Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet

Abstract

Electrons navigate more easily in a background of ordered magnetic moments than around randomly oriented ones. This fundamental quantum mechanical principle is due to their Bloch wave nature and also underlies ballistic electronic motion in a perfect crystal. As a result, a paramagnetic metal that develops ferromagnetic order often experiences a sharp drop in the resistivity. Despite the universality of this phenomenon, a direct observation of the impact of ferromagnetic order on the electronic quasiparticles in a magnetic metal is still lacking. Here we demonstrate that quasiparticles experience a significant enhancement of their lifetime in the ferromagnetic state of the low-density magnetic semimetal EuCd2As2, but this occurs only in selected bands and specific energy ranges. This is a direct consequence of the magnetically induced band splitting and the multi-orbital nature of the material. Our detailed study allows to disentangle different electronic scattering mechanisms due to non-magnetic disorder and magnon exchange. Such high momentum and energy dependence quasiparticle lifetime enhancement can lead to spin selective transport and potential spintronic applications.

Anomalous Hall Conductivity and Nernst Effect of the Ideal Weyl Semimetallic Ferromagnet EuCd2As2

“…This is consistent with our DFT calculations and previously report by Jo et al. [ 31 ] Earlier in PM‐EuCd 2 As 2 , the splitting of energy bands was observed due to FM fluctuations that were spatially correlated. [ 26 ] According to our calculations, the distance between two Weyl point is about ≈0.05 Å, which is very hard to resolve in ARPES spectra.…”

“…[31] By comparing the ARPES spectra taken at 18 K (Figure 3e) and 43 K (Figure 3f), which are in the FM and paramagnetic (PM) states, respectively, we observed significant differences in the band structure. This is consistent with our DFT calculations and previously report by Jo et al [31] Earlier S10a and S11b, Supporting Information). The red solid curve is the dispersion from the ARPES along the Γ-M direction (Figure 3e).…”

“…EuCd 2 As 2 split into majority and minority spin bands as a result of FM transition. [ 31 ] By comparing the ARPES spectra taken at 18 K (Figure 3e) and 43 K (Figure 3f), which are in the FM and paramagnetic (PM) states, respectively, we observed significant differences in the band structure. This is consistent with our DFT calculations and previously report by Jo et al.…”

“…In response to decreasing temperatures, Zeeman splitting becomes stronger as the internal field increases (i.e., the FM order parameter). [ 31 ] Therefore, splitting decreases with increasing temperature and disappears at FM transition temperatures.…”

Anisotropic magnetism and electronic structure of trigonal EuAl$_2$Ge$_2$ single crystals

“…Quasiparticle enhancement in magnetically-ordered states has been reported in other magnetic materials due to the decrease of spin fluctuations and changes in the scattering mechanism [52,53]. Further zooming the ARPES spectra in momentum reveals that the individual hole-like bands actually split in two.…”