Momentum-dependent quasiparticle lifetime in ferromagnetic EuCd­₂As₂arising from spin-selective scattering

The development of long-range electronically ordered phases impacts the properties of quasiparticles in a material. In a ferromagnetic (FM) metal, the electronic bands are spin split due to an effective field caused by the magnetic order. The onset of FM order often results in a sharp decrease of resistivity because of a loss of spin-disorder scattering. Here, we report on a more direct observation of the effects of the coupling between electrons and ferromagnetic order via ARPES measurements in the newly discovered ferromagnetic metal EuCd₂As₂. Our study reveals a significant increase of the quasiparticle lifetime below the ferromagnetic transition temperature, yet only in selected bands and energy ranges. In particular, the majority band is observed to be much sharper than the minority band, which leads to spin selective transport behavior useful in spintronic applications. Using analytical theory, we show that the phenomenon can be naturally explained by spin-selective scattering and a competition between magnon and disorder scattering. Our theory can account for the momentum and energy dependence enhanced quasiparticle lifetime over a wide range of temperatures.