Shahal Ilani
addresses a highly fundamental question in a very novel and elegant approach.
The question is : « Can we make 2 electrons attract only via
repulsive interaction ? ».
Of course this
problem is particularly relevant in the framework of superconductors and in the
search for room-temperature superconductivity, since the lighter is glue, the
stronger is the coupling to be expected. The approach is here to specifically
design a minimal building block to obtain attraction between 2 electrons.
Starting from
ideas proposed by Little where a 1D conducting molecule is coupled to a
specific medium acting as an electronic polarizer and having negative
dielectric constant, Ilana and his group have designed a specific system made
of a very clean carbon nanotube
(CNT) containing two quantum wells and electrically connected to a measurement
setup. The electronic polarizer is
also a carbon nanotube with two quantum wells. When the electronic polarizer
(EP) is sufficiently far away, measurement of the voltages in the CNT shows
that the electrons in the two quantum wells repulse each other, as expected,
whereas when the EP is close to the CNT, the electrons are shown to attract
each other i.e. there is an observable quantum state resulting of superposition
of two simultaneously occupied and vacant quantum wells. The mechanism is that when the
electronic polarizer is approached to the CNT, the presence of an electron in
one of the quantum wells of the CNT will provoke the hopping of the electron
that is in the closest quantum well of the EP to the other (further) quantum
well, therefore creating an electric field of opposite sign. In order to share
the cost for the electrical field that is created, two electrons will have a
tendency to occupy/disoccupy simultaneously the nearest quantum wells on the
CNT.
The authors have
inspected the detuning dependence of the phenomenon and are currently exploring
transport in these devices.
Blogged by
Brigitte Leridon
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