Local signatures of altermagnetism

TL;DR

This paper investigates local electronic signatures of altermagnetism near impurities, revealing how their unique spin-split band structures produce measurable local density of states patterns, especially in the presence of coexisting superconductivity.

Contribution

It provides a comprehensive classification of two-dimensional altermagnetic models and predicts impurity-induced local density of states signatures detectable by scanning tunneling microscopy.

Findings

Local density of states reflects the momentum-space node structure.

Impurity responses are enhanced in coexistence with superconductivity.

Sublattice degrees of freedom are crucial for modeling altermagnetism.

Abstract

Altermagnets constitute a class of collinear compensated N\'eel ordered magnets that break time-reversal symmetry and feature spin-split band structures. Based on versatile microscopic models able to capture the altermagnetic sublattice degrees of freedom, we study characteristic local signatures of altermagnetism near disorder sites. We give a complete list of two-dimensional models that exhibit altermagnetism classified by their corresponding layer groups. Specifically, we calculate the local density of states in the vicinity of pointlike nonmagnetic impurities and expose its spatial dependence for two minimal models showcasing $d$-wave and $g$-wave altermagnetism. The momentum structure of the nodes ($d$-wave, $g$-wave, etc.) is directly imprinted on the total local density of states, thus measurable by scanning tunneling conductance experiments. This signature is present both in the spin-resolved as well as the spin-summed local density of states. We find a weaker response in the nonmagnetic state from the anisotropic crystal environment and uncover the importance of the sublattice degree of freedom to model altermagnets. We also study coexistence phases of altermagnetism and superconductivity and provide predictions for the local impurity response of in-gap bound states. The response of impurity bound states strongly enhances the distinct altermagnetic signature.