2 research outputs found
Hyperfine-phonon spin relaxation in a single-electron GaAs quantum dot
Understanding and control of the spin relaxation time T-1 is among the key challenges for spinbased qubits. A larger T-1 is generally favored, setting the fundamental upper limit to the qubit coherence and spin readout fidelity. In GaAs quantum dots at low temperatures and high inplane magnetic fields B, the spin relaxation relies on phonon emission and spin-orbit coupling. The characteristic dependence T-1 alpha B-5 and pronounced B-field anisotropy were already confirmed experimentally. However, it has also been predicted 15 years ago that at low enough fields, the spin-orbit interaction is replaced by the coupling to the nuclear spins, where the relaxation becomes isotropic, and the scaling changes to T-1 alpha B-3. Here, we establish these predictions experimentally, by measuring T-1 over an unprecedented range of magnetic fields-made possible by lower temperature-and report a maximum T-1 = 57 +/- 15 s at the lowest fields, setting a record electron spin lifetime in a nanostructure
Characterization of Hydrogen Plasma Defined Graphene Edges
We investigate the quality of hydrogen plasma defined graphene edges by Raman
spectroscopy, atomic resolution AFM and low temperature electronic transport
measurements. The exposure of graphite samples to a remote hydrogen plasma
leads to the formation of hexagonal shaped etch pits, reflecting the anisotropy
of the etch. Atomic resolution AFM reveals that the sides of these hexagons are
oriented along the zigzag direction of the graphite crystal lattice and the
absence of the D-peak in the Raman spectrum indicates that the edges are high
quality zigzag edges. In a second step of the experiment, we investigate
hexagon edges created in single layer graphene on hexagonal boron nitride and
find a substantial D-peak intensity. Polarization dependent Raman measurements
reveal that hydrogen plasma defined edges consist of a mixture of zigzag and
armchair segments. Furthermore, electronic transport measurements were
performed on hydrogen plasma defined graphene nanoribbons which indicate a high
quality of the bulk but a relatively low edge quality, in agreement with the
Raman data. These findings are supported by tight-binding transport
simulations. Hence, further optimization of the hydrogen plasma etching
technique is required to obtain pure crystalline graphene edges.Comment: 10 pages, 7 figure