Real-space Observation of Unidirectional Charge Density Wave and Complex Structural Modulation in the Pnictide Superconductor Ba${}_{1-x}$Sr${}_x$Ni${}_2$As${}_2$

Abstract

Here we use low-temperature and variable-temperature scanning tunneling microscopy to study the pnictide superconductor, Ba${}_{1-x}$Sr${}_x$Ni${}_2$As${}_2$. In the low-temperature phase (triclinic phase) of BaNi${}_2$As${}_2$, we observe the unidirectional charge density wave (CDW) with $Q$ = 1/3 on both the Ba and NiAs surfaces. On the NiAs surface of the triclinic BaNi${}_2$As${}_2$, there are structural-modulation-induced chain-like superstructures with distinct periodicities. In the high-temperature phase (tetragonal phase) of BaNi${}_2$As${}_2$, the NiAs surface appears as the periodic 1 by 2 superstructure. Interestingly, in the triclinic phase of Ba${}_{0.5}$Sr${}_{0.5}$Ni${}_2$As${}_2$, the unidirectional CDW is suppressed on both the Ba/Sr and NiAs surfaces, and the Sr substitution stabilizes the periodic 1 by 2 superstructure on the NiAs surface, which enhance the superconductivity in Ba${}_{0.5}$Sr${}_{0.5}$Ni${}_2$As${}_2$. Our results provide important microscopic insights for the interplay among the unidirectional CDW, structural modulation, and superconductivity in this class of pnictide superconductors.

15 pages, 4 figures

References in corpus (12)

• Theory of Intertwined Orders in High Temperature Superconductors
• First Order Phase Transition and Superconductivity in BaNi2As2 Single Crystals
• Structure and Anisotropic Properties of BaFe2-xNixAs2 (x = 0, 1, 2) Single Crystals
• Density functional study of BaNi${}_2$As${}_2$: Electronic structure, phonons and electron-phonon superconductivity
• Giant Phonon Softening and Enhancement of Superconductivity by Phosphorus Doping of BaNi2As2
• Multiple charge density waves and superconductivity nucleation at antiphase domain walls in the nematic pnictide Ba${}_{1-x}$Sr${}_x$Ni${}_2$As${}_2$
• An Electronic Nematic Liquid in BaNi${}_2$As${}_2$
• Electronic structure of BaNi${}_2$As${}_2$
• Soft-phonon and charge-density-wave formation in nematic BaNi${}_2$As${}_2$
• Rotational symmetry breaking at the incommensurate charge-density-wave transition in Ba(Ni,Co)${}_2$(As,P)${}_2$: Possible nematic phase induced by charge/orbital fluctuations
• Phonon softening and slowing down of charge-density-wave fluctuations in BaNi${}_2$As${}_2$
• Complex structure due to As bonding and interplay with electronic structure in superconducting BaNi2As2

Cited by in corpus (4)

• Pressure-induced Superconductivity in Zintl Topological Insulator SrIn2As2
• Perspective: imaging atomic step geometry to determine surface terminations of kagome materials and beyond
• Spectral Evidence for Unidirectional Charge Density Wave in Detwinned BaNi${}_2$As${}_2$
• Coexistence of stripe order and superconductivity in NaAlSi