Kondo Quantum Criticality of Magnetic Adatoms in Graphene

TL;DR

This paper explores the quantum critical behavior of magnetic adatoms in graphene, revealing a new class of critical points with unique scaling laws and potential experimental access via gating and scanning probes.

Contribution

It predicts a novel class of quantum critical points in graphene with distinct scaling and screening properties, expanding understanding of Kondo physics in two-dimensional materials.

Findings

Kondo temperature scales as |J-J_c|^{1/3} near critical coupling

RKKY interaction decays as 1/R^7 in this class

Quantum criticality can be tuned by gating in graphene

Abstract

We examine the exchange Hamiltonian for magnetic adatoms in graphene with localized inner shell states. On symmetry grounds, we predict the existence of a class of orbitals that lead to a distinct class of quantum critical points in graphene, where the Kondo temperature scales as $T_{K}\propto|J-J_{c}|^{1/3}$ near the critical coupling $J_{c}$, and the local spin is effectively screened by a \emph{super-ohmic} bath. For this class, the RKKY interaction decays spatially with a fast power law $\sim1/R^{7}$. Away from half filling, we show that the exchange coupling in graphene can be controlled across the quantum critical region by gating. We propose that the vicinity of the Kondo quantum critical point can be directly accessed with scanning tunneling probes and gating.