Low Energy Properties of the Random Spin-1/2 Ferromagnetic-Antiferromagnetic Heisenberg Chain

TL;DR

This study investigates the low energy behavior of a disordered spin-1/2 Heisenberg chain with mixed ferromagnetic and antiferromagnetic interactions using DMRG and RSRG methods, revealing deviations from the random singlet phase and effects on thermodynamic properties.

Contribution

It provides a comparative analysis of DMRG and RSRG methods on the disordered chain and characterizes the crossover from large-spin states to the random singlet phase.

Findings

Deviation of gap distribution from the random singlet phase

Formation of large-spin states even in small systems

Crossover effects on susceptibility and specific heat

Abstract

The low energy properties of the spin-1/2 random Heisenberg chain with ferromagnetic and antiferromagnetic interactions are studied by means of the density matrix renormalization group (DMRG) and real space renormalization group (RSRG) method for finite chains. The results of the two methods are consistent with each other. The deviation of the gap distribution from that of the random singlet phase and the formation of the large-spin state is observed even for relatively small systems. For a small fraction of the ferromagnetic bond, the effect of the crossover to the random singlet phase on the low temperature susceptibility and specific heat is discussed. The crossover concentration of the ferromagnetic bond is estimated from the numerical data.