Longitudinal and transverse spin relaxation times of magnetic single adatoms: an ab initio analysis

TL;DR

This paper uses ab initio methods to analyze the vastly different timescales of longitudinal and transverse spin relaxation in magnetic adatoms, revealing femtosecond and picosecond regimes and proposing ultrafast laser techniques for measurement.

Contribution

It provides the first ab initio analysis of both longitudinal and transverse spin relaxation times in magnetic adatoms, highlighting their distinct energy scales and timescales.

Findings

$T_{ot}$ is of order picoseconds, matching experimental data.

$T_{ot} \\gg T_{\parallel}$, with $T_{\parallel}$ in femtoseconds.

Ultrafast laser pulses are needed to measure $T_{\parallel}$.

Abstract

We present a systematic ab initio investigation of the longitudinal and transverse spin relaxation times of magnetic single adatoms deposited on metallic substrates. Our analysis based on time-dependent density functional theory shows that the longitudinal time, $T_{\parallel}$, is of order femtosecond while the transverse time, $T_{\perp}$, is of order picosecond, i.e. $T_{\perp}\gg T_{\parallel}$. This comes as a consequence of the different energy scales of the corresponding processes: $T_{\parallel}$ involves spin-density excitations of order eV, while $T_{\perp}$ is governed by atomic spin-excitations of order meV. Comparison to available inelastic scanning tunneling spectroscopy $\mathrm{d}I/\mathrm{d}V$ experimental curves shows that the order of magnitude of $T_{\perp}$ agrees well with our results. Regarding $T_{\parallel}$, the time scale calculated here is several orders of magnitude faster than what has been measured up to now; we therefore propose that an ultrafast laser pulse measuring technique is required in order to access the ultrafast spin-dynamics described in this work.