Weyl-Transition-Driven Giant Reversible Orbital Hall Conductivity

TL;DR

This paper uncovers a mechanism where tilted Weyl crossings in orbitally distinct bands create asymmetric orbital Berry curvature, enabling giant and reversible orbital Hall conductivity in monolayer PtBi2 through strain-induced Weyl transitions.

Contribution

It introduces a general Weyl-transition mechanism for controlling orbital Hall conductivity, demonstrated via first-principles calculations on monolayer PtBi2.

Findings

Giant orbital Hall conductivity driven by Weyl points.

Reversible sign change of OHC via strain-induced Weyl transitions.

Strain-induced structural phase transition influences OHC control.

Abstract

Orbital Hall conductivity (OHC) is a central ingredient of orbitronics, yet how to control it microscopically remains largely unexplored. Here we identify a general mechanism in which tilted Weyl crossings formed by orbitally distinct bands generate a strongly asymmetric orbital Berry curvature (OBC) distribution, whose imbalance survives Brillouin-zone integration and yields a sizable OHC already at zeroth order. Using first-principles calculations, we show that monolayer PtBi2 realizes this mechanism and hosts a giant OHC dominated by a type-II Weyl point. A small biaxial tensile strain drives a type-II $\rightarrow$ type-I $\rightarrow$ type-II Weyl transition, leading to a reversible sign change of the OHC through the evolution of the OBC imbalance. This process is governed by the chiral orbital texture of the crossing bands and is further assisted by a strain-induced first-order structural phase transition through bonding reconstruction and polarization change. Our results establish Weyl engineering of orbital quantum geometry as a powerful route to generating and reversibly controlling OHC in polar multi-orbital materials.