The Structure of Physical Crystalline Membranes within the Self-Consistent Screening Approximation

TL;DR

This paper calculates the critical exponents of crystalline membranes using a self-consistent screening approximation, extending previous work and demonstrating the method's accuracy and relevance to experiments.

Contribution

It extends the SCSA method to second order in 1/d_C for crystalline membranes, providing more accurate critical exponents and validating the approach's effectiveness.

Findings

The bending rigidity exponent eta=0.789

The elasticity softening exponent eta_u=0.422

The roughness exponent zeta=0.605

Abstract

The anomalous exponents governing the long wavelength behavior of the flat phase of physical crystalline membranes are calculated within a self-consistent screening approximation (SCSA) applied to second order expansion in 1/d_C (d_C is the co-dimension), extending the seminal work of Le Doussal and Radzihovsky [Phys. Rev. Lett. 69, 1209 (1992)]. In particular, the bending rigidity is found to harden algebraically in the long wavelength limit with an exponent eta=0.789..., which is used to extract the elasticity softening exponent eta_u=0.422..., and the roughness exponent zeta=0.605.... The scaling relation eta_u=2-2eta is proven to hold to all orders in SCSA. Further, applying the SCSA to an expansion in 1/d_C, is found to be essential, as no solution to the self-consistent equations is found in a two bubble level, which is the naive second order expansion. Surprisingly, even though the expansion parameter for physical membrane is 1/d_C=1, the SCSA applied to second order expansion deviates only slightly from the first order, increasing zeta by mere 0.016. This supports the high quality of the SCSA for physical crystalline membranes, as well as improves the comparison to experiments and numerical simulations of these systems. The prediction of SCSA applied to first order expansion for the Poisson ratio is shown to be exact to all orders.