Weak-coupling altermagnetism and chiral magnetic excitations in a checkerboard lattice

Abstract

Altermagnets, characterized by spin-split electronic bands with compensated magnetic moments, have emerged as a new class of magnetic materials garnering attention in recent years. Here, using a minimal one-band Hubbard model, we show that the checkerboard lattice serves as a natural platform for altermagnetism for electrons. The instability towards altermagnetic order is denoted by diverging altermagnetic susceptibility at weak-coupling. Carrying out mean-field treatment of the Hubbard repulsion, we show phase transitions from the nonmagnetic to altermagnetic semimetal and then to altermagnetic insulating phase, allowing clear identification of spin-split states. We then examine magnetic excitations in the altermagnetic phases using a random-phase approximation treatment of the dynamical spin susceptibility. The altermagnetic order is found to be stable against spin-fluctuations with the excitation spectra showing well-defined magnon excitations, which decay into single-particle excitations with decreasing interaction strength. Remarkably, the magnetic excitations exhibit strong dependence on both chirality and direction, showing an alternating chirality splitting, similar to the alternating spin splitting of the electronic bands, which serves as a salient feature of altermagnetism.