Spin-valley coupling in single-electron bilayer graphene quantum dots

TL;DR

This paper reports the observation of spin-valley coupling in a single-electron bilayer graphene quantum dot, revealing a Kane-Mele type spin-orbit interaction and setting limits on disorder-induced mixing, advancing quantum dot spin-valley physics.

Contribution

It demonstrates the experimental detection of spin-valley coupling in bilayer graphene quantum dots with high energy resolution, a key step for spin-valley qubit development.

Findings

Resolved fourfold spin and valley degeneracy lifting

Measured Kane-Mele type spin-orbit coupling of ~65 μeV

Set upper limit of disorder-induced K-K' mixing below 20 μeV

Abstract

Understanding how the electron spin is coupled to orbital degrees of freedom, such as a valley degree of freedom in solid-state systems is central to applications in spin-based electronics and quantum computation. Recent developments in the preparation of electrostatically-confined quantum dots in gapped bilayer graphene (BLG) enables to study the low-energy single-electron spectra in BLG quantum dots, which is crucial for potential spin and spin-valley qubit operations. Here, we present the observation of the spin-valley coupling in a bilayer graphene quantum dot in the single-electron regime. By making use of a highly-tunable double quantum dot device we achieve an energy resolution allowing us to resolve the lifting of the fourfold spin and valley degeneracy by a Kane-Mele type spin-orbit coupling of $\approx 65~\mu$eV. Also, we find an upper limit of a potentially disorder-induced mixing of the $K$ and $K'$ states below $20~\mu$eV.