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Jeudi 5 Decembre 2013, 14h
Amphi Holweck, Esc C, 1ème etage
Détection de photons et d’électrons uniques par des nanostructures supraconductrices
Michael Rostiche
LPA,ENS
In a superconducting nanowire (typically 100 nm wide, 10 nm deep), biased at a slightly subcritical current, an energy input in the electron-volt range is sufficient to initiate a detectable resistive transition. Single photon detection started a decade ago upon that principle by using NbN and NbTiN filaments whose capabilities, in terms of sensitivity, speed and dark count rate, compete favorably with other detection devices, particularly in the telecommunication range (1.3 µm – 1.55 µm). Here westudy the response of such nanostrips exposed successively to incident photonic and electronic irradiations. The electrons (10 keV to 20 keV) provided by the column of a scanning electron microscope allow us to demonstrate the single electron operation, with an intrinsic efficiency
close to unity. With this experimental setup, we could map the detection efficiency of a NbTiN nanowire meander with a spatial resolution better
than 100 nm. We have also investigated the influence of a magnetic field in photon counting experiments. On account of the magnetic sensitivity of these structures, it has been suggested to relate the dark counts, and the mechanism of detection itself, to vortex motion. Here we report the
influence of a perpendicular magnetic field, varying between 0 and 1
tesla, on the detection efficiency (DE) of single photons at 665 nm and
1500 nm, and on the dark count rate (DCR), by a NbTiN nanowire. With this experimental set-up we observe a clear increase of the DE and DCR at the magnetic field that allows the entrance and the motion of vortex in the width of the wire.