Abstract
Inelastic scanning tunneling microscopy (STM) has recently been shown (Loth et al 2010 Science329 1628) to be extendable to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze this novel tool theoretically by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump–probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is non-perturbative and, hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the predictions of simple analytical models and compared with experiments.
Highlights
MODEL HAMILTONIANWhich describes the tunneling electrons (with a mass m and momentum operator p) emanating from the tip and are subject to the magnetic field B
The inelastic scanning tunneling microscopy (STM) has been shown recently (Loth et al Science 329, 1628 (2010)) to be extendable as to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules
In the present method we focus on the description of the tunneling starting from a model Hamiltonian including the magnetic anisotropy, the exchange coupling and the coupling to the external magnetic field
Summary
Which describes the tunneling electrons (with a mass m and momentum operator p) emanating from the tip and are subject to the magnetic field B. The red arrow denotes the expectation value of the spin S. picture of extended states (tunneling electrons) coupled to a localized magnetic moment. The total effective potential experienced by the tunneling electrons VB(x) + χν, ↑ |Hint|χν, ↑ is different for the ground state ν = 1 and the first excited state ν = 2, as sketched in figure 1 (b) (the tip spin is ↑ in both cases). We find the tunneling probability to scatter from the tip electron with a spin state |τ into |σ and from the surface spin state |χν into |χμ by taking the absolute value of the S-matrix (equation (5)). We trace out the spin |σ of the tunneling tip electron This yields the reduced density matrix of the surface spin. The formula (11) is evaluated by (i) propagating the initial product state, (ii) calculating the overlap with the final state on the right side of the barrier, and (iii) by performing a Fourier transformation
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