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Chemical enhancement of superconductivity in LaRu3Si2 with mode-selective coupling between kagome phonons and flat bands

Ryo Misawa1, Markus Kriener2, Rinsuke Yamada1, Ryota Nakano1, Milena Jovanovic2,3, Leslie M. Schoop2, and Max Hirschberger1,4,*

  • *Contact author: hirschberger@ap.t.u-tokyo.ac.jp
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Phys. Rev. Research 7, 033032 – Published 8 July, 2025

DOI: https://doi.org/10.1103/rnv1-rbw2

Abstract

In kagome metals, flat electronic bands induced by frustrated hopping are a platform for strong electron correlations. Here, we investigate the superconductivity in the kagome system LaRu3(Si1−xGex)2 by chemical pressure tuning while preserving the Ru-4d states that constitute the kagome flat bands. We observe a sizable enhancement in the density of states up to x=0.07, as determined by the specific heat, with a concomitant increase in the superconducting transition temperature Tc. Ge dopants induce a uniaxial lattice expansion along the c axis. Our first-principles calculations suggest that this mitigates the detrimental effect of hybridization between kagome layers and reduces the dispersion of the Ru-dx2−y2 flat band. The calculated chemical potential moves closer to the maximum in the energy-dependent density of states. Our result is consistent with a theoretical prediction of tunable flat-band superconductivity in LaRu3Si2 by mode-selective coupling between specific kagome phonons and the Ru-dx2−y2 orbitals.

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Phys. Rev. Research 7, 033032– Published 8 July, 2025
  • Received 20 February 2025
  • Revised 13 April 2025
  • Accepted 20 May 2025
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