Quantum half-orphans in kagome antiferromagnets

TL;DR

This study numerically investigates how non-magnetic impurities affect the magnetic response of kagome antiferromagnets across various spins, revealing emergent half-orphan degrees of freedom that significantly alter local susceptibility and ground state properties.

Contribution

It introduces the concept of half-orphan degrees of freedom in kagome antiferromagnets with impurities, showing their impact on magnetic response across different spin values.

Findings

Large enhancement of local susceptibility on triangles with two vacancies.

Lone spins behave as almost free spins in an effective magnetic field.

Ground state total spin trends towards S/2 for S ≥ 2.

Abstract

We numerically study the effects of non-magnetic impurities (vacancies) in the spin-$S$ Heisenberg antiferromagnet on the kagom\'e lattice. For a range of low but nonzero temperatures, and spin values that extend down to $S=2$, we find that the magnetization response to an external magnetic field is consistent with the response of emergent "half-orphan" degrees of freedom that are expected to dominate the response of the corresponding classical magnet in a similar temperature range whenever there are two vacancies on the same triangle. Specifically, for all spin values we have considered (from $S=1/2$ to $S=4$), there is a large enhancement of the local susceptibility of the lone spin on such a triangle with two vacancies; in the presence of a uniform magnetic field $h$, this lone-spin behaves effectively as an almost free spin $S$ in an effective field $h/2$. Quite remarkably, in the zero temperature limit, the ground state in the presence of a half-orphan has a non-zero total spin value $S_{GS}$ that shows a trend similar to $S/2$ when $S\ge 2$. These qualitative aspects of the response differ strikingly from the more conventional response of diluted samples without such half-orphan degrees of freedom. We discuss how these findings could be checked experimentally.