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Comparative Raman study of Ruddlesden-Popper nickelates and the monolayer-trilayer polymorph

Vignesh Sundaramurthy1, Abhi Suthar1, Pascal Puphal1, Congcong Le2, Yuhao Gu3, Hasan Yilmaz1,4, Pablo Sosa-Lizama1, Peter A. van Aken1, Y. Eren Suyolcu1 et al.

Masahiko Isobe1, Andreas P. Schnyder1, Xianxin Wu5, Matteo Minola1, Bernhard Keimer1, and Matthias Hepting1,*

  • *Contact author: hepting@fkf.mpg.de
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Phys. Rev. B 114, 295106 – Published 6 November, 2026

DOI: https://doi.org/10.1103/m2js-yzky

Abstract

Ruddlesden-Popper (RP) nickelates have attracted intense interest following the discovery of superconductivity in several members of the series, including bilayer (BL) La3Ni2O7, trilayer (TL) La4Ni3O10, and structural polymorphs composed of monolayer-bilayer or monolayer-trilayer (ML-TL) units. However, an inherent propensity of the RP series to form intergrown phases during single-crystal synthesis, together with spatial variations in oxygen stoichiometry, has complicated the determination of their intrinsic material properties. As a consequence, conflicting reports have emerged on both their electronic phase transitions and lattice dynamics. In this work, we perform a comparative study of the phononic and electronic Raman responses of high-quality ML-TL single crystals and contrast them with those of the other RP nickelates, using samples with optimized oxygen content. We establish several Raman spectral features that enable unambiguous phase identification across the series. Moreover, we uncover characteristics in the phononic and electronic Raman response of ML-TL that are not reflected in the pure ML and TL compounds. We attribute these differences to a distinctive electronic structure arising from self-doping and confinement effects induced by the ML unit within the ML-TL lattice architecture.

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Phys. Rev. B 114, 295106– Published 6 November, 2026
  • Received 19 February 2026
  • Revised 13 August 2026
  • Accepted 20 October 2026
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