Frustrated ferromagnetic spin-1/2 chain in a magnetic field: The phase diagram and thermodynamic properties

TL;DR

This paper investigates the phase diagram and thermodynamic properties of a frustrated ferromagnetic spin-1/2 chain in a magnetic field using theoretical and numerical methods, revealing a novel EO phase and specific heat features.

Contribution

It introduces the 'even-odd' phase in the phase diagram and combines multiple methods to analyze thermodynamic behavior in frustrated chains.

Findings

Identification of the 'even-odd' phase with magnon pairs

First-order transition indicated by magnetization jump

Double-peak structure in specific heat at zero field

Abstract

The frustrated ferromagnetic spin-1/2 Heisenberg chain is studied by means of a low-energy field theory as well as the density-matrix renormalization group and exact diagonalization methods. Firstly, we study the ground-state phase diagram in a magnetic field and find an `even-odd' (EO) phase characterized by bound pairs of magnons in the region of two weakly coupled antiferromagnetic chains. A jump in the magnetization curves signals a first-order transition at the boundary of the EO phase, but otherwise the curves are smooth. Secondly, we discuss thermodynamic properties at zero field, where we confirm a double-peak structure in the specific heat for moderate frustrating next-nearest neighbor interactions.