Spin-orbit-driven quarter semimetals in rhombohedral graphene

TL;DR

This paper reports the discovery of spin-orbit-driven quarter semimetals in rhombohedral multilayer graphene, revealing novel topological and correlated phenomena such as spontaneous symmetry breaking and phase transitions to Chern insulators.

Contribution

It demonstrates the emergence of quarter semimetals in rhombohedral graphene with spin-orbit coupling, highlighting new topological states and correlation effects.

Findings

Observation of nearly vanished Hall resistance and parabolic longitudinal resistance.

Detection of spontaneous time-reversal symmetry breaking via anomalous Hall effect.

Magnetic field-induced transition from quarter semimetals to Chern insulators.

Abstract

Semimetals exhibit intriguing characteristics attributed to the coexistence of both electrons and holes. In rhombohedral multilayer graphene, a strong trigonal warping effect gives rise to a semi-metallic state near the Fermi surface, offering unique opportunities to explore the interplay of semi-metallic properties with strong correlations and topologies. Here, the observation of quarter semimetals in rhombohedral multilayer graphene by introducing spin-orbit coupling (SOC) is reported. The semi-metallic characteristics of rhombohedral graphene manifest as nearly vanished Hall resistance and parabolic longitudinal resistance. The strong correlations arising from the surface flat band lead to spontaneous symmetry breaking. SOC proximitized by WSe2 further lifts the valley degeneracy, resulting in the spontaneous time-reversal symmetry breaking, as evidenced by the hysteretic anomalous Hall effect. The coexistence of fully polarized electrons and holes allows for the observation of a non-monotonic temperature dependence of the anomalous Hall resistance. Furthermore, the application of moderate magnetic fields induces a phase transition from quarter semimetals to Chern insulators. These findings establish rhombohedral multilayer graphene as an ideal platform for studying strong correlations and topologies in semimetals.