Flat-band ferromagnetism in the quasi-one-dimensional electride Y2Cl3 induced by hole doping

Abstract

Mielke and Tasaki's theoretical proposal of flatband ferromagnetism with the Hubbard model has attracted much attention due to the promising possibility of ferromagnetic order in electronic materials. Using first-principles density-functional theory calculations and tight-binding analysis, we present hole-doping-induced flatband ferromagnetism in the van der Waals layered insulating electride material ${\mathrm{Y}}_2{\mathrm{Cl}}_3$, whose structural framework consists of an array of weakly coupled one-dimensional (1D) Y wires. It is revealed that ${\mathrm{Y}}_2{\mathrm{Cl}}_3$, featuring a 1D paired, puckered diamond lattice of Y atoms, possesses three occupied valence states: the first- and second-highest ($S_1$ and $S_2$) states give rise to flatbands due to the destructive interference of Bloch wavefunctions, whereas the third-highest ($S_3$) state exhibits a dispersive band along the interstitial space within the paired diamond lattice. Upon partial hole doping of the $S_1$ band with a density larger than 0.3 holes per unit cell, we predict the emergence of ferromagnetism by satisfying the Stoner criterion, enabled by a high density of states at the Fermi level. Interestingly, the spin polarization of the $S_1$ band induces the nearly equal spin splitting of the $S_2$ and $S_3$ bands via the facilitated exchange interactions with the presence of interstitial anionic excess electrons. Our findings offer theoretical insights into an intricate flatband ferromagnetism in the experimentally synthesized 1D electride ${\mathrm{Y}}_2{\mathrm{Cl}}_3$ by hole doping, thereby enriching the family of 1D electride materials for spintronic applications.