Finite size scaling in Ising-like systems with quenched random fields: Evidence of hyperscaling violation

TL;DR

This paper investigates how modified hyperscaling relations affect finite size scaling in random field Ising systems, revealing non-universal interface free energy scaling and proposing new numerical methods for critical point detection.

Contribution

It demonstrates the breakdown of standard hyperscaling in random field systems and introduces a power-law scaling of interface free energy, enabling improved critical point identification.

Findings

Interface free energy scales as L^θ at criticality

Modified hyperscaling relation replaces standard form

New numerical methods successfully locate critical points

Abstract

In systems belonging to the universality class of the random field Ising model, the standard hyperscaling relation between critical exponents does not hold, but is replaced by a modified hyperscaling relation. As a result, standard formulations of finite size scaling near critical points break down. In this work, the consequences of modified hyperscaling are analyzed in detail. The most striking outcome is that the free energy cost \Delta F of interface formation at the critical point is no longer a universal constant, but instead increases as a power law with system size, \Delta F proportional to $L^\theta$, with $\theta$ the violation of hyperscaling critical exponent, and L the linear extension of the system. This modified behavior facilitates a number of new numerical approaches that can be used to locate critical points in random field systems from finite size simulation data. We test and confirm the new approaches on two random field systems in three dimensions, namely the random field Ising model, and the demixing transition in the Widom-Rowlinson fluid with quenched obstacles.