Quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors

Nowadays superconductors serve in numerous applications, from high-field magnets to ultra-sensitive detectors of radiation. Mesoscopic superconducting devices, i.e. those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, e.g., leakage currents or decreased coherence times in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics which is in quantitative agreement with the experimental data

Ex-situ Tunnel Junction Process Technique Characterized by Coulomb Blockade Thermometry

We investigate a wafer scale tunnel junction fabrication method, where a plasma etched via through a dielectric layer covering bottom Al electrode defines the tunnel junction area. The ex-situ tunnel barrier is formed by oxidation of the bottom electrode in the junction area. Room temperature resistance mapping over a 150 mm wafer give local deviation values of the tunnel junction resistance that fall below 7.5 % with an average of 1.3 %. The deviation is further investigated by sub-1 K measurements of a device, which has one tunnel junction connected to four arrays consisting of N junctions (N = 41, junction diameter 700 nm). The differential conductance is measured in single-junction and array Coulomb blockade thermometer operation modes. By fitting the experimental data to the theoretical models we found an upper limit for the local tunnel junction resistance deviation of ~5 % for the array of 2N+1 junctions. This value is of the same order as the minimum detectable deviation defined by the accuracy of our experimental setup

Primary thermometry in the intermediate Coulomb blockade regime

We investigate Coulomb blockade thermometers (CBT) in an intermediate temperature regime, where measurements with enhanced accuracy are possible due to the increased magnitude of the differential conductance dip. Previous theoretical results show that corrections to the half width and to the depth of the measured conductance dip of a sensor are needed, when leaving the regime of weak Coulomb blockade towards lower temperatures. In the present work, we demonstrate experimentally that the temperature range of a CBT sensor can be extended by employing these corrections without compromising the primary nature or the accuracy of the thermometer.Comment: 8 pages, 4 figure

Double oxidation scheme for tunnel junction fabrication

The authors report a method to achieve Al–AlOx–Al tunnel junctions with high specific resistance in a controlled manner using a double oxidation technique. The technique is based on the standard method for oxidation repeated on an additional Al layer. The tunnel junctions were characterized with standard methods, such as comparison of room temperature resistance with liquid helium resistance and the authors found them to be of comparable quality to junctions fabricated with standard single oxidation. Fitting with the Simmons model suggests that both the barrier width and barrier height are consistent with those obtained in a single oxidation step. The junction specific capacitance was determined at low temperature to be 68fF/μm2. These junctions, employed in low temperature measurements and applications, demonstrate expected and stable conductance characteristics. The double oxidation method is straightforward to implement in a basic setup for tunnel junction fabrication.Peer reviewe

Director networks and informed traders

We provide evidence that sophisticated investors like short sellers, option traders, and financial institutions are more informed when trading stocks of companies with more connected board members. For firms with large director networks, the annualized return difference between the highest and lowest quintile of informed trading ranges from 4% to 7.2% compared to the same return difference in firms with less connected directors. Sophisticated investors better predict outcomes of upcoming earnings surprises and firm-specific news sentiment for companies with more connected directors. Changes in board connectedness are positively associated with changes in measures of adverse selection

Non-hysteretic superconducting quantum interference proximity transistor with enhanced responsivity

This Letter presents fabrication and characterization of an optimized superconducting quantum interference proximity transistor. The present device, characterized by reduced tunnel junction area and shortened normal-metal section, demonstrates no hysteresis at low temperatures as we increased the Josephson inductance of the weak link by decreasing its cross section. It has consequently almost an order of magnitude improved magnetic field responsivity as compared to the earlier design. The modulation of both the current and the voltage across the junction have been measured as a function of magnetic flux piercing the superconducting loop.Peer reviewe