Cooper pair splitting in diffusive magnetic SQUIDs
We analyze a trade-o between thermal activation (TA) and quantum tunneling in the problem of supercurrent decay in superconducting junctions with highly transparent barriers. In such systems -- unlike in conventional tunnel junctions -- the supercurrent decay is essentially influenced by low energy Andreev levels forming an intrinsic quantum dissipative environment for the Josephson particle. We evaluate the temperature dependent supercurrent decay rate and elucidate a variety of di erent regimes for such a decay. We demonstrate that no classical-to-quantum crossover exists in the limit of fully transparent barriers, in which case quantum tunneling always prevails over TA.
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.
Book of abstracts
We present a detailed theoretical description of quantum coherent electron transport in voltage-biased crosslike Andreev interferometers.Making use of the charge conjugation symmetry encoded in the quasiclassical formalism, we elucidate a crucial role played by geometric and electron-hole asymmetries in these structures. We argue that a nonvanishing Aharonov-Bohm-like contribution to the current IS flowing in the superconducting contour may develop only in geometrically asymmetric interferometers making their behavior qualitatively different from that of symmetric devices. The current I_N in the normal contour—along with I_S—is found to be sensitive to phase-coherent effects thereby also acquiring a 2π-periodic dependence on the Josephson phase. In asymmetric structures this current develops an odd-in-phase contribution originating from electron-hole asymmetry. We demonstrate that both phase-dependent currents I_S and I_N can be controlled and manipulated by tuning the applied voltage, temperature, and system topology, thus rendering Andreev interferometers particularly important for future applications in modern electronics.
The quantum behavior of superconducting nanowires may essentially depend on the employed experimental setup. Here we investigate a setup that enables passing equilibrium supercurrent across an arbitrary segment of the wire without restricting fluctuations of its superconducting phase. The low temperature physics of the system is determined by a combined effect of collective soundlike plasma excitations and quantum phase slips. At T=0 the wire exhibits two quantum phase transitions, both being controlled by the dimensionless wire impedance g. While thicker wires with g>16 stay superconducting, in the thinnest wires with g<2 the supercurrent is totally destroyed by quantum fluctuations. The intermediate phase 2<g>16 is characterized by two different correlation lengths demonstrating superconductinglike behavior at shorter scales combined with vanishing superconducting response in the long scale limit.
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 dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
By using superconducting quantum interference device (SQUID) magnetometry, we investigated anisotropic high-field (H less than or similar to 7T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d(c) similar or equal to 1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5-2T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. In addition, the inhomogeneous nanoisland FeNi films can possess spontaneous ordering of toroidal moments, which can be either of orbital or spin origin. The system with toroidal inhomogeneity can lead to anomalously strong diamagnetic-like response. The observed magnetization response is determined by the interplay between the paramagnetic-and diamagnetic-like contributions.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.