Physical review. B, Solid state
Bounded and inhomogeneous Ising models. II. Specific-heat scaling function for a strip
Helen Au-Yang, Michael Ellis Fisher
Abstract
The specific heat, energy, and free energy of an infinitely long, square-lattice ferromagnetic Ising strip consisting of $n$ parallel layers with free boundary conditions and a surface magnetic field ${H}_{1}={k}_{B}{\mathrm{Th}}_{1}$ imposed on the last layer, is analyzed for large $n$ in the light of finite-size scaling theory. It is shown rigorously that the free energy (and, similarly, the energy and specific heat) can be written asymptotically in the scaling form $\ensuremath{\Delta}f(n,t,{h}_{1})\ensuremath{\approx}{n}^{\ensuremath{-}2}(\mathrm{ln}n){W}_{1}(nt,{n}^{\frac{1}{2}}{h}_{1})+{n}^{\ensuremath{-}2}{W}_{2}(nt,{n}^{\frac{1}{2}}{h}_{1})$, where $t=\frac{(T\ensuremath{-}{T}_{c})}{{T}_{c}}$. The scaling functions ${W}_{i}(x,y)$ are computed in explicit closed form and shown to verify all the analyticity and asymptotic requirements anticipated by scaling theory. Furthermore, in the limit $n\ensuremath{\rightarrow}\ensuremath{\infty}$ at fixed $t\ensuremath{\ne}0$, the bulk and surface contributions to the thermodynamic properties are found to account for all except a correction of order ${e}^{\frac{\mathrm{pna}}{\ensuremath{\xi}(T)}}$, where $a$ is the lattice spacing and $\ensuremath{\xi}(T)$ is the bulk correlation length; the value of the small rational constant $p$ is interpreted in terms of interference effects between the two opposite boundaries (or "surfaces").