Sublattice symmetry breaking and Kondo-effect enhancement in strained graphene

Abstract

Kondo physics in doped monolayer graphene is predicted to exhibit unusual features due to the linear vanishing of the pristine material's density of states at the Dirac point. Despite several attempts, conclusive experimental observation of the phenomenon remains elusive. One likely obstacle to identification is a very small Kondo temperature scale TK in situations where the chemical potential lies near the Dirac point. We propose tailored mechanical deformations of monolayer graphene as a means of revealing unique fingerprints of the Kondo effect. Inhomogeneous strains are known to produce specific alternating changes in the local density of states (LDOS) away from the Dirac point that signal sublattice symmetry breaking effects. Small LDOS changes can be amplified in an exponential increase or decrease of TK for magnetic impurities attached at different locations. We illustrate this behavior in two deformation geometries: a circular "bubble" and a long fold, both described by Gaussian displacement profiles. We calculate the LDOS changes for modest strains and analyze the relevant Anderson impurity model describing a magnetic atom adsorbed in either a "top-site" or a "hollow-site" configuration. Numerical renormalization-group solutions of the impurity model suggest that higher expected TK values, combined with distinctive spatial patterns under variation of the point of graphene attachment, make the top-site configuration the more promising for experimental observation of signatures of the Kondo effect. The strong strain sensitivity of TK may lift top-site Kondo physics into the range experimentally accessible using local probes such as scanning tunneling microscopy.

Electron transport properties of graphene nanoribbons with Gaussian deformation

“…This type of Gaussian deformation generates a fold along the y-direction. Such a deformation has been discussed recently about valley filtering properties [34] and Kondo effect under a magnetic impurity in 2D graphene Submitted to Arxiv on 08 May 2020 structures [28]. To understand if the formation of a transport gap is also observed in graphene ribbons with this kind of Gaussian deformation, we examined the electronic properties of several Gaussian fold deformed ribbons.…”

“…On the other hand, the presence of out-of-plane deformation has been evidenced in many structures [24]. This kind of disorder has been examined recently on both 2D graphene [24][25][26][27][28] and ribbons [29][30][31]. It has been shown that graphene deposited on a low-quality substrate can contain out-of-plane deformations, and Gaussian deformations are frequently observed [24].…”

Observation of critical magnetic behavior in 2D carbon based composites

“…An enhanced Kondo effect was seen in strained graphene. 97 In comparison to Co films, Co/graphene shows a larger perpendicular magnetic anisotropy when compressive and tensile strain is applied. Yang et al revealed that the tensile strain effect arises from an increase in the hybridization between the same spin d xy and d x 2 – y 2 states of the surface Co film.…”

On the propagation of Dirac fermions in graphene with strain-induced inhomogeneous Fermi velocity

“…Indeed, strains or folds of graphene sheet can be used to create waveguides [2], [10], [11], [12], [13]. They can also lead to collimation, focusing or valley polarization of electron beams [2], [10], [14], or to the Kondo effect [15].…”