Towards exact predictions of spin-phonon relaxation times: an ab initio implementation of open quantum systems theory

Abstract

Spin-phonon coupling is the main drive of spin relaxation and decoherence in solidstate semiconductors at finite temperature. Controlling this interaction is a central problem for many disciplines, ranging from magnetic resonance to quantum technologies. Spin relaxation theories have been developed for almost a century but often employ a phenomenological description of phonons and their coupling to spin, resulting in a non-predictive tool and hindering our detailed understanding of spin dynamics.Here we combine fourth-order time-local quantum master equations with advanced electronic structure methods and perform predictions of spin-phonon relaxation time for a series of solid-state coordination compounds based on both transition metals and lanthanide Kramers ions. The agreement between experiments and simulations demonstrates that an accurate, universal and fully ab initio implementation of spin relaxation theory is possible, thus paving the way to a systematic study of spin-phonon relaxation in solid-state materials.

Spin-Phonon Relaxation in Magnetic Molecules: Theory, Predictions and Insights

“…119 have been derived in the present form in Ref. [58] and that it differs from the one previously proposed in ref. [57].…”

“…This is due to the fact that in the opposite regime, dipolar spin-spin coupling, not included in the simulations, becomes the dominant source of relaxation. Indeed, when diluted samples are measured with EPR inversion recovery, a much better agreement is observed [58].…”

“…37 was obtained by truncating the expansion of ρ to the second order in , but higher order terms might in principle contribute to the dynamics of the density matrix. In this section we will explore the role of the next perturbative order [57,58]. Iterating the procedure used to derive Eq.…”

“…However, in the presence of degenerate states, this separation is no longer justified and the dynamics of the entire density matrix must be studied. [58]…”

“…As discussed in Ref. [58], this is almost entirely due to the misuse of the secular approximation, which does not totally decouple coherence and population terms of the density matrix for Kramers systems in zero external field. Once the secular approximation is correctly carried out, the agreement between experiments and theory becomes virtually exact [58].…”