2023

Linear-in-momentum spin orbit interactions in planar Ge/GeSi heterostructures and spin qubits
Esteban A. Rodríguez-Mena and José Carlos Abadillo-Uriel and Gaëtan Veste and Biel Martinez and Jing Li and Benoît Sklénard and Yann-Michel Niquet
Physical Review B, 108, 205416 (2023)
Abstract We investigate the existence of linear-in-momentum spin-orbit interactions in the valence band of Ge/GeSi heterostructures using an atomistic tight-binding method. We show that symmetry breaking at the Ge/GeSi interfaces gives rise to a linear Dresselhaus-type interaction for heavy-holes. This interaction results from the heavy-hole/light-hole mixings induced by the interfaces and can be captured by a suitable correction to the minimal Luttinger-Kohn, four bands kp Hamiltonian. It is dependent on the steepness of the Ge/GeSi interfaces, and is suppressed if interdiffusion is strong enough. Besides the Dresselhaus interaction, the Ge/GeSi interfaces also make a contribution to the in-plane gyromagnetic g-factors of the holes. The tight-binding calculations also highlight the existence of a small linear Rashba interaction resulting from the couplings between the heavy-hole/light-hole manifold and the conduction band enabled by the low structural symmetry of Ge/GeSi heterostructures. These interactions can be leveraged to drive the hole spin. The linear Dresselhaus interaction may, in particular, dominate the physics of the devices for out-of-plane magnetic fields. When the magnetic field lies in-plane, it is, however, usually far less efficient than the g-tensor modulation mechanisms arising from the motion of the dot in non-separable, inhomogeneous electric fields and strains.

Phys. Rev. B arXiv

Hole spin driving by strain-induced spin-orbit interactions
José Carlos Abadillo-Uriel, Esteban A. Rodríguez-Mena, Biel Martinez and Yann-Michel Niquet
Physical Review Letters, 131, 097002 (2023)
Abstract Hole spins in semiconductor quantum dots can be efficiently manipulated with radio-frequency electric fields owing to the strong spin-orbit interactions in the valence bands. Here we show that the motion of the dot in inhomogeneous strain fields gives rise to linear Rashba spin-orbit interactions (with spatially dependent spin-orbit lengths) and \(g\)-factor modulations that allow for fast Rabi oscillations. Such inhomogeneous strains build up spontaneously in the devices due to process and cool down stress. We discuss spin qubits in Ge/GeSi heterostructures as an illustration. We highlight that Rabi frequencies can be enhanced by one order of magnitude by shear strain gradients as small as \(3\times 10^{-6}\,\mathrm{nm}^{-1}\) within the dots. This underlines that spin in solids can be very sensitive to strains and opens the way for strain engineering in hole spin devices for quantum information and spintronics.

Phys. Rev. Lett. arXiv