Anomalous\nElectron–Phonon Coupling in Cubic\nBe–X (X = Co, Ni, Rh, Hf) Crystals and Insight from Fermi Surface\nNesting and Phonon Bandgap

The electronic contribution significantly\ndominates thermal transport\nfor most pure metallic systems, while the phononic (lattice) contribution\nremains relatively small. We report four metallic materials, namely\ncubic BeCo, BeNi, BeRh, and BeHf, which are screened by our recent\ndeep learning approach from Open Quantum Materials Database, all possessing\nlarge phonon bandgaps and phonon anomaly features. Employing first-principles\ncalculations to solve the phonon Boltzmann transport equation, we\nreport that at room temperature, the phononic thermal conductivity\nof these Be–X compounds is exceptionally high, rivaling that\nof diamond. Specifically, the thermal conductivities are 2117 W/mK\nfor BeCo, 2243 W/mK for BeNi, 2368 W/mK for BeRh, and 1600 W/mK for\nBeHf. This remarkable thermal performance is attributed to the large\nphonon bandgaps and phonon anomaly features present in these materials.\nFurthermore, when electron–phonon coupling is accounted for,\nthe phononic thermal conductivities of the Be–X compounds experience\na reduction by approximately 2 orders of magnitude. Notably, BeHf\npresents an exceptional case, with its phononic thermal conductivity\nmeasured at 68 W/mK. This value is several times to an order of magnitude\nhigher than the typical range observed in most metals and metallic\nsystems, which generally lies between 2 and 18 W/mK. Quantitative\nanalysis of phonon lifetime, Eliashberg spectral function, and Fermi\nsurface show that the Be–X systems have strong electron–phonon\ncoupling which originates from their Fermi surface nesting. However,\nthe phonon anomalies of BeHf are shallower, which weakens the electron–phonon\ncoupling and results in the abnormally high phononic thermal conductivity\nof BeHf. This research enhances our comprehension of various heat\nconduction phenomena in crystals, particularly offering a method to\nidentify new materials with phonon-mediated thermal transport in metals\nand metallic systems for innovative applications in the future.