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Fluctuation-enhanced electron-phonon coupling in FeSe

Jovan Blagojević1, Ana Milosavljević1,*, Tea Belojica1, Bojana Višić1,2, Marko Opačić1, Andrijana Šolajić1, Jelena Pešić1, Enrico Di Lucente3, Novica Paunović1 et al.

Milorad V. Milošević4,5, Emil S. Bozin1, Aifeng Wang6, Cedomir Petrovic7,8,9,10, Zoran V. Popović11, Rudi Hackl12,13, and Nenad Lazarević1

  • *Contact author: ana.milosavljevic@ipb.ac.rs
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Phys. Rev. B 114, 235105 – Published 5 October, 2026

DOI: https://doi.org/10.1103/yhzg-7n5t

Abstract

The interactions among lattice, charge, and spin degrees of freedom fundamentally shape material properties. In FeSe, symmetry-breaking perturbations serve as highly sensitive probes of these couplings. Previous work has shown that defects and isoelectronic substitution can substantially alter these interactions, giving rise to additional phonon modes. In this study, uniaxial strain is employed as a tunable symmetry-breaking control parameter to probe the intrinsic lattice response in the absence of disorder. The temperature evolution of phonon excitations was examined with a temperature resolution of 3 K in the vicinity of the nemato-structural transition temperature Ts, under strain applied along the 〈110〉 and 〈100〉 crystallographic directions. A subtle asymmetry of the A1gph mode appears in the unstrained crystal within a narrow temperature window around Ts, originating from the emergence of an additional mode in the fully symmetric channel. With applied strain, this feature becomes more distinctly resolved. The anomaly is attributed to modifications of the coupling between lattice and electronic degrees of freedom driven by the ordering fluctuations right above the nematic transition. These fluctuations may enhance the susceptibility of the electron-lattice system and enable two-phonon Raman scattering involving the acoustic mode near the X and R points. The presence of this two-phonon scattering depends on both the strength and the direction of the applied strain, indicating a high sensitivity of FeSe to local symmetry breaking.

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Phys. Rev. B 114, 235105– Published 5 October, 2026
  • Received 20 April 2026
  • Revised 9 August 2026
  • Accepted 11 September 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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