arXiv:2310.12801 · Physical review. B./Physical review. B
Roughness and critical force for depinning at 3-loop order
Mikhail N. Semeikin, Kay Jörg Wiese
Abstract
A $d$-dimensional elastic manifold at depinning is described by a renormalized field theory, based on the functional renormalization group (FRG). Here, we analyze this theory to 3-loop order, equivalent to third order in $\ensuremath{\epsilon}=4\ensuremath{-}d$, where $d$ is the internal dimension. The critical exponent reads $\ensuremath{\zeta}=\frac{\ensuremath{\epsilon}}{3}+0.04777{\ensuremath{\epsilon}}^{2}\ensuremath{-}0.068354{\ensuremath{\epsilon}}^{3}+O({\ensuremath{\epsilon}}^{4})$. Using that $\ensuremath{\zeta}(d=0)={2}^{\ensuremath{-}}$, we estimate $\ensuremath{\zeta}(d=1)=1.266(20)$, $\ensuremath{\zeta}(d=2)=0.752(1)$, and $\ensuremath{\zeta}(d=3)=0.357(1)$. For Gaussian disorder, the pinning force per site is estimated as ${f}_{\mathrm{c}}=\mathcal{B}{m}^{2}{\ensuremath{\rho}}_{m}+{f}_{\mathrm{c}}^{0}$, where ${m}^{2}$ is the strength of the confining potential, $\mathcal{B}$ a universal amplitude, ${\ensuremath{\rho}}_{m}$ the correlation length of the disorder, and ${f}_{\mathrm{c}}^{0}$ a nonuniversal lattice-dependent term. For charge-density waves, we find a mapping to the standard ${\ensuremath{\phi}}^{4}$ theory with $O(n)$ symmetry in the limit of $n\ensuremath{\rightarrow}\ensuremath{-}2$. This gives ${f}_{\mathrm{c}}=\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathcal{A}}(d){m}^{2}ln(m)+{f}_{\mathrm{c}}^{0}$, with $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\mathcal{A}}(d)=\ensuremath{-}{\ensuremath{\partial}}_{n}{[\ensuremath{\nu}{(d,n)}^{\ensuremath{-}1}+\ensuremath{\eta}(d,n)]}_{n=\ensuremath{-}2}$, reminiscent of logarithmic conformal field theories.