One-directional polarization transport in electron/nuclear spin chains with loss and gain

TL;DR

This paper explores how non-Hermitian dynamics in electron/nuclear spin chains can be controlled to produce site-dependent polarization and robust spin currents, with potential applications in magnetic resonance technologies.

Contribution

It introduces a theoretical framework for manipulating spin polarization flow in chains with loss and gain, revealing new polarization patterns and robustness mechanisms.

Findings

Adjusting electron spin pumping controls nuclear polarization distribution.

Ring-like patterns support non-decaying nuclear spin currents.

Cyclic magnetic field modulation enhances robustness to defects.

Abstract

Understanding the joint dynamics of electron and nuclear spins is central to core concepts in solid-state magnetic resonance - such as spin-lattice relaxation and dynamic nuclear polarization - but a generalization that capitalizes on competing polarization loss and gain channels is still lacking. Here, we theoretically study the non-Hermitian dynamics of hybrid electron/nuclear spin systems in the simultaneous presence of electron spin pumping and spin-lattice relaxation. Focusing on periodic, one-dimensional chains, we find that by adjusting the electron spin pumping to a critical level, it is possible to steer the flow of nuclear polarization to create site-dependent distributions where either end of the array polarizes in opposite ways, irrespective of the initial state. By contrast, we show that ring-like patterns - where the limit nuclear polarization is uniform - exhibit a non-decaying, externally-driven nuclear spin current. Interestingly, cyclic magnetic field modulation can render these processes largely robust to defects in the chain, a response featuring some interesting similarities - and differences - with recent findings in other non-Hermitian physical platforms.