Pressure-driven enhancement of phonon contribution to the thermal conductivity of Iridium

Understanding the microscopic dynamics of the fundamental energy carriers in condensed matter under extreme pressure conditions can reveal insights into unique physical phenomena that are otherwise not easily discernible at ambient conditions. Here, by utilizing a combination of machine learning interatomic potential (MLP)-based molecular dynamics simulations to calculate phonon thermal conductivity and parameter -free first -principles calculations of electron-phonon coupling and electronic thermal conductivity, we show that (contrary to typical elemental metals) the phonon contribution to the total thermal conductivity in iridium can be increased from 18% at ambient conditions to 40% at 60 GPa hydrostatic pressure conditions. The strength of electron-phonon scattering, as quantified by the mass enhancement parameter, decreases monotonically with pressure resulting in an increase in the lifetime of electrons around the Fermi energy. This consequently leads to a monotonic increase in the electron thermal conductivity from 134 W m -1 K -1 at ambient to 177 W m -1 K -1 at 60 GPa. Similarly, the phonon thermal conductivity has a relatively higher increase from 30 W m -1 K -1 at ambient to 120 W m -1 K -1 at 60 GPa. This is attributed to considerable phonon hardening and increase in the group velocity of the heat carrying phonons with pressure. Along with the pronounced phonon contributions to the total thermal conductivity, we also show that the temperature dependence of the phonon thermal conductivity at ambient pressure is dictated by higher -order phonon interactions (beyond the typical three -phonon processes) in iridium.