Cryogenic Differential Amplifier for NMR Applications

We have designed and characterized a cryogenic amplifier for use in 3 He NMR spectrometry. The amplifier, with a power consumption of ∼ 2.5  mW, works at temperatures down to 4 K. It has a high-impedance input for measuring a signal from NMR resonant circuit, and a 50  Ω differential input which can be used for pick-up compensation and gain calibration. At 4.2 K, the amplifier has a voltage gain of 45, output resistance 146  Ω and a 4.4 MHz bandwidth starting from DC. At 1 MHz, the voltage and current noise amount to 1.3  nV / Hz and 12  fA / Hz , respectively, which yields an optimal source impedance of ∼ 100  k Ω .

Recombination-limited energy relaxation in a Bardeen-Cooper-Schrieffer superconductor

We study quasiparticle energy relaxation at subkelvin temperatures by injecting hot electrons into an Al island and measuring the energy flux from quasiparticles into phonons both in the superconducting and in the normal state. The data show strong reduction of the flux at low temperatures in the superconducting state, in qualitative agreement with the theory for clean superconductors. However, quantitatively the energy flux exceeds the theoretical predictions both in the superconducting and in the normal state, suggesting an enhanced or additional relaxation process.

Manipulation and generation of supercurrent in out-of-equilibrium Josephson tunnel nanojunctions

We demonstrate experimentally the manipulation of supercurrent in Al-AlOx-Ti Josephson tunnel junctions by injecting quasiparticles in a Ti island from two additional tunnel-coupled Al superconducting reservoirs. Both supercurrent enhancement and quenching with respect to equilibrium are achieved. We demonstrate cooling of the Ti line by quasiparticle injection from the normal state deep into the superconducting phase. A model based on heat transport and the nonmonotonic current-voltage characteristic of a Josephson junction satisfactorily accounts for our findings.

Limitations in cooling electrons using normal-metal-superconductor tunnel junctions

We demonstrate both theoretically and experimentally two limiting factors in cooling electrons using biased tunnel junctions to extract heat from a normal metal into a superconductor. First, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do not obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Second, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.

[Apparatus correction of contractures of the joints of the lower limbs in patients with infantile cerebral palsy]

The method of treatment with the application of compression-distraction apparatus is described. An analysis of remote results of the treatment of 57 patients is given.