub><i>x</i></sub>Ni<sub>2</sub>As<sub>2</sub>. In the low-temperature phase (triclinic phase) of BaNi<sub>2</sub>As<sub>2</sub>, we observe the unidirectional charge density wave (CDW) with <i>Q</i> = 1/3 on both the Ba and NiAs surfaces. On the NiAs surface of the triclinic BaNi<sub>2</sub>As<sub>2</sub>, there are structural-modulation-induced chain-like superstructures with distinct periodicities. In the high-temperature phase (tetragonal phase) of BaNi<sub>2</sub>As<sub>2</sub>, the NiAs surface appears as the periodic 1 × 2 superstructure. Interestingly, in the triclinic phase of Ba<sub>0.5</sub>Sr<sub>0.5</sub>Ni<sub>2</sub>As<sub>2</sub>, the unidirectional CDW is suppressed on both the Ba/Sr and NiAs surfaces, and the Sr substitution stabilizes the periodic 1 × 2 superstructure on the NiAs surface, which enhance the superconductivity in Ba<sub>0.5</sub>Sr<sub>0.5</sub>Ni<sub>2</sub>As<sub>2</sub>. Our results provide important microscopic insights for the interplay among the unidirectional CDW, structural modulation, and superconductivity in this class of pnictide superconductors.