Largely enhanced electron-phonon coupling in the superconductors HfRuP and ZrRuAs

Abstract

HfRuP and ZrRuAs have garnered significant interest in recent years as potential topological superconductors. However, the mechanism underlying their superconducting pairing, particularly whether it is mediated by electron-phonon coupling (EPC), remains unresolved. Here, we conducted polarized and temperature-dependent Raman scattering experiments to comparatively investigate their EPC. Six Raman-active phonon modes were assigned for each compound based on polarized Raman spectra and first-principles calculations. Temperature-dependent Raman scattering measurements revealed a large and continuous softening of some low-energy phonon modes for both crystals in the measurement temperature range from 1.7to300K. In HfRuP, the E″ (91.5cm−1) and E′ (102.9cm−1) modes exhibit phonon softening and linewidth broadening upon cooling. In ZrRuAs, the E″ (88.8cm−1) mode shows similar behavior. Furthermore, the E′ mode in HfRuP (357.2cm−1) and the A1′ mode in ZrRuAs (171.1cm−1) exhibit conventional frequency hardening but anomalous linewidth broadening upon cooling. Our first-principles calculations attribute these anomalies to a resonancelike enhancement of the EPC between the Fermi-surface electrons and the Ru-dominated E″ phonon mode. The electronic band structures also demonstrate that the enhancement stems from the exact matching in energy scale between the Ru-dominated low-frequency phonon modes and the distribution of their electronic densities of states around EF. These results provide direct evidence that EPC drives the superconducting pairing in both compounds, highlighting the pivotal role of Ru atoms in these ternary transition metal pnictide superconductors.

Source-reported materials — not catalogue approval

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