28 research outputs found
Phonon-mediated spin dynamics in a two-electron double quantum dot under a phonon temperature gradient
We have theoretically studied phonon-mediated spin-flip processes of
electrons in a GaAs double quantum dot (DQD) holding two spins, under a phonon
temperature gradient over the DQD. Transition rates of inter-dot
phonon-assisted tunnel processes and intra-dot spin-flip processes involving
spin triplet states are formalized by the electron-phonon interaction
accompanied with the spin-orbit interaction. The calculations of the spin-flip
rates and the occupation probabilities of the spin-states in the two-electron
DQD with respect to the phonon temperature difference between the dots are
quantitatively consistent with our previous experiment. This theoretical study
on the temperature gradient effect onto spins in coupled QDs would be essential
for understanding spin-related thermodynamic physics
Equal-Spin Andreev Reflection in Junctions of Spin-Resolved Quantum Hall Bulk State and Spin-Singlet Superconductor
The recent development of superconducting spintronics has revealed the
spin-triplet superconducting proximity effect from a spin-singlet
superconductor into a spin-polarized normal metal. In addition recently
superconducting junctions using semiconductors are in demand for highly
controlled experiments to engineer topological superconductivity. Here we
report experimental observation of Andreev reflection in junctions of
spin-resolved quantum Hall (QH) states in an InAs quantum well and the
spin-singlet superconductor NbTi. The measured conductance indicates a sub-gap
feature and two peaks on the outer side of the sub-gap feature in the QH
plateau-transition regime increases. The observed structures can be explained
by considering transport with Andreev reflection from two channels, one
originating from equal-spin Andreev reflection intermediated by spin-flip
processes and second arising from normal Andreev reflection. This result
indicates the possibility to induce the superconducting proximity gap in the
the QH bulk state, and the possibility for the development of superconducting
spintronics in semiconductor devices
Half-Integer Shapiro Steps in a Short Ballistic InAs Nanowire Josephson Junction
We report on half-integer Shapiro steps observed in an InAs nanowire
Josephson junction. We observed the Shapiro steps of the short ballistic InAs
nanowire Josephson junction and found anomalous half-integer steps in addition
to the conventional integer steps. The half-integer steps disappear as the
temperature increases or transmission of the junction decreases. These
experimental results agree closely with numerical calculation of the Shapiro
response for the skewed current phase relation in a short ballistic Josephson
junction
Observation of finite excess noise in the voltage-biased quantum Hall regime as a precursor for breakdown
We performed noise measurements in a two-dimensional electron gas to
investigate the nonequilibrium quantum Hall effect (QHE) state. While excess
noise is perfectly suppressed around the zero-biased QHE state reflecting the
dissipationless electron transport of the QHE state, considerable finite excess
noise is observed in the breakdown regime of the QHE. The noise temperature
deduced from the excess noise is found to be of the same order as the energy
gap between the highest occupied Landau level and the lowest empty one.
Moreover, unexpected finite excess noise is observed at a finite source-drain
bias voltagesmaller than the onset voltage of the QHE breakdown, which
indicates finite dissipation in the QHE state and may be related to the
prebreakdown of the QHE.Comment: 8 pages, 8 figure
Dominant non-local superconducting proximity effect due to electron-electron interaction in a ballistic double nanowire
Cooper pair splitting (CPS) can induce non-local correlation between two
normal conductors coupling to a superconductor. CPS into a double
one-dimensional electron gas is an appropriate platform for extracting large
amount of entangled electron pairs and one of the key ingredients for
engineering Majorana Fermions with no magnetic field. Here we study CPS using a
Josephson junction of a gate-tunable ballistic InAs double nanowire. The
measured switching current into the two nanowires significantly larger than sum
of that into the respective nanowires, indicating the inter-wire
superconductivity dominant compared to the intra-wire superconductivity. From
dependence on the number of propagating channels in the nanowires, the observed
CPS is assigned to one-dimensional electron-electron interaction. Our results
will pave the way for utilizing one-dimensional electron-electron interaction
to reveal physics of high-efficient CPS and engineer Majorana Fermions in
double nanowire systems via CPS