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Orbital Ordering in the Charge Density Wave Phases of BaNi2(As1−xPx)2

Tom Lacmann1,2,*, Robert Eder1, Igor Vinograd1,†, Michael Merz1,3, Mehdi Frachet1,‡, Philippa Helen McGuinness1, Kurt Kummer4, Enrico Schierle5, Amir-Abbas Haghighirad1 et al.

Sofia-Michaela Souliou1 and Matthieu Le Tacon1,§

  • *Contact author: Tom.Lacmann@epfl.ch
  • †Present address: Université Grenoble Alpes, INSA Toulouse, Université de Toulouse Paul Sabatier, CNRS, LNCMI, F-38000 Grenoble, France.
  • ‡Present address: CNRS, Université Grenoble Alpes, Institut Néel, 38042 Grenoble, France.
  • §Contact author: Matthieu.LeTacon@kit.edu
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Phys. Rev. Lett. 136, 036504 – Published 23 January, 2026

DOI: https://doi.org/10.1103/x5bv-w84m

Abstract

We use resonant x-ray scattering at the nickel L2,3 edges to investigate the interplay between orbital degrees of freedom and charge density waves (CDWs) in the superconductor BaNi2(As1−xPx)2. Both the incommensurate and commensurate CDWs in this system exhibit strong resonant enhancement with distinct energy and polarization dependencies, indicative of orbital ordering. Azimuthal-angle-dependent measurements reveal a lowering of the local Ni site symmetry, consistent with monoclinic or lower point group symmetry. The scattering signatures of both CDWs are dominated by contributions from Ni dxz,yz orbitals, with similar orbital character despite their distinct wave vectors. These findings point to a shared orbital-driven formation mechanism and provide new insight into the symmetry breaking and orbital and nematic fluctuations in the high-temperature regime of the superconductor BaNi2(As1−xPx)2.

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Phys. Rev. Lett. 136, 036504– Published 23 January, 2026
  • Received 19 August 2025
  • Revised 10 November 2025
  • Accepted 16 December 2025
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