Anisotropic signatures in the spin–boson model

Abstract

Thermal equilibrium properties of nanoscale systems deviate from standard macroscopic predictions due to non–negligible coupling to the environment. For anisotropic three–dimensional materials, we derive the mean force corrections to the equilibrium state of a classical spin vector. Specifically, we consider cubic, orthorhombic, and monoclinic symmetries, and compare their spin expectation values as a function of temperature. The results are valid at arbitrary coupling strength. We underpin the correctness of the mean force state by evidencing its match with the steady state of the simulated non–Markovian spin dynamics. The results show an explicit dependence on the symmetry of the confining material. In addition, some coupling symmetries show a spin alignment transition at zero temperature. Finally, we quantify the work extraction potential of the mean force–generated inhomogeneities in the energy shells. Such inhomogeneities constitute a classical equivalent to quantum coherences.