Search results for "Tunnelling"
showing 10 items of 218 documents
Microrefrigeration by quasiparticle tunnelling in NIS and SIS junctions
2000
Abstract A solid-state refrigeration method at sub-kelvin temperatures has been developed. It is based on quasiparticle tunnelling between a superconductor and a normal metal, or, between two dissimilar superconducting metals. The refrigerator is fabricated by combining nanolithography and micromachining methods. This technique has been demonstrated in both electron cooling from 0.3 to 0.1 K and in refrigeration of a dielectric platform. We describe a new fabrication method of tunnel junctions in a shadow evaporation configuration using a mechanical mask of silicon nitride.
Cooling of a superconductor by quasiparticle tunneling
1999
We have extended the cryogenic cooling method based on tunneling between a superconductor and another metal to the case when both metals are superconducting but when their energy gaps are different; earlier, this method was applied between a superconductor and a normal metal. The electron system of a titanium strip with the superconducting transition temperature Tc2=0.51 K has been cooled from 1.02Tc2 to below 0.7Tc2 by this method, using aluminum as the other superconductor.
Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks
2013
We report on the transport properties of an array of N about 30 interconnected Nb nanowires, grown by sputtering on robust porous Si substrates. The analyzed system exhibits a broad resistive transition in zero magnetic field, H, and highly nonlinear V(I) characteristics as a function of H which can be both consistently described by quantum tunneling of phase slips.
Refrigeration of a dielectric membrane by superconductor/insulator/normalmetal/insulator/superconductor tunneling
1997
We have applied tunneling of electrons between a normal metal and a superconductor to refrigerate a thin dielectric membrane attached to the normal electrode of a superconductor/ insulator/normal-metal/insulator/superconductor (SINIS) structure. Starting from T≈200 mK, a decrease in temperature of several mK was observed, measured by a separate thermometer on the membrane. It should be straightforward to improve the refrigerator performance to the level of the recently demonstrated SINIS electron cooling method, such that the drop in the lattice temperature would be more than an order of magnitude larger.
Efficient electronic cooling in heavily doped silicon by quasiparticle tunneling
2001
Cooling of electrons in a heavily doped silicon by quasiparticle tunneling using a superconductor–semiconductor–superconductor double-Schottky-junction structure is demonstrated at low temperatures. In this work, we use Al as the superconductor and thin silicon-on-insulator (SOI) film as the semiconductor. The electron–phonon coupling is measured for the SOI film and the low value of the coupling is shown to be the origin of the observed significant cooling effect.
Comparison among superconducting models for β″-ET4[(H3O)Fe(C2O4)3]·C6H5Br single crystals by scanning tunnelling spectroscopy
2008
Single crystals of the novel superconductor beta ''-(BEDT-TTF)(4)[(H3O)Fe(C2O4)(3)]center dot C6H5Br charge-transfer salt were studied using a scanning tunnelling microscope. The measured samples have an onset critical temperature of about 4.0 K. Features often reported on similar compounds were observed in the tunnelling spectra at 1.4 K. STS spectra are compared with several models for the superconducting density of states. Our analysis evidences inhomogeneous superconductivity and indicates that the presence of a magnetic layer into the sample plays a role in determining the superconducting spectroscopic features. (C) 2008 Elsevier Masson SAS. All rights reserved.
Superconductivity mediated by spin fluctuations in the heavy-fermion compound UPd2 Al3
1999
It is well known that any weak attractive electron–electron interaction in metals can in principle cause the formation of Cooper pairs, which then condense into a superconducting ground state1. In conventional superconductors, this attractive interaction is mediated by lattice vibrations (phonons). But for the heavy-fermion and high-temperature superconductors, alternative pairing interactions are considered to be possible2. For example, the low-temperature properties of heavy-fermion systems are dominated by antiferromagnetic spin fluctuations, which have been considered theoretically3 as a possible cause for Cooper-pair formation. This picture recently received some experimental support: …
Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing
2006
We have observed that submicron sized Al--AlO{$_x$}--Al tunnel junctions can be stabilized completely by annealing them in vacuum at temperatures between $350^{\circ}$C and $450^{\circ}$C. In addition, low temperature characterization of the samples after the annealing treatment showed a marked improvement of the tunneling characteristics due to disappearance of unwanted resonances in the current. Charging energy, tunneling resistance, barrier thickness and height all increase after the treatment. The superconducting gap is not affected, but supercurrent is reduced in accordance with the increase of tunneling resistance.
Proximity-induced Josephson-quasiparticle process in a single-electron transistor
1998
We have performed the first experiments in a superconductor - normal metal - superconductor single electron transistor in which there is an extra superconducting strip partially overlapping the normal metal island in good metal-to-metal contact. Superconducting proximity effect gives rise to current peaks at voltages below the quasiparticle threshold. We interpret these peaks in terms of the Josephson-quasiparticle process and discuss their connection with the proximity induced energy gap in the normal metal island.
Scanning tunneling measurements of layers of superconducting 2H-TaSe2: Evidence for a zero-bias anomaly in single layers
2013
This work was supported by the EU (ERC Advanced Grant SPINMOL and COST MP-1201), the Spanish MINECO (Consolider-Ingenio in Molecular Nanoscience, CSD2007-00010 and projects FIS2011-23488, MAT2011-25046, MAT2011-22785 and ACI-2009-0905, co-financed by FEDER), by the Comunidad de Madrid (program Nanobiomagnet) and the Generalitat Valenciana (Programs Prometeo and ISIC-NANO)