Response time of a thermometer based on normal metal-insulator-superconductor (NIS) tunnel junctions (original) (raw)
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Mesoscopic superconducting tunnel junction devices : experimental studies of performance limitations
2005
In this work four different mesoscopic superconducting devices have been experimentally studied: an ammeter based on a hysteretic Josephson junction switching from the superconducting state to the normal state, a conventional Cooper pair pump (CPP) based on two superconducting islands separated by tunnel junctions, a novel flux assisted Cooper pair pump and a thermometer based on a tunnel junction between a superconductor and a normal metal. These devices make use of phenomena related to superconductivity and are also benefiting from some properties of small structures, e.g., of quantum mechanical tunneling and of transport of single electrons. The present research focused on investigating performance limitations of these devices and the aim was to improve their performance. A hysteretic Josephson junction switching can be used as a sensitive current threshold detector. For many purposes, a smaller critical current I_c of the detecting junction would yield a higher current sensitivity. It was found in this Thesis that the main limitation of the ammeter is that with increasing sensitivity the negative effects due to dissipation start to dominate. In this Thesis the Josephson junction was also demonstrated as a shot-noise detector, and it was concluded that this kind of a device could probably be made into an absolute on-chip detector of Fano-factors and noise in general. A charge pump is a device which can periodically transfer a discrete amount of charge Q through an electrical circuit. The measured double island CPP introduced a frequency dependent current with a value close to the expected one at low pumping frequencies. The drawback in the measurements was that the direction of the pumped current was set by the bias voltage. The results of the measurement on flux assisted pumping were indeed very promising and the studied device was able to produce sufficiently high pumped currents of around 0.1 nA with reasonable accuracy. Thermometer based on NIS (Normal metal-Insulator-Superconductor) tunnel junctions is a very promising temperature sensor for bolometric radiation sensor applications. This work showed that it can be used as a sensitive thermometer up to MHz frequencies range and that its response time is limited by the electron-phonon scattering rate. Josephson junction, phase diffusion, Cooper pair pump, NIS tunnel junction 165 951-22-7709-3
Theory of temperature fluctuation statistics in superconductor-normal metal tunnel structures
Physical Review B, 2012
We present the theory of temperature fluctuation statistics for a SINIS structure, where a normal metal island (N) is coupled by tunnel junctions (I) to two superconducting leads (S). Under certain conditions, this structure exhibits manifestly non-Gaussian fluctuations of temperature. Here we detail the necessary requirements for their observation.
On a Possibility to Measure Thermo-Electric Power in SNS Structures
Modern Physics Letters B, 1998
Two dissimilar Josephson junctions, which are connected to a heater can act as precise batteries. Because of the difference in thermoelectric power of these batteries, circuit with two dissimilar batteries, under heat flow ∆T ∼ 10 −5 K would have a net EMF 10 −11 V around the zero-resistance loop leading to a loop's magnetic flux oscillating in time. It is shown its theoretical value is proportional to both the temperature difference as well as the disparity in the thermoelectric powers of the two junctions.
Limitations in Cooling Electrons using Normal-Metal-Superconductor Tunnel Junctions
Physical Review Letters, 2004
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. Firstly, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do no more obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Secondly, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.
Optimization of electron cooling by SIN tunnel junctions
Superconductor Science and Technology, 2004
We report on the optimization of electron cooling by SIN tunnel junctions due to the advanced geometry of superconducting electrodes and very effective normal metal traps for more efficient removal of quasiparticles at temperatures from 25 to 500 mK. The maximum decrease in electron temperature of about 200 mK has been observed at bath temperatures 300-350 mK. We used four-junction geometry with Al-AlO x -Cr/Cu tunnel junctions and Au traps. Efficient electron cooling was realized due to the improved geometry of the cooling tunnel junctions (quadrant shape of the superconducting electrode) and optimized Au traps just near the junctions (≈0.5 µm) to reduce reabsorption of quasiparticles after removing them from normal metal. The maximum cooling effect was increased from a temperature drop of dT = −56 mK (ordinary cross geometry) to −130 mK (improved geometry of superconducting electrodes) and to dT = −200 mK (improved geometry of superconducting electrodes and effective Au traps).
Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions
Beilstein Journal of Nanotechnology, 2016
Background: Thermoelectric effects result from the coupling of charge and heat transport and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron–hole symmetry, which is usually quite small in metal structures. In addition, thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime. Results: We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction. Conclusion: Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to t...
We propose and analyze a temperature-to-frequency converter based on a normal metal-ferromagnetic insulator-superconductor (NFIS) junction embedded in a superconducting loop which contains a superconducting quantum interference device (SQUID). By setting a temperature difference across the NFIS junction a thermovoltage will be generated across the circuit if the SQUID is in the resistive regime. This thermovoltage depends on both the magnitude and sign of the temperature difference, and will generate radiation at the Josephson frequency. In Eu-based FIs joined with superconducting Al the structure is in principle capable to generate frequencies up to sim120\sim 120sim120GHz, and transfer functions up to 200200200GHz/K at around sim1\sim 1sim1K. Yet, if operated as electron thermometer, the device may provide temperature noise better than 353535nK Hz$^{-1/2}$ thereby being potentially attractive for radiation sensing applications.
Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors
Physical Review Letters, 2010
We have found experimentally that the critical current of a square superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T . As a consequence, the effective transition temperature Tc of the TES is current-dependent and at fixed current scales as 1/L 2 . We also have found that the critical current can show clear Fraunhoferlike oscillations in an applied magnetic field, similar to those found in Josephson junctions. The observed behavior has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. We have observed the proximity effect in these devices over extraordinarily long lengths exceeding 100 µm. 74.78.Bz,74.25.Op A superconductor cooled through its transition temperature T c while carrying a finite dc bias current undergoes an abrupt decrease in electrical resistance from its normal-state value R N to zero.
Electronic cooling in superconducting tunnel junctions
Physics Letters a, 1997
The cooling power provided by the current through a superconductor/insulator/superconductor tunnel junction is studied theoretically. The influence of non-equilibrium distributions of the quasi-particles on the heat flow is analysed within a simple relaxation model. A superconducting gap enhancement can be explained within the equilibrium as well as the non-equilibrium model.