0000000000919374
AUTHOR
J. P. Pekola
Discrete saturation thickness and anomalous potential height of native ultrathin aluminum oxide tunnel barriers
We have investigated planar metal - insulator - metal tunnel junctions with aluminum oxide as dielectricum. These oxide barriers were grown on an aluminum electrode in pure oxygen at room temperature till saturation. We observed discrete barrier widths separated by \Delta s \approx 0.38 nm, corresponding to the addition of one layer of oxygen atoms. The minimum thickness of s_0 \approx 0.54 nm is due to a double layer of oxygen. We found a strong and systematic dependence of the barrier height \Phi_0 on the thickness s like \Phi_0 \approx 2.5 eV / s^2(nm), which nearly coincides with the kinetic electron energy E = h^2/2ms^2 for which the deBroglie wavelength matches the width of the barrie…
Noise in refrigerating tunnel junctions and in microbolometers
Microrefrigerators based on normal metal-insulator-superconductor (NIS) junctions represent a very attractive alternative to cool the microbolometers and calorimeters for astrophysical observations in space-borne experiments. The performance in such measurements requires a good knowledge of the noise sources in the detectors. In this paper we present detailed calculations of the thermal fluctuations and of the noise equivalent power due to the heat transfer through the NIS junctions or due to the thermal contact between different subsystems of the detector. The influence of the background radiation will also be evaluated. Analytical approximations, valid at low temperatures, are given.
Fluctuation superconductivity limited noise in a transition-edge sensor
In order to investigate the origin of the until now unaccounted excess noise and to minimize the uncontrollable phenomena at the transition in X-ray microcalorimeters we have developed superconducting transition-edge sensors into an edgeless geometry, the so-called Corbino disk (CorTES), with superconducting contacts in the centre and at the outer perimeter. The measured rms current noise and its spectral density can be modeled as resistance noise resulting from fluctuations near the equilibrium superconductor-normal metal boundary
Coulomb blockade nanothermometer
Reliable thermometry is normally based on commercial secondary sensors which are factory calibrated. Primary thermometers exist, too, but their use is limited because of intrinsic slowness, complex instrumentation, or inconvenient installation at the desired location. We have found that arrays of nanoscale tunnel junctions exhibit properties which are very suitable for primary and secondary cryogenic thermometry. Temperature range of this Coulomb blockade thermometer (CBT) extends over about two decades for one sensor and the mean temperature is lithographically adjustable. We have studied the performance of the CBT sensors at very low temperatures where the minimum temperature is limited b…
One and two dimensional tunnel junction arrays in weak Coulomb blockade regime-absolute accuracy in thermometry
We have investigated one and two dimensional (1D and 2D) arrays of tunnel junctions in partial Coulomb blockade regime. The absolute accuracy of the Coulomb blockade thermometer is influenced by the external impedance of the array, which is not the same in the different topologies of 1D and 2D arrays. We demonstrate, both by experiment and by theoretical calculations in simple geometries, that the 1D structures are better in this respect. Yet in both 1D and 2D, the influence of the environment can be made arbitrarily small by making the array sufficiently large.
Resonant tunneling through a macroscopic charge state in a superconducting SET transistor
We predict theoretically and observe in experiment that the differential conductance of a superconducting SET transistor exhibits a peak which is a complete analogue in a macroscopic system of a standard resonant tunneling peak associated with tunneling through a single quantum state. In particular, in a symmetric transistor, the peak height is universal and equal to $e^2/2\pi \hbar$. Away from the resonance we clearly observe the co-tunneling current which in contrast to the normal-metal transistor varies linearly with the bias voltage.