Phase diagrams and universality classes of random antiferromagnetic spin ladders

TL;DR

This paper explores the phase diagrams and universality classes of random antiferromagnetic spin ladders, revealing their relation to known classes and identifying a new fixed point at intermediate disorder.

Contribution

It provides a comprehensive analysis of phase diagrams for random spin ladders and identifies a new universal fixed point at intermediate disorder levels.

Findings

The two-leg ladder belongs to the same universality class as the dimerized random spin-1/2 chain.

The zigzag ladder exhibits a random singlet phase at weak disorder and frustration.

A new universal fixed point is discovered at intermediate disorder.

Abstract

The random antiferromagnetic two-leg and zigzag spin-1/2 ladders are investigated using the real space renormalization group scheme and their complete phase diagrams are determined. We demonstrate that the first system belongs to the same universality class of the dimerized random spin-1/2 chain. The zigzag ladder, on the other hand, is in a random singlet phase at weak frustration and disorder. Otherwise, we give additional evidence that it belongs to the universality class of the random antiferromagnetic and ferromagnetic quantum spin chains, although the universal fixed point found in the latter system is never realized. We find, however, a new universal fixed point at intermediate disorder.