Competing States in the Two-Dimensional Frustrated Kondo-Necklace Model

TL;DR

This study investigates the phase diagram of the two-dimensional frustrated Kondo-necklace model on a triangular lattice, revealing a direct transition between disordered and magnetic phases, and identifying a new competing ground state called the central spin phase.

Contribution

It provides the first unbiased iPEPS analysis showing the absence of partial Kondo screening in the isotropic limit and discovers a novel central spin phase competing with PKS.

Findings

No partial Kondo screening at I_z=0, phase transition observed.

Discovery of a new central spin (CS) phase with polarized spins.

Competition between PKS and CS phases for I_z > 0.

Abstract

The interplay between Kondo screening, indirect magnetic interaction and geometrical frustration is studied in the two-dimensional Kondo-necklace model on the triangular lattice. Using infinite projected entangled pair states (iPEPS), we compute the ground state as a function of the antiferromagnetic local Kondo interaction $J_K$ and the Ising-type direct spin-spin interaction $I_z$ . As opposed to previous studies, we do not find partial Kondo screening (PKS) in the isotropic limit $I_z = 0$ but the same behavior as in the unfrustrated case, i.e. a direct phase transition between the paradigmatic phases of the Doniach competition: (i) a disordered phase consisting of local spin-singlets at strong $J_K$ and (ii) a magnetically ordered phase at weak $J_K$ . For $I_z > 0$, we find a PKS ground state but again in opposite to previous studies, we find that the PKS ground state is in strong competition with a second ground state candidate not found before. This state is characterized by a strongly polarized central spin in each hexagon and its anti-parallel, weakly polarized (i.e. partially screened) neighbors. We name it central spin (CS) phase.