Van Hove singularity-induced multiple magnetic transitions in multi-orbital systems

TL;DR

This paper demonstrates that Van Hove singularities in multi-orbital systems can induce various magnetic phase transitions, including intrinsic altermagnetism, by amplifying orbital-resolved spin fluctuations and stabilizing competing magnetic orders.

Contribution

It reveals that Van Hove singularities can stabilize multiple magnetic phases, including intrinsic altermagnetism, across all 2D Bravais lattices, highlighting a generic route to altermagnetism in correlated materials.

Findings

VHSs stabilize competing magnetic orders in multi-orbital systems.

Multiple magnetic phase transitions mapped via Hubbard-$U$-$J_H$ phase diagrams.

Intrinsic altermagnetism emerges from spontaneous orbital antiferromagnetism.

Abstract

Van Hove singularities (VHSs) amplify electronic correlations, providing a crucial platform for discovering novel quantum phase transitions. Here, we show that VHSs in multi-orbital systems can stabilize a variety of competing $\bm{Q}=0$ magnetic orders, including intrinsic altermagnetism emerging from spontaneous orbital antiferromagnetism. This intrinsic phase, in which antiparallel spins reside on distinct orbitals, is realized across all four 2D Bravais lattices. It is driven by orbital-resolved spin fluctuations enhanced by inter-orbital hopping and favors suppressed Hund's coupling $J_H$, strong inter-orbital hybridization, and filling near a VHS from quadratic band touching. Through Hubbard-$U$-$J_H$ phase diagrams we map several magnetic phase transitions: (i) ferrimagnet to $d$-wave extrinsic altermagnet, (ii) $d$-wave intrinsic altermagnet to ferromagnet, and (iii) $g$-wave extrinsic altermagnet to either $d$-wave extrinsic altermagnet or ferromagnet. Our work identifies VHSs as a generic route to altermagnetism in correlated materials.