Thermodynamics of the frustrated ferromagnetic spin-1/2 Heisenberg chain

TL;DR

This paper investigates the thermodynamic properties of a frustrated ferromagnetic spin-1/2 Heisenberg chain, revealing how frustration affects susceptibility and specific heat near quantum criticality.

Contribution

It provides a detailed analysis of thermodynamic behavior in the J1-J2 chain, highlighting the impact of frustration on critical indices and low-temperature properties.

Findings

Susceptibility changes from T^{-2} to T^{-3/2} at the critical point.

An extra low-temperature maximum in specific heat appears due to frustration.

Critical indices remain unchanged by frustration within the ferromagnetic ground state.

Abstract

We studied the thermodynamics of the one-dimensional J1-J2 spin-1/2 Heisenberg chain for ferromagnetic nearest-neighbor bonds J1 < 0 and frustrating antiferromagnetic next-nearest-neighbor bonds J1 > 0 using full diagonalization of finite rings and a second-order Green-function formalism. Thereby we focus on J2 < |J1|/4 where the ground state is still ferromagnetic, but the frustration influences the thermodynamic properties. We found that their critical indices are not changed by J2. The analysis of the low-temperature behavior of the susceptibility chi leads to the conclusion that this behavior changes from chi \propto T^{-2} at J2 < |J1|/4 to chi \propto T^{-3/2} at the quantum-critical point J2=|J1|/4. Another effect of the frustration is the appearance of an extra low-T maximum in the specific heat C_v(T) for J2 \gtrsim |J1|/8, indicating its strong influence on the low-energy spectrum.