Heat current magnification in Classical and Quantum spin networks

TL;DR

This paper explores heat current magnification in classical and quantum spin networks, demonstrating how asymmetry in spin interactions and system parameters can induce and control current magnification phenomena.

Contribution

It introduces new mechanisms for heat current magnification using asymmetry in spin interaction strengths and energy levels, supported by classical and quantum models.

Findings

Current magnification requires specific asymmetries in spin interactions.

Magnification is associated with a dip in total current due to energy level intersections.

Magnification occurs when temperature gradient and interaction strength are comparable.

Abstract

We investigate heat current magnification due to asymmetry in the number of spins in two-branched classical and quantum spin systems. We begin by studying the classical Ising like spin models using Q2R and CCA dynamics and show that just the difference in the number of spins is not enough and some other source of asymmetry is required to observe heat current magnification. Unequal spin--spin interaction strength in the upper and lower branch is employed as a source of this asymmetry and it proves adequate for generating current magnification in both the models. Suitable physical motivation is then provided for current magnification in these systems, along with ways to control and manipulate magnification through various system parameters. We also study a five spin Quantum system with modified Heisenberg XXZ interaction and preserved magnetisation using the Redfield master equation. We show that it is possible to generate current magnification in this model by the asymmetry in the number of spins only. Our results indicate that the onset of current magnification is accompanied by a dip in the total current flowing through the system. On analysis it is revealed that this dip might occur because of the intersection of two non-degenerate energy levels for certain values of the asymmetry parameter in the modified XXZ model. We deduce that the additional degeneracy and the ergodic constraint due to fixed magnetisation in the system are the main reasons for current magnification and other atypical behaviors observed. We then use the concept of `ergotropy' to support these findings. Finally, for both the classical and quantum models, we see that current magnification is only observed when temperature gradient and intra-system interaction strength have similar order of energy.