Thermally induced spin emergent effect on ultrafast spin dynamics in Ni₄

It has already been shown that coupling of spins to an external heat bath can lead to interesting spin dynamics, e.g., the Spin Seebeck [1] and the Nernst effect. Here, using state-of-the-art ab initio quantum chemical calculations we present a new spin emergent effect, in which the combination of a laser pulse and a thermal bath gives rise to a transient spin-flip scenario [2] on a structurally distorted Ni₄, not possible otherwise.

The thermal coupling is described using the Lindblad-superoperator formalism. Furthermore, the Fourier analysis of the resulting spin and charge relaxation reveals two different regimes. We compare the time regimes of charge and spin and discuss the origin of their differences. Additionally, we investigate the effects of using two thermal baths on a model system [3]. It turns out that for an asymmetric coupling the population of the ground state triplet can be inverted with respect to the thermally equilibrated ones, thus the magnetization changes sign. Finally, we find that the Lamb-shift creates fluctuations in the spin values.

[1] G. Lefkidis and S. A. Reyes, Phys. Rev. B 94, 1444333 (2016)
[2] C. Li, J. Liu, S. Zhang, G. Lefkidis, and W. Hübner, Carbon 87, 153 (2015)
[3] G. Lefkidis, S. Sold, and W. Hübner, J. Magn. Magn. Mater. 432, 276 (2017)