Theory of spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

TL;DR

This paper presents a theoretical analysis of using time-resolved scanning tunneling spectroscopy to study the spin dynamics of magnetic adatoms, demonstrating control and probing of spin relaxation via voltage pulses.

Contribution

It introduces a nonperturbative scattering theory model for analyzing spin dynamics of magnetic adatoms under voltage pulses in STM, validated against experiments.

Findings

Demonstrates control of adatom spin states with voltage pulses.

Shows how relaxation dynamics are reflected in tunneling current.

Provides numerical results consistent with experimental data.

Abstract

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. Here we analyze theoretically this novel tool 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 nonpertubative and hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the prediction of simple analytical models and compared with experiments.