Condensed Matter Seminar Series

Luca Banszerus

RWTH Aachen University

Gate-defined quantum dots in bilayer graphene

Bilayer graphene (BLG) quantum dots (QDs) have long been regarded as an attractive platform for hosting spin qubits since the low nuclear spin densities and weak spin-orbit interaction in BLG promise long spin coherence times. In addition to the spin, BLG exhibits a tunable valley degree of freedom, which is associated with a strong out-of-plane magnetic moment with opposite signs for the K- and K'-valley. This allows controlling the valley splitting in BLG and to use valley space as an additional qubit platform.  

In contrast to conventional semiconductors, the band structure of BLG is (almost) perfectly electron/hole symmetric  and exhibits a small, electrically tunable band gap, which allows forming ambipolar electron/hole double QDs.

In my talk, I will present electrostatically confined BLG single and double QDs based on ultraclean van-der-Waals heterostructures. By making use of the high energy resolution of the interdot transitions in a single electron double QD, we reconstruct the single particle spectrum of BLG and resolve the lifting of the fourfold spin and valley degeneracy of the single-particle spectrum by a Kane-Mele type spin-orbit coupling gap of 65µeV.

Next, I will present magnetospectroscopy data of a single electron/single hole ambipolar double QD, where interdot tunneling processes can be described by the creation and annihilation of single electron-hole pairs with opposite quantum numbers. Interestingly, the electron-hole symmetry results in a protected single particle Pauli blockade, which allows for spin-to-charge and valley-to-charge conversion, which is essential for the readout of spin and valley qubits.

During the last part of my talk, I will present transient current spectroscopy experiments which allow measuring the spin T1 times in a single electron quantum dot.