Visualizing Band Selective Enhancement of Quasiparticle Lifetime in a Metallic Ferromagnet

Result of the Month

Author: Adam Kaminski Institute: ''Ames Laboratory'' Nature Communications
Date: 3/2022
Instruments: DA30-L

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.

Here, we investigate a FM variant of EuCd2As2, which has received much attention recently as a candidate magnetic Weyl semimetal displaying FM or antiferromagnetic order which can be controlled by doping. These unique properties make FM-EuCd2As2 an ideal candidate for such studies. We show that its electronic quasiparticles experience a significant lifetime enhancement in certain bands and energy ranges. We associate this effect with the emergence of different impurity and magnetic scattering rates for majority and minority carriers due to distinct phase spaces of the respective scattering processes. This demonstrates the complexity and importance of magnetic coupling to itinerant carriers and establishes a direct connection between quasiparticle properties and transport behavior in metallic FMs.

Figure 1: Electronic structure and Fermi surface cuts of EuCd2As2 from ARPES and DFT in para- and FM phase, crystal structure, and resistivity.

Figure Description: a Crystal structure of EuCd2As2. b Temperature-dependent normalized resistivity, ρ(T)/ρ(300K), where ρ(300K) ≈ 4 × 10−4 ω cm. c, d FS results from ARPES measurements at 40 and 10 K, respectively, where TC = 26 K is FM transition temperature. e, f ARPES intensity along the black dashed lines in (c, d) measured at 40 and 10 K, respectively. The orange arrow points to the bands crossing the Fermi level; the green arrow points to the fully occupied hole band at the center; the black arrow points to a possible splitting of the bands at 40 K. The color scale shows relative photoelectron intensity in panels (c–f). g, h FS calculated using DFT in paramagnetic and FM states, respectively. Color scale shows probability of finding available electronic state. i, j Band dispersion from DFT calculations along the black dashed line in (c). Bands undergo approximately k-independent rigid (Zeeman) energy shifts in the FM phase.

Figure 2: Detailed temperature evolution of the electronic structure of EuCd2As2 obtained using ARPES.

Figure Description: a MDCs at the Fermi energy measured at temperatures between 5 and 60 K. The dashed lines are a guide to eye-marking locations of MDC peaks. Comparing peak position at T ≥ 25 K and T = 5 K, note that hole peak (spin) splits into two peaks in opposite directions. b EDCs at ky = 0 at temperatures between 5 and 50 K. Black lines mark locations of peaks. Note that the central peak is (spin) split into two at low temperatures. c Full-width half maximum (FWHM) data obtained from Lorentzian fits to the MDCs for the inner hole band showing significant reduction of scattering (enhancement of lifetime) for energies slightly above the top of the fully occupied band, which are marked by arrows. d The binding energy of the fully occupied hole band top as a function of temperature. e, f MDCs at 5 and 15 K, respectively, for the right side of hole bands close to energies marked as blue stars in Fig. 2; −0.02 to −0.20 eV with 0.02 eV steps. Blue stars indicate the peak position. MDCs for which the two peaks merge are marked in blue. g FWHM of the MDC peaks on the left side in (a) as a function of temperature. Red triangles represent the very left peak (broad outer band), and black squares represent the second left peak (sharp inner band). Error bars represent the standard deviation of fitting the width of the peaks. The solid lines are theory results of the spin-dependent scattering rates of minority (red) and majority (black) carriers. We find good agreement under the assumption that the width in energy and in momentum space is proportional to each other.

ARPES measurements

Samples used for ARPES measurements were cleaved in situ at 40 K under ultrahigh vacuum (UHV). The data were acquired using a tunable VUV laser ARPES system that consists of Scienta Omicron DA30-L electron analyzer, a picosecond Ti:Sapphire oscillator, and fourth harmonic generator20. Data were collected with photon energies of 6.05–6.79 eV. Momentum and energy resolutions were set at ~0.005 Å−1 and 2 meV. The size of the photon beam on the sample was ~30 μm. The measurements were reproduced using several single crystals and extensive temperature cycling to exclude possibility of sample aging effects.



Na Hyun Jo, Yun Wu, Thaís V. Trevisan, Lin-Lin Wang, Kyungchan Lee, Brinda Kuthanazhi, Benjamin Schrunk, S. L. Bud’ko, P. C. Canfield, P. P. Orth & Adam Kaminski


1. Division of Materials Science and Engineering, Ames Laboratory, Ames, IA, 50011, USA

Na Hyun Jo, Yun Wu, Thaís V. Trevisan, Lin-Lin Wang, Kyungchan Lee, Brinda Kuthanazhi, Benjamin Schrunk, S. L. Bud’ko, P. C. Canfield, P. P. Orth & Adam Kaminski

2. Department of Physics and Astronomy, Iowa State University, Ames, IA, 50011, USA

Na Hyun Jo, Yun Wu, Thaís V. Trevisan, Kyungchan Lee, Brinda Kuthanazhi, Benjamin Schrunk, S. L. Bud’ko, P. C. Canfield, P. P. Orth & Adam Kaminski


Jo, N.H., Wu, Y., Trevisan, T.V. et al. Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet. Nat Commun 12, 7169 (2021).