109 research outputs found
Thermoelectrics with Coulomb coupled quantum dots
In this article we review the thermoelectric properties of three terminal
devices with Coulomb coupled quantum dots (QDs) as observed in recent
experiments [1,2]. The system we consider consists of two Coulomb-blockade QDs
one of which can exchange electrons with only a single reservoir (heat
reservoir) while the other dot is tunnel coupled to two reservoirs at a lower
temperature (conductor). The heat reservoir and the conductor interact only via
the Coulomb-coupling of the quantum dots. It has been found that two regimes
have to be considered. In the first one heat flow between the two systems is
small. In this regime thermally driven occupation fluctuations of the hot QD
modify the transport properties of the conductor system. This leads to an
effect called thermal gating. Experiment have shown how this can be used to
control charge flow in the conductor by means of temperature in a remote
reservoir. We further substantiate the observations with model calculations and
implications for the realization of an all-thermal transistor are discussed. In
the second regime, heat flow between the two systems is relevant. Here the
system works as a nano scale heat engine, as proposed recently [3]. We review
the conceptual idea, its experimental realization and the novel features
arising in this new kind of thermoelectric device such as decoupling of heat
and charge flow.Comment: 18 pages, 10 figures, submitted to Comptes Rendue Physiqu
The topological Faraday effect cannot be observed in a realistic sample
A striking feature of 3 dimensional (3D) topological insulators (TIs) is the
theoretically expected topological magneto-electric (TME) effect, which gives
rise to additional terms in Maxwell's laws of electromagnetism with an
universal quantized coefficient proportional to half-integer multiples of the
fine structure constant . In an ideal scenario one therefore expects
also quantized contributions in the magneto-optical response of TIs. We review
this premise by taking into account the trivial dielectric background of the TI
bulk and potential host substrates, and the often present contribution of
itinerant bulk carriers. We show that (i) one obtains a non-universal
magneto-optical response whenever there is impedance mismatch between different
layers and (ii) that the detectable signals due to the TME rapidly approach
vanishingly small values as the impedance mismatch is detuned from zero. We
demonstrate that it is methodologically impossible to deduce the existence of a
TME exclusively from an optical experiment in the thin film limit of 3D TIs at
high magnetic fields
Proximity Induced Superconductivity in CdTe-HgTe Core-Shell Nanowires
In this letter we report on proximity superconductivity induced in CdTe-HgTe
core-shell nanowires, a quasi-one-dimensional heterostructure of the
topological insulator HgTe. We demonstrate a Josephson supercurrent in our
nanowires contacted with superconducting Al leads. The observation of a sizable
product, a positive excess current and multiple Andreev reflections
up to fourth order further indicate a high interface quality of the junctions.Comment: Accepted for publication in Nano Letter
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