447 research outputs found
Tunable Superconducting Properties of a-NbSi Thin Films and Application to Detection in Astrophysics
We report on the superconducting properties of amorphous NbxSi1-x thin films.
The normal-state resistance and critical temperatures can be separately
adjusted to suit the desired application. Notably, the relatively low
electron-phonon coupling of these films makes them good candidates for an "all
electron bolometer" for Cosmological Microwave Background radiation detection.
Moreover, this device can be made to suit both high and low impedance readouts
Thermally-Stimulated Current Investigation of Dopant-Related D- and A+ Trap Centers in Germanium for Cryogenic Detector Applications
International audienceThermally-stimulated current measurements provide a sensitive tool to char-acterize carrier traps in germanium detectors for dark matter search. Using this technique at cryogenic temperatures, very shallow traps have been detected with binding energies of a fraction of a meV, associated with the dopant species in the D-(A+) charge states. A positive identification of these traps is achieved through an analysis of the field dependence of the carrier emission rates, which demonstrates a potential well for the trapped carriers in the form of a polarization well in r-4, consistent with Lax's model for carrier trapping by a neutral center. The density of these traps is assessed, and implications for the space-charge cancellation procedure in cryogenic Ge detectors are discussed
Niobium Silicon alloys for Kinetic Inductance Detectors
We are studying the properties of Niobium Silicon amorphous alloys as a
candidate material for the fabrication of highly sensitive Kinetic Inductance
Detectors (KID), optimized for very low optical loads. As in the case of other
composite materials, the NbSi properties can be changed by varying the relative
amounts of its components. Using a NbSi film with T_c around 1 K we have been
able to obtain the first NbSi resonators, observe an optical response and
acquire a spectrum in the band 50 to 300 GHz. The data taken show that this
material has very high kinetic inductance and normal state surface resistivity.
These properties are ideal for the development of KID. More measurements are
planned to further characterize the NbSi alloy and fully investigate its
potential.Comment: Accepted for publication on Journal of Low Temperature Physics.
Proceedings of the LTD15 conference (Caltech 2013
Background suppression in massive TeO bolometers with Neganov-Luke amplified light detectors
Bolometric detectors are excellent devices for the investigation of
neutrinoless double-beta decay (0). The observation of such
decay would demonstrate the violation of lepton number, and at the same time it
would necessarily imply that neutrinos have a Majorana character. The
sensitivity of cryogenic detectors based on TeO is strongly limited by the
alpha background in the region of interest for the 0 of
Te. It has been demonstrated that particle discrimination in TeO
bolometers is possible measuring the Cherenkov light produced by particle
interactions. However an event-by-event discrimination with NTD-based light
detectors has to be demonstrated. We will discuss the performance of a
highly-sensitive light detector exploiting the Neganov-Luke effect for signal
amplification. The detector, being operated with NTD-thermistor and coupled to
a 750 g TeO crystal, shows the ability for an event-by-event identification
of electron/gamma and alpha particles. The extremely low detector baseline
noise, RMS 19 eV, demonstrates the possibility to enhance the sensitivity of
TeO-based 0 experiment to an unprecedented level
Rejection of randomly coinciding events in LiMoO scintillating bolometers using light detectors based on the Neganov-Luke effect
Random coincidences of nuclear events can be one of the main background
sources in low-temperature calorimetric experiments looking for neutrinoless
double-beta decay, especially in those searches based on scintillating
bolometers embedding the promising double-beta candidate Mo, because of
the relatively short half-life of the two-neutrino double-beta decay of this
nucleus. We show in this work that randomly coinciding events of the
two-neutrino double decay of Mo in enriched LiMoO
detectors can be effectively discriminated by pulse-shape analysis in the light
channel if the scintillating bolometer is provided with a Neganov-Luke light
detector, which can improve the signal-to-noise ratio by a large factor,
assumed here at the level of on the basis of preliminary
experimental results obtained with these devices. The achieved pile-up
rejection efficiency results in a very low contribution, of the order of counts/(keVkgy), to the background counting rate
in the region of interest for a large volume ( cm)
LiMoO detector. This background level is very encouraging in
view of a possible use of the LiMoO solution for a bolometric
tonne-scale next-generation experiment as that proposed in the CUPID project
Bi-layer Kinetic Inductance Detectors for space observations between 80-120 GHz
We have developed Lumped Element Kinetic Inductance Detectors (LEKID)
sensitive in the frequency band from 80 to 120~GHz. In this work, we take
advantage of the so-called proximity effect to reduce the superconducting gap
of Aluminium, otherwise strongly suppressing the LEKID response for frequencies
smaller than 100~GHz. We have designed, produced and optically tested various
fully multiplexed arrays based on multi-layers combinations of Aluminium (Al)
and Titanium (Ti). Their sensitivities have been measured using a dedicated
closed-circle 100 mK dilution cryostat and a sky simulator allowing to
reproduce realistic observation conditions. The spectral response has been
characterised with a Martin-Puplett interferometer up to THz frequencies, and
with a resolution of 3~GHz. We demonstrate that Ti-Al LEKID can reach an
optical sensitivity of about ~ (best pixel), or
~ when averaged over the whole array. The optical
background was set to roughly 0.4~pW per pixel, typical for future space
observatories in this particular band. The performance is close to a
sensitivity of twice the CMB photon noise limit at 100~GHz which drove the
design of the Planck HFI instrument. This figure remains the baseline for the
next generation of millimetre-wave space satellites.Comment: 7 pages, 9 figures, submitted to A&
First test of an enriched CdWO scintillating bolometer for neutrinoless double-beta-decay searches
For the first time, a cadmium tungstate crystal scintillator enriched in
Cd has been succesfully tested as a scintillating bolometer. The
measurement was performed above ground at a temperature of 18 mK. The crystal
mass was 34.5 g and the enrichment level ~82 %. Despite a substantial pile-up
effect due to above-ground operation, the detector demonstrated a high energy
resolution (2-7 keV FWHM in 0.2-2.6 MeV energy range), a powerful
particle identification capability and a high level of internal radiopurity.
These results prove that cadmium tungstate is an extremely promising detector
material for a next-generation neutrinoless double-beta decay bolometric
experiment, like that proposed in the CUPID project (CUORE Upgrade with
Particle IDentification)
Observation of the Nernst signal generated by fluctuating Cooper pairs
Long-range order is destroyed in a superconductor warmed above its critical
temperature (Tc). However, amplitude fluctuations of the superconducting order
parameter survive and lead to a number of well established phenomena such as
paraconductivity : an excess of charge conductivity due to the presence of
short-lived Cooper pairs in the normal state. According to an untested theory,
these pairs generate a transverse thermoelectric (Nernst) signal. In amorphous
superconducting films, the lifetime of Cooper pairs exceeds the elastic
lifetime of quasi-particles in a wide temperature range above Tc; consequently,
the Cooper pairs Nernst signal dominate the response of the normal electrons
well above Tc. In two dimensions, the magnitude of the expected signal depends
only on universal constants and the superconducting coherence length, so the
theory can be unambiguously tested. Here, we report on the observation of a
Nernst signal in such a superconductor traced deep into the normal state. Since
the amplitude of this signal is in excellent agreement with the theoretical
prediction, the result provides the first unambiguous case for a Nernst effect
produced by short-lived Cooper pairs
Measurements of the Complex Conductivity of NbxSi1-x Alloys on the Insulating Side of the Metal-Insulator Transition
We have conducted temperature and frequency dependent transport measurements
in amorphous Nb_x Si_{1-x} samples in the insulating regime. We find a
temperature dependent dc conductivity consistent with variable range hopping in
a Coulomb glass. The frequency dependent response in the millimeter-wave
frequency range can be described by the expression with the exponent somewhat smaller than one. Our ac
results are not consistent with extant theories for the hopping transport.Comment: 4 pages with 3 figures; published version has a different title from
original (was: "Electrodynamics in a Coulomb glass"
ZnO-based scintillating bolometers: New prospects to study double beta decay of Zn
The first detailed study on the performance of a ZnO-based cryogenic
scintillating bolometer as a detector to search for rare processes in zinc
isotopes was performed. A 7.2 g ZnO low-temperature detector, containing more
than 80\% of zinc in its mass, exhibits good energy resolution of baseline
noise 1.0--2.7 keV FWHM at various working temperatures resulting in a
low-energy threshold for the experiment, 2.0--6.0 keV. The light yield for
/ events was measured as 1.5(3) keV/MeV, while it varies for
particles in the range of 0.2--3.0 keV/MeV. The detector demonstrate
an effective identification of the / events from events
using time-properties of only heat signals. %(namely, Rise time parameter). The
radiopurity of the ZnO crystal was evaluated using the Inductively Coupled
Plasma Mass Spectrometry, an ultra-low-background High Purity Ge
-spectrometer, and bolometric measurements. Only limits were set at the
level of (1--100) mBq/kg on activities of \Nuc{K}{40},
\Nuc{Cs}{137} and daughter nuclides from the U/Th natural decay chains. The
total internal -activity was calculated to be 22(2) mBq/kg, with a
major contribution caused by 6(1) mBq/kg of \Nuc{Th}{232} and 12(2) mBq/kg of
\Nuc{U}{234}. Limits on double beta decay (DBD) processes in \Nuc{Zn}{64} and
\Nuc{Zn}{70} isotopes were set on the level of
-- yr for various decay modes profiting from 271
h of acquired background data in the above-ground lab. This study shows a good
potential for ZnO-based scintillating bolometers to search for DBD processes of
Zn isotopes, especially in \Nuc{Zn}{64}, with the most prominent spectral
features at 10--20 keV, like the two neutrino double electron capture. A
10 kg-scale experiment can reach the experimental sensitivity at the level of
yr.Comment: Prepared for submission to JINST; 27 pages, 9 figures, and 7 table
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