Jacques Chaussy

Measurement of the thermal conductance of silicon nanowires at low temperature

We have performed thermal conductance measurements on individual single-crystalline silicon suspended nanowires. The nanowires (130nm thick and 200nm wide) are fabricated by e-beam lithography and suspended between two separated pads on silicon on insulator substrate. We measure the thermal conductance of the phonon waveguide by the 3ω method. The cross section of the nanowire approaches the dominant phonon wavelength in silicon which is of the order of 100nm at 1K. Above 1.3K the conductance behaves as T3, but a deviation is measured at the lowest temperature which can be attributed to the reduced geometry.

A very sensitive microcalorimetry technique for measuring specific heat of μg single crystals

A microcalorimetry technique allowing one to measure the specific heat of bulk single crystals of a mass typically 10u2009μg, with a relative resolution Δc/c of 10−4 is presented. The well known ac steady state technique is employed. The sample holder is a polymer membrane with lithographically patterned thermometer and heaters made out of metallic thin films. The diameter of the useful area is 0.6 mm and the specific heat of the addendum is 1.5u2009μJ/K at 100 K. The sample is thermally coupled to the membrane through a gold thin film sputtered on its surface. The thermal coupling time constant of the sample is ∼5u2009ms, allowing to work at frequencies of 10 Hz. The method was applied to small single crystals of YBCO, providing the specific heat jump at the superconducting transition with a relative resolution of 10−2 and a precision of 10−1. The method is optimized at the temperature range 40–160 K, but can easily be modified for lower temperatures.

Liquid nitrogen to room-temperature thermometry using niobium nitride thin films

Niobium nitride thin-film thermometry has been developed for the temperature range of 70 to 300 K. The deposition parameters have been optimized in order to get the best performances, i.e., the highest temperature coefficient of resistance (TCR), up to 300 K. The TCR is found to be largely higher than 1% as the temperature is lowered from 300 K, up to 6% at 77 K. These significant performances are compared to the one of regular platinum thermometer as well as to other resistive thermometer: semiconductor type or amorphous metal to insulator transition materials. It is discussed how the properties of the NbN thin films could be due to a high-temperature Mott transition.

High rayleigh number convection with gaseous helium at low temperature

This article presents an experimental set-up to study the turbulent regime of free thermal convection in a Rayleigh-Bénard cell. Helium gas around 4 K is confined in a cell of aspect ratio 0.5. With a thermocouple technique we can measure temperature differences across the cell as low as 0.2 mK, which allows to test the adiabatic gradient effect. Covering a large range of Rayleigh numbers (103 to 5 × 1012), Nusselt numbers from 1 to 103 are obtained. The results are compared with previous works. They show a departure from the 2/7 power law above Ra = 3 × 1010.

Noise measurements on silicon J‐FETs at low temperature using a very high Q superconducting resonator

Noise voltage and noise current measurements have been carried out at different temperatures on two kinds of low‐noise silicon J‐FET at moderately high frequencies up to 100 kHz. We have made careful noise current measurements by constructing a very low‐loss superconducting resonator working in the kHz frequency range, whose quality factor reaches 3×105. At 10 kHz, the measured noise energy lies between 1.1 and 1.8×10−24 W/Hz for both types of transistors, but the ratio between the noise voltage and the noise current exhibits pronounced differences depending on the device under test.

Thermal signatures of the Little-Parks effect in the heat capacity of mesoscopic superconducting rings

We present measurements of thermal signatures of the Little-Parks effect using a highly sensitive nanocalorimeter. Small variations of the heat capacity

Miniature low‐temperature high‐frequency filters for single electronics

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A very sensitive technique for measuring the temperature derivative of electrical resistance between 4 and 300 K

of 2.5 millions of noninteracting micrometer-sized superconducting rings threaded by a magnetic flux

Electrical and thermal conductivities of magnetically melt textured YBa2Cu3O7−δ

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Thin gold wires as reference for thermoelectric power measurements of small samples from 1.3 K to 350 K

have been measured by attojoule calorimetry. This noninvasive method allows the measurement of thermodynamic propertieschar22{}and hence the probing of the energy levelschar22{}of nanosystems without perturbing them electrically. It is observed that