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  • Open Access

Probing the symmetries of nodal-line semimetal SrAl4

Tomer Hasharoni1, Danila Sokratov2, Prathum Saraf2, Johnpierre Paglione2,3, and Alon Ron1,*

  • *Contact author: alonron@tauex.tau.ac.il
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Phys. Rev. Research 8, 043006 – Published 5 October, 2026

DOI: https://doi.org/10.1103/78p9-rjxz

Abstract

Symmetry plays a central role in determining the electronic structure and topology of nodal-line semimetals. SrAl4 is a nodal-line semimetal with tetragonal I4/mmm symmetry at room temperature, an incommensurate charge-density-wave transition at TCDW≃240K accompanied by C4 symmetry breaking, and a low-temperature monoclinic transition near T≃90K. Here, we use nonlinear optical second- and third-harmonic generation to track the evolution of crystal symmetries in SrAl4 with temperature and disorder. Temperature-dependent second-harmonic generation uncovers strong coupling between the lattice and the charge-density-wave order and shows that disorder quenches the low-temperature monoclinic phase. Room-temperature third-harmonic generation reveals broken C4 rotational symmetry in contrast to the reported tetragonal bulk structure, possibly due to a symmetry-lowered surface reconstruction. These results establish nonlinear harmonic generation as a sensitive probe of intertwined bulk and surface symmetry breaking in SrAl4 and as a complementary tool for refining symmetries where space group assignment through diffraction is ambiguous.

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Phys. Rev. Research 8, 043006– Published 5 October, 2026
  • Received 27 April 2026
  • Accepted 10 August 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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