501 research outputs found
Spin Hall effect at interfaces between HgTe/CdTe quantum wells and metals
We study the spin-dependent transmission through interfaces between a
HgTe/CdTe quantum well (QW) and a metal - both for the normal metal and the
superconducting case. Interestingly, we discover a new type of spin Hall effect
at these interfaces that happens to exist even in the absence of structure and
bulk inversion asymmetry within each subsystem (i.e. the QW and the metal).
Thus, this is a pure boundary spin Hall effect which can be directly related to
the existence of exponentially localized edge states at the interface. We
demonstrate how this effect can be measured and functionalized for an
all-electric spin injection into normal metal leads.Comment: 7 pages, 6 figure
Interplay of bulk and edge states in transport of two-dimensional topological insulators
We study transport in two-terminal metal/quantum spin-Hall insulator
(QSHI)/metal junctions. We show that the conductance signals originating from
the bulk and the edge contributions are not additive. While for a long junction
the transport is determined by the edge states contribution, for a short
junction, the conductance signal is built from both bulk and edge states in the
ratio which depends on the width of the sample. Further, in the topological
insulator regime the conductance for short junctions shows a non-monotonic
behavior as a function of the sample length. Surprisingly this non-monotonic
behavior of conductance can be traced to the formation of an effectively
propagating solution which is robust against scalar disorder. Our predictions
should be experimentally verifiable in HgTe QWs and BiSe thin films.Comment: 9 pages, 8 figure
How to Distinguish between Specular and Retroconfigurations for Andreev Reflection in Graphene Rings
We numerically investigate Andreev reflection in a graphene ring with one
normal conducting and one superconducting lead by solving the Bogoliubov--de
Gennes equation within the Landauer-B\"uttiker formalism. By tuning chemical
potential and bias voltage, it is possible to switch between regimes where
electron and hole originate from the same band (retroconfiguration) or from
different bands (specular configuration) of the graphene dispersion,
respectively. We find that the dominant contributions to the Aharonov-Bohm
conductance oscillations in the subgap transport are of period in
retroconfiguration and of period in specular configuration, confirming
the predictions obtained from a qualitative analysis of interfering scattering
paths. Because of the robustness against disorder and moderate changes to the
system, this provides a clear signature to distinguish both types of Andreev
reflection processes in graphene.Comment: 5 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1201.620
Signatures of topology in ballistic bulk transport of HgTe quantum wells
We calculate bulk transport properties of two-dimensional topological
insulators based on HgTe quantum wells in the ballistic regime. Interestingly,
we find that the conductance and the shot noise are distinctively different for
the so-called normal regime (the topologically trivial case) and the so-called
inverted regime (the topologically non-trivial case). Thus, it is possible to
verify the topological order of a two-dimensional topological insulator not
only via observable edge properties but also via observable bulk properties.
This is important because we show that under certain conditions the bulk
contribution can dominate the edge contribution which makes it essential to
fully understand the former for the interpretation of future experiments in
clean samples.Comment: 5 pages, 4 figure
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