Localization effects due to a random magnetic field on heat transport in a harmonic chain

TL;DR

This paper investigates how a disordered magnetic field affects heat transport in a harmonic chain, revealing that low-frequency modes dominate conduction and that the magnetic field's average influences the power-law decay of heat current with system size.

Contribution

It provides a detailed analysis of the localization effects and heat transport behavior in a harmonic chain under random magnetic fields, highlighting the dependence on the magnetic field's average and boundary conditions.

Findings

Localization length diverges at zero frequency

Heat current decays as a power law with system size

Different power laws arise depending on magnetic field average and boundary conditions

Abstract

We consider a harmonic chain of $N$ oscillators in presence of a disordered magnetic field. The ends of the chain are connected to heat baths and we study the effects of the magnetic field randomness on the heat transport. The disorder, in general, causes localization of the normal modes due to which a system becomes insulating. However, for this system, the localization length diverges as the normal mode frequency approaches zero. Therefore, the low frequency modes contribute to the transmission, $\mathcal{T}_N(\omega)$, and the heat current goes down as a power law with the system size, $N$. This power law is determined by the small frequency behaviour of some Lyapunov exponent, $\lambda(\omega)$, and the transmission in the thermodynamic limit, $\mathcal{T}_\infty(\omega)$. While it is known that in the presence of a constant magnetic field $\mathcal{T}_\infty(\omega)\sim \omega^{3/2},~ \omega^{1/2}$ depending on the boundary conditions, we find that the Lyapunov exponent for the system behaves as $\lambda(\omega)\sim\omega$ for $\expval{B}\neq 0$ and $\lambda(\omega)\sim\omega^{2/3}$ for $\expval{B}=0$. Therefore, we obtain different power laws for current vs $N$ depending on $\expval{B}$ and the boundary conditions.