Counterintuitive gate dependence of weak antilocalization in bilayer graphene/WSe$_2$ heterostructures

TL;DR

This study reveals that weak antilocalization in bilayer graphene/WSe$_2$ heterostructures exhibits a maximum at zero electric displacement field, contrary to expectations, due to complex spin lifetime dependencies.

Contribution

The paper uncovers the counterintuitive gate dependence of WAL in BLG/TMDC heterostructures, supported by experimental data and theoretical modeling of spin dynamics.

Findings

WAL visibility peaks at zero displacement field.

Counterintuitive WAL behavior explained by spin lifetime dependencies.

Theoretical calculations confirm experimental observations.

Abstract

Strong gate control of proximity-induced spin-orbit coupling was recently predicted in bilayer graphene/transition metal dichalcogenides (BLG/TMDC) heterostructures, as charge carriers can easily be shifted between the two graphene layers, and only one of them is in close contact to the TMDC. The presence of spin-orbit coupling can be probed by weak antilocalization (WAL) in low field magnetotransport measurements. When the spin-orbit splitting in such a heterostructure increases with the out of plane electric displacement field $\bar D$, one intuitively expects a concomitant increase of WAL visibility. Our experiments show that this is not the case. Instead, we observe a maximum of WAL visibility around $\bar D=0$. This counterintuitive behaviour originates in the intricate dependence of WAL in graphene on symmetric and antisymmetric spin lifetimes, caused by the valley-Zeeman and Rashba terms, respectively. Our observations are confirmed by calculating spin precession and spin lifetimes from an $8\times 8$ model Hamiltonian of BLG/TMDC.