diff --git a/docs/src/units.md b/docs/src/units.md index 6364768..32d13c8 100644 --- a/docs/src/units.md +++ b/docs/src/units.md @@ -78,8 +78,8 @@ parameters: - ``\bar{\alpha}``: amplitude of the Lorentzian spectral density. - ``\bar{T}``: the environment temperature. -These unit-free quantities are related to the unitful quantities in the previous -section by the following conversions: +These unit-free quantities (denoted hereon by a bar on top) are related to the +unitful quantities in the previous section by the following conversions: ```math \begin{align} \mathbf{B}_\mathrm{ext} &= B_0 \, \bar{B}_\mathrm{ext}, \\ @@ -93,8 +93,34 @@ T &= \frac{\hbar\omega_\mathrm{L}}{k_\mathrm{B}} \, \bar{T}. \end{align} ``` -With these definitions, the unit-free Gilbert damping is given by -(see [NJP 24 033020 (2022)](https://www.doi.org/10.1088/1367-2630/ac4ef2)) +Given these choices of rescaling and adimensionalisation and plugging them in +the equations of motion of the previous section, one finally gets the equations +being solved by SpiDy, that is +```math +\frac{\mathrm{d}\bar{\mathbf{S}}}{\mathrm{d}\bar{t}} = + \bar{\mathbf{S}}\times\left(\bar{\mathbf{B}}_\mathrm{ext} + \frac{1}{\sqrt{S_0}}\bar{\mathbf{b}} + \bar{\mathbf{V}}\right), \\ +\frac{\mathrm{d}\bar{\mathbf{V}}}{\mathrm{d}\bar{t}} = \bar{\mathbf{W}}, \\ +\frac{\mathrm{d}\bar{\mathbf{W}}}{\mathrm{d}\bar{t}} = \bar{\alpha}\bar{\mathbf{S}} - \bar{\omega}_0^2\bar{\mathbf{V}} - \bar{\Gamma}\bar{\mathbf{W}}, +``` +with environment Lorentzian spectral density +```math +\bar{J}(\bar{\omega}) = \frac{\bar{\alpha}\bar{\Gamma}}{\pi} \frac{\bar{\omega}}{(\bar{\omega}_0^2 - \bar{\omega}^2)^2 + \bar{\omega}^2\bar{\Gamma}^2}, +``` +and thermal stochastic noise $\bar{\mathbf{b}}$ with power spectral density +```math +\bar{P}(\bar{\omega}) = \pi \bar{J}(\bar{\omega})\bar{N}(\bar{\omega}). +``` +For the "quantum" noise, the noise term is given by +```math +\bar{N}_\mathrm{qu}(\bar{\omega}) = \coth\left(\frac{\bar{\omega}}{2\bar{T}}\right), +``` +while for "classical" noise we have +```math +\bar{N}_\mathrm{cl}(\bar{\omega}) = \frac{2\bar{T}}{\bar{\omega}}. +``` + +Finally, note that these definitions above, the unit-free Gilbert damping is +given by (see [NJP 24 033020 (2022)](https://www.doi.org/10.1088/1367-2630/ac4ef2)) ```math \eta = \frac{\bar{\alpha}\bar{\Gamma}}{\bar{\omega}_0^4}. ```