Observation of the spin-orbit gap in bilayer graphene by one-dimensional ballistic transport

TL;DR

This study demonstrates tunable spin-orbit induced subband splittings in bilayer graphene via quantum point contacts, revealing complex magnetic field effects and spin-polarized transport, advancing understanding of spin-orbit interactions in 2D materials.

Contribution

First observation of gate-tunable spin-orbit gap in bilayer graphene using ballistic transport measurements, highlighting proximity effects and complex magnetic field behaviors.

Findings

Subband splitting tunable from 40 to 80 μeV by displacement field

Detection of a spin-polarized 6 e^2/h channel at high magnetic field

Observation of interaction effects at spin-split subband crossings

Abstract

We report on measurements of quantized conductance in gate-defined quantum point contacts in bilayer graphene that allow the observation of subband splittings due to spin-orbit coupling. The size of this splitting can be tuned from 40 to 80 $\mu$eV by the displacement field. We assign this gate-tunable subband-splitting to a gap induced by spin-orbit coupling of Kane-Mele type, enhanced by proximity effects due to the substrate. We show that this spin-orbit coupling gives rise to a complex pattern in low perpendicular magnetic fields, increasing the Zeeman splitting in one valley and suppressing it in the other one. In addition, we observe the existence of a spin-polarized channel of 6 e$^2$/h at high in-plane magnetic field and of signatures of interaction effects at the crossings of spin-split subbands of opposite spins at finite magnetic field.