Cooper pair splitting in diffusive magnetic SQUIDs
We have employed noise thermometry for investigations of thermal relaxation between the electrons and the substrate in nanowires patterned from 40-nm-thick titanium film on top of silicon wafers covered by a native oxide. By controlling the electronic temperature Te by Joule heating at the base temperature of a dilution refrigerator, we probe the electron–phonon coupling and the thermal boundary resistance at temperatures Te = 0.5–3 K. Using a regular T 5-dependent electron–phonon coupling of clean metals and a T 4-dependent interfacial heat flow, we deduce a small contribution for the direct energy transfer from the titanium electrons to the substrate phonons due to inelastic electron-boundary scattering.
The Low Temperature Physics Conference is an international event held every three years, under the auspices of the IUPAP through its Commission C5 on Low Temperature Physics. The aim of these conferences is to exchange information and views among the members of the international scientific community in the general field of Low Temperature Physics. It is a tradition that LT offers updates on the various topics, provided by the highest representatives of the field, as well as oral and poster contributions in the different areas. As usual the conference covers five subtopics:Quantum fluids and solids Superconductivity Cryogenic techniques and applications Magnetism and quantum phase transitions Quantum transport and quantum information in condensed matter
Gothenburg is situated in the center of Scandinavia, on the Swedish West Coast, and is easily accessed by air. The city’s two universities – Chalmers University of Technology and University of Gothenburg – both have a long tradition in low temperature physics research, particularly superconductivity and quantum transport.
We study Josephson junctions with weak links consisting of two parallel disordered arms with magnetic properties: ferromagnetic, half-metallic, or normal with magnetic impurities. In the case of long links, the Josephson effect is dominated by mesoscopic fluctuations. In this regime, the system realizes a phi_0 junction with sample-specific phi_0 and critical current. Cooper pair splitting between the two arms plays a major role and leads to 2*Phi_0 periodicity of the current as a function of flux between the arms. We calculate the current and its flux and polarization dependence for the three types of magnetic links.
Book of abstracts
We consider ballistic SQUIDs with spin filtering inside half-metallic ferromagnetic arms. A singlet Cooper pair cannot pass through an arm in this case, so the Josephson current is entirely due to the Cooper pair splitting, with two electrons going to different interferometer arms. In order to elucidate the mechanisms of Josephson transport due to split Cooper pairs, we assume the arms to be single-channel wires in the short-junction limit. Different geometries of the system (determined by the length of the arms and the phases acquired by quasiparticles during splitting between the arms) lead to qualitatively different behavior of the SQUID characteristics (the Andreev levels, the current-phase relation, and the critical Josephson current) as a function of two control parameters, the external magnetic flux and misorientation of the two spin filters. The current-phase relation can change its amplitudeandshape,inparticular,turningtoaπ junctionformoracquiringadditionalzerocrossings.Thecritical current can become a nonmonotonic function of the misorientation of the spin filters and the magnetic flux (on half of period). Periodicity with respect to the magnetic flux is doubled, in comparison to conventional SQUIDs.
Superconducting properties of metallic nanowires can be entirely different from those of bulk superconductors because of the dominating role played by thermal and quantum fluctuations of the order parameter. For superconducting channels with diameters below ∼ 50 nm fluctuations of the phase of the complex order parameter - the phase slippage - lead to non-zero resistance below the critical temperature. Fluctuations of the modulus of the complex order parameter broaden the gap edge of the quasiparticle energy spectrum and modify the density of states. In extreme case of very narrow channels imbedded in high-impedance environment (which fix the charge and, hence, enable strong fluctuations of the quantum-conjugated variable, the phase) the superconductor can be driven to insulating state – the Coulomb blockade. We review recent experimental activities in the field demonstrating rather unusual phenomena.
The problem of designing stabilizing resonator (SR) for a 4-mm wavelengths range coaxial magnetron with low level of output power has been considered. The recommendations for choosen the coaxial resonator external to internal diameter relations depending on technical project requirements are developed.