85 research outputs found
Andreev reflection of quantum Hall states through a quantum point contact
We investigate the interplay between the quantum Hall (QH) effect and
superconductivity in InAs surface quantum well (SQW)/NbTiN heterostructures
using a quantum point contact (QPC). We use QPC to control the proximity of the
edge states to the superconductor. By measuring the upstream and downstream
resistances of the device, we investigate the efficiency of Andreev conversion
at the InAs/NbTiN interface. Our experimental data is analyzed using the
Landauer-Buttiker formalism, generalized to allow for Andreev reflection
processes. We show that by varying the voltage of the QPC, , the
average Andreev reflection, , at the QH-SC interface can be tuned from 50%
to 10%. The evolution of with extracted from the measurements
exhibits plateaus separated by regions for which varies continuously with
. The presence of plateaus suggests that for some ranges of
the QPC might be pinching off almost completely from the QH-SC interface some
of the edge modes. Our work shows a new experimental setup to control and
advance the understanding of the complex interplay between superconductivity
and QH effect in two-dimensional gas systems
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