Spin dynamics of 3d and 4d impurities embedded in prototypical topological insulators

Abstract

Topological insulators are insulating bulk materials hosting conducting surface states. Their magnetic doping breaks time-reversal symmetry and generates numerous interesting effects such as dissipationless transport. Nonetheless, their dynamical properties are still poorly understood.Here, we perform a systematic investigation of transverse spin excitations of 3d and 4d single impurities embedded in two prototypical topological insulators (Bi 2 Te 3 and Bi 2 Se 3 ). The impurityinduced states within the bulk gap of the topological insulators are found to have a drastic impact on the spin excitation spectra, resulting in very high lifetimes reaching up to microseconds. An intuitive picture of the spin dynamics is obtained by mapping onto a generalized Landau-Lifshitz-Gilbert phenomenological model. The first quantity extracted from this mapping procedure is the magnetic anisotropy energy, which is then compared to the one provided by the magnetic force theorem. This uncovers some difficulties encountered with the latter, which can provide erroneous results for impurities with a high density of states at the Fermi energy. Moreover, the Gilbert damping and nutation tensors are obtained. The nutation effects can lead to a non-negligible shift in the spin excitation resonance in the high-frequency regime. Finally, we study the impact of the surface state on the spin dynamics, which may be severely altered due to the repositioning of the impurity-induced state in comparison to the bulk case. Our systematic investigation of this series of magnetic impurities sheds light on their spin dynamics within topological insulators, with implications for available and future experimental studies as, for instance, on the viability of using such impurities for solid-state qubits. arXiv:1812.09596v1 [cond-mat.mes-hall]

Spontaneous and externally driven quantum spin fluctuations of 3d and 4d single atoms adsorbed on graphene

“…In addition to using band-energy differences, the MAE can alternatively be obtained from the static transverse magnetic susceptibility, calculated within linear response theory, as 56 . The values obtained using this approach are also given in Table II and illustrated in Fig.…”

“…The two methods disagree when sharp features are present near the Fermi energy in the density of states. This causes large changes in the electronic structure when rotating the magnetic moment, which invalidates the use of the magnetic force theorem 56 . Fe and Mo are the most affected elements (see Fig.…”

Controlling the real-time dynamics of a spin coupled to the helical edge states of the Kane-Mele model

“…The real-time dynamics of magnetic impurities at surfaces of topological insulators has been studied to a lesser extent. Recent studies have employed time-dependent density-functional theory [37] and, for periodically driven impurities, Floquet theory [38]. The effects of a single TRS-breaking magnetic impurity on the transport properties of a KM zigzag ribbon mediated by the helical edge states have been studied within scattering theory [39].…”