Spin-lattice relaxation theory has been developed over almost a century, but some cardinal assumptions on the nature of the interactions involved have never been fully verified. This includes the weak coupling approximation, which makes it possible to describe spin dynamics perturbatively and leads to the canonical description of spin relaxation in terms of one- and two-phonon processes. Here, we extend the first-principles theory of spin relaxation to three-phonon processes and apply it to the vdW crystal of a spin-1/2 Chromium nitride complex. Results show that three-phonon contributions to spin relaxation only become relevant at temperatures inaccessible to experiments for this molecule, thus providing unprecedented evidence for the validity of the weak spin-phonon coupling assumption in spin relaxation theory. At the same time, we numerically show that a relatively small increase in spin-phonon coupling would lead to a crossover between three- and two-phonon processes' efficiency at room temperature, illustrating the possibility for three-phonon effects in molecular materials as well as paving the way to a systematic exploration of strong coupling in spin systems.Spin-lattice relaxation theory has been developed over almost a century, but some cardinal assumptions on the nature of the interactions involved have never been fully verified. This includes the weak coupling approximation, which makes it possible to describe spin dynamics perturbatively and leads to the canonical description of spin relaxation in terms of one- and two-phonon processes. Here, we extend the first-principles theory of spin relaxation to three-phonon processes and apply it to the vdW crystal of a spin-1/2 Chromium nitride complex. Results show that three-phonon contributions to spin relaxation only become relevant at temperatures inaccessible to experiments for this molecule, thus providing unprecedented evidence for the validity of the weak spin-phonon coupling assumption in spin relaxation theory. At the same time, we numerically show that a relatively small increase in spin-phonon coupling would lead to a crossover between three- and two-phonon processes' efficiency at room temperature, illustrating the possibility for three-phonon effects in molecular materials as well as paving the way to a systematic exploration of strong coupling in spin systems.

quant-pharXiv:2603.05393Mar 6, 2026

Relaxation in a one dimensional spin system

R. W. Gibberd, G.C. Stey

Physics Letters ASep 1, 19713 citations

Magnetic relaxation and He4 coverage in superfluid A13

Qiang Jiang, Haruo Kojima

Measurements on spin relaxation time in superfluid $^{3}\mathit{A}_{1}$ were carried out at a pressure of 22.4 bar and a static field of 7.5 kG. The influence of surface coverage by $^{4}\mathrm{He}$ was systematically explored. The $^{4}\mathrm{He}$ coverage is used to eliminate the spin relaxation at the boundary walls and to extract the spin relaxation time in the warmer half of bulk ${\mathit{A}}_{1}$ phase. The bulk spin relaxation time is much shorter than expected from Leggett-Takagi theory applied to the ${\mathit{A}}_{1}$ phase. In the colder half of the phase, $^{4}\mathrm{He}$ coverage anomalously has no effect on the spin relaxation time.Measurements on spin relaxation time in superfluid $^{3}\mathit{A}_{1}$ were carried out at a pressure of 22.4 bar and a static field of 7.5 kG. The influence of surface coverage by $^{4}\mathrm{He}$ was systematically explored. The $^{4}\mathrm{He}$ coverage is used to eliminate the spin relaxation at the boundary walls and to extract the spin relaxation time in the warmer half of bulk ${\mathit{A}}_{1}$ phase. The bulk spin relaxation time is much shorter than expected from Leggett-Takagi theory applied to the ${\mathit{A}}_{1}$ phase. In the colder half of the phase, $^{4}\mathrm{He}$ coverage anomalously has no effect on the spin relaxation time.

Physical review. B, Condensed matterJun 1, 19922 citations

Spin relaxation: is there anything new under the Sun?

Bogdan A. Rodin, Daniel Abergel

Spin relaxation has been at the core of many studies since the early days of nuclear magnetic resonance (NMR) and the underlying theory worked out by its founding fathers. This Bloch-Redfield-Abraham relaxation theory has been recently reinvestigated () in the perspective of Lindblad theory of quantum Markovian master equations in order to account for situations where the widely used semi-classical relaxation theory breaks down. In this article, we review the conventional approach of quantum mechanical theory of NMR relaxation and show that, under the usual assumptions, it is equivalent to the Lindblad formulation. We also comment on the debate on semi-classical versus quantum versions of spectral density functions involved in relaxation.Spin relaxation has been at the core of many studies since the early days of nuclear magnetic resonance (NMR) and the underlying theory worked out by its founding fathers. This Bloch-Redfield-Abraham relaxation theory has been recently reinvestigated () in the perspective of Lindblad theory of quantum Markovian master equations in order to account for situations where the widely used semi-classical relaxation theory breaks down. In this article, we review the conventional approach of quantum mechanical theory of NMR relaxation and show that, under the usual assumptions, it is equivalent to the Lindblad formulation. We also comment on the debate on semi-classical versus quantum versions of spectral density functions involved in relaxation.

Magnetic ResonanceFeb 9, 202212 citations

Measurements on spin relaxation time in superfluid

^{3}\mathit{A}_{1}

were carried out at a pressure of 22.4 bar and a static field of 7.5 kG. The influence of surface coverage by

^{4}\mathrm{He}

was systematically explored. The

^{4}\mathrm{He}

coverage is used to eliminate the spin relaxation at the boundary walls and to extract the spin relaxation time in the warmer half of bulk

{\mathit{A}}_{1}

phase. The bulk spin relaxation time is much shorter than expected from Leggett-Takagi theory applied to the

{\mathit{A}}_{1}

phase. In the colder half of the phase,

^{4}\mathrm{He}

coverage anomalously has no effect on the spin relaxation time.