Renormalization of single-ion magnetic anisotropy in the absence of the Kondo effect

Abstract

Inelastic spin flip excitations associated with single-ion magnetic anisotropy of quantum spins, can be strongly renormalized by Kondo exchange coupling to the conduction electrons in the substrate, as shown recently for the case of Co adatoms on CuN2 islands. In this case differential conductance spectra show zero-bias anomalies due to a Kondo effect of the doubly degenerate ground state, and finite-bias step features due to spin flip excitations. Here I consider spin-1 quantum magnets with positive uniaxial anisotropy, where the ground state is non-degenerate and hence the Kondo effect does not take place. Nevertheless the renormalization of inelastic spin excitations due to exchange coupling by hybridization of the quantum spin with the conduction electrons still takes place despite the complete absence of the Kondo effect in the ground state. Additionally, I show that away from particle-hole symmetry, charge fluctuations have a similar effect to Kondo exchange coupling, leading to the renormalization of spin flip excitations. However, in contrast to the renormalization by Kondo exchange, charge fluctuations lead to asymmetric spectra, which for strong charge fluctuations can mimic Fano behavior. arXiv:1712.01005v2 [cond-mat.mes-hall]

Electrically Addressing the Spin of a Magnetic Porphyrin through Covalently Connected Graphene Electrodes

“…At this point, charge fluctuations are fully suppressed (N d = 2). Still, the value∆ 0 is slightly smaller than the bare MAE of ∆ 0 = D = 7.14meV due to renormalization by Kondo exchange coupling with the conduction electrons [14,31].…”

“…In this scenario, spin-fluctuations caused by the Kondo effect are not possible due to the lack of GS degeneracy. However, charge fluctuations are still possible and become important as electron occupation changes and the system approaches towards a mix-valence regime, where MAE is renormalized and can acquire asymmetric lineshapes [31]. We simulated changes in orbital filling by shifting the impurity levels ε d downwards, resulting in the increase of electron occupation N d of the d-orbitals ( Figure 4a).…”

Spin dependent transmission of nickelocene-Cu contacts probed with shot noise

“…The reason for this intriguing behavior is that the magnetic anisotropy term ∼ DS 2 z is always reinforced at lower energies as was shown in previous works. 46,55,56 Thus Kondo screening actually does not take place in the model. In summary the model calculations show that dI/dV spectra recorded for systems which show the type B behavior in the conductance (Fig.…”

“…According to the DFT calculations the spin-1 of the Nc molecule responsible for the spin excitations is localized in the d xz -and d yz -orbitals of the Ni center, which are nearly degenerate. We hence model the system by a twoorbital Anderson impurity model including a magnetic anisotropy term 46,47 . The impurity part of the Hamiltonian is then given by:…”

“…Hence the degeneracy of the S = 1 triplet is partially lifted, the |m z = 0 singlet state becomes the ground state, and the |m z = ±1 states an excited doublet. Due to the lack of ground state degeneracy the Kondo effect is suppressed 46 .…”