Unusual interlayer quantum transport behavior caused by the zeroth Landau level in YbMnBi2

TL;DR

This study reveals unique quantum transport phenomena caused by the zeroth Landau level in YbMnBi2, a topological semimetal with linear band crossings, highlighting the effects of relativistic fermions on magnetoresistance and Hall resistivity.

Contribution

It provides the first experimental observation of the zeroth Landau level's impact on transport in a multiband topological semimetal with crossings at and away from the Fermi level.

Findings

Observation of Shubnikov de-Haas oscillations linked to Dirac bands above or below Fermi level.

Unusual angular dependence of out-of-plane magnetoresistance and Hall resistivity.

Evidence of the zeroth Landau level's degeneracy dependence on magnetic field orientation.

Abstract

Relativistic fermions in topological quantum materials are characterized by linear energy-momentum dispersion near band crossing points. Under magnetic field, relativistic fermions acquire Berry phase of {\pi} in cyclotron motion, leading to a zeroth Landau level (LL) at the crossing point. Such field-independent zeroth LL, which distinguishes relativistic fermions from conventional electron systems, is hardly probed in transport measurements since the Fermi energy (EF) is usually not right at the band crossing points in most topological materials. Here we report the observation of exotic quantum transport behavior resulting from the zeroth LL in a multiband topological semimetal YbMnBi2 which possesses linear band crossings both at and away from the Fermi level (FL). We show that the Dirac bands with the crossing points being above or below the FL leads to Shubnikov de-Haas oscillations in the in-plane magnetoresistance, whereas the Dirac bands with the crossing points being at the FL results in unusual angular dependences of the out-of-plane magnetoresistance and in-plane Hall resistivity due to the dependence of the zeroth LL's degeneracy on field orientation. Our results shed light on the transport mechanism of the zeroth LL's relativistic fermions in layered materials.