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Correlated electronic states at a ferromagnetic oxide interface

D. Jones, A. Weh, A. Östlin, D. Braak, T. Kopp, P. Seiler, U. Eckern, L. Chioncel

Abstract

We propose a minimal tight-binding model for the electronic interface layer of the LaAlO$_3$/SrTiO$_3$ heterostructure with oxygen vacancies. In this model, the effective carriers are subject to oxygen vacancy induced magnetic impurities. Both the effects of random on-site potentials and Zeeman-like exchange interactions between correlated carriers and magnetic impurities are taken into account. By applying the combined coherent potential approximation (CPA) and dynamical mean-field theory (DMFT) for a ferromagnetic state, we uncover a disordered Fermi-liquid regime for the majority-spins and a low energy scale which controls the transport of the minority-spin carriers, both induced by the magnetic impurities.

Correlated electronic states at a ferromagnetic oxide interface

Abstract

We propose a minimal tight-binding model for the electronic interface layer of the LaAlO/SrTiO heterostructure with oxygen vacancies. In this model, the effective carriers are subject to oxygen vacancy induced magnetic impurities. Both the effects of random on-site potentials and Zeeman-like exchange interactions between correlated carriers and magnetic impurities are taken into account. By applying the combined coherent potential approximation (CPA) and dynamical mean-field theory (DMFT) for a ferromagnetic state, we uncover a disordered Fermi-liquid regime for the majority-spins and a low energy scale which controls the transport of the minority-spin carriers, both induced by the magnetic impurities.
Paper Structure (7 sections, 7 equations, 5 figures)

This paper contains 7 sections, 7 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Interface Model Hamiltonian
  3. CPA+DMFT computations for the Hubbard model
  4. Results
  5. Spectral functions and Self-energies
  6. Impurity state conductivity computation
  7. Discussion and Conclusions

Figures (5)

  • Figure 1: Left: The interface TiO$_2$-layer containing randomly distributed oxygen vacancies (OV). Right: Mapping onto an effective model of the molecular orbitals type-$\rm A=O-Ti-O$ (green) and type-$\rm B= O-Ti-VO$ (red). A "local moment" is induced by vacancies at the B-sites.
  • Figure 2: Alloy component DOS ($\mathrm{d}_{\mathrm{xy}}$-$80\%$-dashed lines and $\tilde{\mathrm{e}}_{\mathrm{g}}$-$20\%$-solid lines). Non-interacting results $U=0$ (black) and $U=0.5D = t^*$ (blue) at the inverse temperature $\beta=20 / D$.
  • Figure 3: The imaginary part of the retarded self-energy $\Sigma^R_{c}$ computed using CPA+DMFT for $U=0.5D = t^*$ and $\beta=20/D$. The inset shows the self-energy around the Fermi level.
  • Figure 4: Orbital resolved density of states for various values of $U$ computed with CPA+DMFT at the inverse temperature $\beta=20 / D$.
  • Figure 5: The inverse of the Drude peak $\rho_0 = 1 / \sigma(0, T)$ in dependence on temperature $T^2$ for the minority spin channel of the guest $\mathrm{\tilde{e}_{g}}$ orbital (B) computed with CPA+DMFT. The solid lines are linear fits of $\rho_0$.