Non-linear anomalous Edelstein response at altermagnetic interfaces

Abstract

In altermagnets, time-reversal symmetry breaking spin-polarizes electronic states, while total magnetization remains zero. In addition, at altermagnetic surfaces Rashba-spin orbit coupling is activated due to broken inversion symmetry, introducing a competing spin-momentum locking interaction. Here we show that their interplay leads to the formation of complex, chiral spin textures that offer novel, non-linear spin-to-charge conversion properties. Whereas altermagnetic order suppresses the canonical linear in-plane Rashba-Edelstein response, we establish the presence of an anomalous transversal Edelstein effect for planar applied electric and magnetic field, or alternatively, an in-plane magnetization. Moreover the non-linear Edelstein response resulting purely from electric fields also triggers the anomalous out-of-plane magnetization. We determine the anomalous response with a model based on the ab-initio electronic structure of RuO$_2$ bilayers, ultimately opening experimental avenues to explore spin-charge conversion phenomena at altermagnetic interfaces.

Figures (15)

• Figure 1: Schematic representation of the transversal, non-linear altermagnetic EE. (a) Out-of-plane spin arrangement in the absence of driving current with zero net magnetization and (b) homogeneous tilting of the out-of-plane spins due to an in-plane driving current that generates a transverse magnetic field.
• Figure 2: Competing altermagnetic and Rashba spin-orbit interactions. (a) Electronic dispersion resulting from the continuum Hamiltonian \ref{['eq:ham_altermagnets_rashba']}$\alpha=52$ meV Å. (b) Fermi surface and spin structure for fixed chemical potential (dashed line in panel (a)). (c) linear Edelstein susceptibility $\chi_{xy}/\chi_0$ ($\chi_0=2.44\times10^{2}$$\mu_B$ Å V$^{-1}$) for different $\alpha$. The dashed lines correspond to the pure RSOC case ($\gamma=0$).
• Figure 3: Bilayer of RuO$_2$ and its electronic structure density-functional calculations. (a) Crystal structure. (b) Band structure along high symmetry points indicated in (c).
• Figure 4: Anomalous non-linear EE due to a combined planar magnetic and electric field. (a) Electronic dispersion from Hamiltonian \ref{['eq:ham_altermagnets_rashba']} with $\alpha=52$ meV Å and $h_y=40$ meV. (b) Fermi surface and spin structure for fixed chemical potential, see the dashed line in (a). (c) Edelstein response $\chi_{xi}/\chi_0$ ($\chi_0=2.44\times10^{2}$$\mu_B$ Å V$^{-1}$) for the directions $i={x,y,z}$. The green dashed line corresponds to the pure RSOC case ($\gamma=h_y=0$).
• Figure 5: Second-order electric Edelstein response. $\tilde{\chi}_{xxz}/\tilde{\chi}_0$ (with $\tilde{\chi}_0=2.36 \times 10^{6} \,\text{\AA}^2\text{V}^{-2}$) versus $\mu$ for different values of $\alpha$.