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Non-equilibrium correlation effects in spin transport through the 2D ferromagnet Fe$_4$GeTe$_2$

Declan Nell, Stefano Sanvito, Andrea Droghetti

Abstract

Understanding non-equilibrium spin transport through 2D ferromagnets is a theoretical challenge, as correlations produce a complex electronic structure with coexisting itinerant and localized electrons. We have developed a fully non-equilibrium ab initio method, combining density functional theory, dynamical mean-field theory, and non-equilibrium Green's functions to investigate the transport in Fe$_4$GeTe$_2$, a prototypical high-temperature 2D ferromagnet. We show that, while spin transport remains essentially single-particle under moderate bias, inelastic spin-dependent scattering of carriers with particle-hole excitations drives a distinctive hot-correlated electron regime beyond a critical voltage. This regime is marked by incoherent features in both the electronic spectrum and the conductance, which are experimentally accessible. Our results demonstrates that material-specific many-body non-equilibrium methods are essential for a complete understanding of spin transport in 2D ferromagnets.

Non-equilibrium correlation effects in spin transport through the 2D ferromagnet Fe$_4$GeTe$_2$

Abstract

Understanding non-equilibrium spin transport through 2D ferromagnets is a theoretical challenge, as correlations produce a complex electronic structure with coexisting itinerant and localized electrons. We have developed a fully non-equilibrium ab initio method, combining density functional theory, dynamical mean-field theory, and non-equilibrium Green's functions to investigate the transport in FeGeTe, a prototypical high-temperature 2D ferromagnet. We show that, while spin transport remains essentially single-particle under moderate bias, inelastic spin-dependent scattering of carriers with particle-hole excitations drives a distinctive hot-correlated electron regime beyond a critical voltage. This regime is marked by incoherent features in both the electronic spectrum and the conductance, which are experimentally accessible. Our results demonstrates that material-specific many-body non-equilibrium methods are essential for a complete understanding of spin transport in 2D ferromagnets.

Paper Structure

This paper contains 2 sections, 22 equations, 3 figures.

Table of Contents

  1. Acknowledgments
  2. End Matter

Figures (3)

  • Figure 1: Fe $3d$-PDOS and transmission coefficient at (a) 0 V, (b) 0.375 V and (c) 0.75 V, calculated with DFT (red line) and DMFT (blue line). Spin-up (down) values are shown positive (negative). The green vertical bars mark the bias window.
  • Figure 2: Self energies as a function of energy and bias. Top panels: real part of the retarded DMFT self-energy at zero bias and averaged over the Fe $3d$ orbitals, for the (a) spin-up and (b) spin-down channels. The orange line shows a linear fit around $E_\mathrm{F}$, with deviations indicating kinks. Bottom panels: the imaginary part of the retarded and lesser self-energy, averaged over the Fe $3d$ orbitals, for (c) spin-up and (d) spin-down channels at 0.375 V and 0.75 V.
  • Figure :