Core Concepts
The dynamic RKKY interaction, derived from time-dependent fluctuations of the conduction electron spin susceptibility, retains sensitivity to time-reversal symmetry breaking that is lost in the static approximation. This enables the induction of spin chirality by external magnetic fields or through proximity to topologically nontrivial materials.
Abstract
The paper studies the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction in various Kondo lattice systems. It argues that the weak Kondo coupling expansion contains certain physics which is lost in the usual static approximation to the spin susceptibility. Notably, while the static approximation is blind to time-reversal symmetry breaking, the dynamic RKKY interaction is sensitive to it.
Using exact diagonalization on small systems and a large-N approximation on extended lattices, the paper explores the impact of dynamic RKKY interaction on spin liquids and spinons. On a honeycomb Kondo lattice with Haldane fluxes, it is shown that the dynamic RKKY can induce topological chiral spin states, generating non-trivial edge modes. This provides a mechanism to engineer Dzyaloshinskii-Moriya-like effects, even in centrosymmetric systems, opening avenues for the design of chiral spin liquids and topologically ordered states in Kondo lattices.
The paper also discusses the spinon lifetime and delocalization temperature in the weak Kondo coupling regime, finding that the dynamic RKKY interaction leads to a finite spinon lifetime and affects the onset of spinon delocalization compared to the static RKKY approximation. Additionally, the paper demonstrates that the dynamic RKKY interaction can induce spin chirality in a Kondo triangle setup by breaking time-reversal symmetry through an external magnetic field.
Stats
The paper presents the following key data and figures:
Fig. 2(a) shows the bandwidth of spinons (difference between maximum and minimum value of the real part of the self-energy) as a function of temperature for various values of the Kondo coupling strength J^2_K, exhibiting a mean-field-like delocalization transition.
Fig. 2(b) compares the spinon delocalization transition temperatures for both dynamic and static RKKY interactions as a function of J^2_K.
Fig. 3(a) shows the spin chirality on a Kondo triangle as a function of the magnetic flux threading the electrons, computed using exact diagonalization.
Fig. 3(b) presents the large-N results for the spin chirality on the Kondo triangle, confirming that the induced spin chirality is due to the dynamic RKKY interaction.
Fig. 4 depicts the spinon dispersion in a Kondo lattice with honeycomb geometry, where the time-reversal symmetry breaking in the conduction layer (induced by Haldane fluxes) is transferred to the spinons via the dynamic RKKY effect, opening a gap at the Dirac cones.
Quotes
"The dynamic RKKY interaction, derived from time-dependent fluctuations of the conduction electron spin susceptibility, retains certain key physical phenomena—such as sensitivity to time-reversal symmetry (TRS) breaking—that are lost in the static approximation."
"This tunable interaction provides a mechanism to engineer Dzyaloshinskii-Moriya-like effects, even in centrosymmetric systems, opening avenues for the design of chiral spin liquids and topologically ordered states in Kondo lattices."