Observation of Giant Spin Splitting and d-wave Spin Texture in Room Temperature Altermagnet RuO2

Abstract Recently, a new magnetic phase called altermagnetism has been proposed, ushering in a third distinct magnetic phase beyond ferromagnetism and antiferromagnetism. It is expected that this groundbreaking phase exhibits unique physical properties such as C-paired spin-valley locking, anomalous Hall effect, nontrivial Berry phase, and giant magnetoresistance. Among all the predicted candidates, several room temperature altermagnets are suggested to host significant potential applications. Nevertheless, direct evidence about the spin pattern of the room temperature altermagnet is still unrevealed. RuO2 is identified as the most promising candidate for room temperature d-wave altermagnetism exhibiting a substantial spin splitting of up to 1.4 eV in previous research. In this study, utilizing angle-resolved photoemission spectroscopy (ARPES), we report experimental observation of the giant spin splitting in RuO2. Furthermore, employing spin-ARPES, we directly observed the d-wave spin pattern. Our results unequivocally show that RuO2 is a perfect d-wave altermagnet with great potential for upcoming spintronic applications.