Nambu monopoles interacting with lattice defects in two-dimensional artificial square spin ice

TL;DR

This paper investigates how Nambu monopoles in two-dimensional artificial square spin ice interact with lattice defects, revealing that defects act like magnetic charges and influence monopole interactions through a rapidly decaying string effect.

Contribution

It introduces a model describing the interaction between Nambu monopoles and lattice defects as involving four magnetic charges and a string, with detailed analysis of defect influence.

Findings

Defects behave as magnetic charges with opposite poles.

The interaction involves four magnetic charges and a string.

String influence diminishes quickly with distance.

Abstract

The interactions between an excitation (similar to a pair of Nambu monopoles) and a lattice defect are studied in an artificial two-dimensional square spin ice. This is done by considering a square array of islands containing only one island different from all others. This difference is incorporated in the magnetic moment (spin) of the "imperfect" island and several cases are studied, including the special situation in which this distinct spin is zero (vacancy). We have shown that the two extreme points of a malformed island behave like two opposite magnetic charges. Then, the effective interaction between a pair of Nambu monopoles with the deformed island is a problem involving four magnetic charges (two pairs of opposite poles) and a string. We also sketch the configuration of the field lines of these four charges to confirm this picture. The influence of the string on this interaction decays rapidly with the string distance from the defect.