Transport across junctions of altermagnets with normal metals and ferromagnets.

Altermagnet (AM) is a novel time reversal symmetry broken magnetic phase with $d$-wave order which has been experimentally realized recently. We discuss theoretical models of altermagnet based systems on lattice and in continuum. We show equivalence between the lattice and continuum models by mapping the respective parameters. We study (i) altermagnet-normal metal (NM) and (ii) altermagnet-ferromagnet (FM) junctions, with the aim to quantify transport properties such as conductivity and magnetoresistance. We find that a spin current accompanies charge current when a bias is applied. The magnetoresistance of AM-FM junction switches sign when AM is rotated by $90^{\circ}$ -- a feature unique to the altermagnetic phase.