Spin Transport in Diffusive Superconductors

We employ the Keldysh formalism in the quasiclassical approximation to study transport in a diffusive superconductor. The resulting 4x4 transport equations describe the flow of charge and energy as well as the corresponding flow of spin and spin energy. Spin-flip scattering due to magnetic impurities is included. We find that the spin-flip length is renormalized in the superconducting case and propose an experimental system to measure the spin-accumulation in a superconductor.Comment: 5 pages, 2 figure

Elementary Charge Transfer Processes in a Superconductor-Ferromagnet Entangler

We study the production of spatially separated entangled electrons in ferromagnetic leads from Cooper pairs in a superconducting lead. We give a complete description of the elementary charge transfer processes, i) transfer of Cooper pairs out of the superconductor by Andreev reflection and ii) distribution of the entangled quasiparticles among the ferromagnetic leads, in terms of their statistics. The probabilities that entangled electrons flow into spatially separated leads are completely determined by experimentally measurable conductances and polarizations. Finally, we investigate how currents, noise and cross correlations are affected by transport of entangled electrons.Comment: 5 pages. Rewritten manuscript with 2 new figures. Title changed from v

Circuit theory of crossed Andreev reflection

We consider transport in a three terminal device attached to one superconducting and two normal metal terminals, using the circuit theory of mesoscopic superconductivity. We compute the nonlocal conductance of the current out of the first normal metal terminal in response to a bias voltage between the second normal metal terminal and the superconducting terminal. The nonlocal conductance is given by competing contributions from crossed Andreev reflection and electron cotunneling, and we determine the contribution from each process. The nonlocal conductance vanishes when there is no resistance between the superconducting terminal and the device, in agreement with previous theoretical work. Electron cotunneling dominates when there is a finite resistance between the device and the superconducting reservoir. Decoherence is taken into account, and the characteristic timescale is the particle dwell time. This gives rise to an effective Thouless energy. Both the conductance due to crossed Andreev reflection and electron cotunneling depend strongly on the Thouless energy. We suggest to experimentally determine independently the conductance due to crossed Andreev reflection and electron cotunneling in measurement of both energy and charge flow into one normal metal terminal in response to a bias voltage between the other normal metal terminal and the superconductor.Comment: v2: Published version with minor changes, 12 pages and 9 figure

Femtosecond-pulse-train ionization of Rydberg wave packets

We calculate, based on first-order perturbation theory, the total and differential ionization probabilities from a dynamic periodic Rydberg wave packet of a given n-shell exposed to a train of femtosecond laser pulses. The total probability is shown to depend crucially on the laser repetition rate: For certain frequencies the ionization probability vanishes, while for others it becomes very large. The origin of this effect is the strong dependence of the ionization probability on the Stark quantum number. Correspondingly, the angular electronic distribution also changes significantly with the increasing number of pulses for certain repetition rates.publishedVersio

Full counting statistics of crossed Andreev reflection

We calculate the full transport counting statistics in a three-terminal tunnel device with one superconducting source and two normal-metal or ferromagnet drains. We obtain the transport probability distribution from direct Andreev reflection, crossed Andreev reflection, and electron transfer which reveals how these processes' statistics are determined by the device conductances. The cross-correlation noise is a result of competing contributions from crossed Andreev reflection and electron transfer, as well as antibunching due to the Pauli exclusion principle. For spin-active tunnel barriers that spin polarize the electron flow, crossed Andreev reflection and electron transfer statistics exhibit different dependencies on the magnetization configuration, and can be controlled by relative magnetization directions and voltage bias

Mammals show faster recovery from capture and tagging in human-disturbed landscapes

Wildlife tagging provides critical insights into animal movement ecology, physiology, and behavior amid global ecosystem changes. However, the stress induced by capture, handling, and tagging can impact post-release locomotion and activity and, consequently, the interpretation of study results. Here, we analyze post-tagging effects on 1585 individuals of 42 terrestrial mammal species using collar-collected GPS and accelerometer data. Species-specific displacements and overall dynamic body acceleration, as a proxy for activity, were assessed over 20 days post-release to quantify disturbance intensity, recovery duration, and speed. Differences were evaluated, considering species-specific traits and the human footprint of the study region. Over 70% of the analyzed species exhibited significant behavioral changes following collaring events. Herbivores traveled farther with variable activity reactions, while omnivores and carnivores were initially less active and mobile. Recovery duration proved brief, with alterations diminishing within 4–7 tracking days for most species. Herbivores, particularly males, showed quicker displacement recovery (4 days) but slower activity recovery (7 days). Individuals in high human footprint areas displayed faster recovery, indicating adaptation to human disturbance. Our findings emphasize the necessity of extending tracking periods beyond 1 week and particular caution in remote study areas or herbivore-focused research, specifically in smaller mammals

Coherent and Correlated Spin Transport in Nanoscale Superconductors

Motivated by the desire for better understanding of nanoelectronic systems, we theoretically study the conductance and noise characteristics of current flow between superconductors, ferromagnets, and normal-metals. Such nanostructures can reveal information about superconductor proximity effects, spin-relaxation processes, and spintronic effects with potential applications for different areas of mesoscopic physics. We employ the quasiclassical theory of superconductivity in the Keldysh formalism, and calculate the nonequilibrium transport of spin and charge using various approaches like the circuit theory of quantum transport and full counting statistics. For two of the studied structures, we have been able to compare our theory to experimental data and obtain good agreement. Transport and relaxation of spin polarized current in superconductors is governed by energy-dependent transport coefficients and spin-flip rates which are determined by quantum interference effects. We calculate the resulting temperature-dependent spin flow in ferromagnet-superconductor devices. Experimental data for spin accumulation and spin relaxation in a superconducting nanowire is in agreement with the theory, and allows for a spin-flip spectroscopy that determines the dominant mechanism for spin-flip relaxation in the studied samples. A ferromagnet precessing under resonance conditions can give rise to pure spin current injection into superconductors. We find that the absorbed spin current is measurable as a temperature dependent Gilbert damping, which we calculate and compare to experimental data. Crossed Andreev reflection denotes superconducting pairing of electrons flowing from different normal-metal or ferromagnet terminals into a superconductor. We calculate the nonlocal currents resulting from this process in competition with direct electron transport between the normal-metal terminals. We take dephasing into account, and study the nonlocal current when the types of contact in the system varies from e.g. ballistic conductors or tunnel barriers. In the tunneling case, we calculate the magnetization-dependent full counting statistics, which determines all noise properties including the cross-correlations that can resolve the contributions due to crossed Andreev reflection and direct electron transport. We evaluate the magnetization-dependent two-particle probability that the constituents of spin-entangled pairs from crossed Andreev reflection flow into different ferromagnetic contacts. This probability implies violation of a Bell inequality, and determines the performance of a superconductor-ferromagnet entangler

Clinical investigation for displaced proximal humeral fractures in the elderly: a randomized study of two surgical treatments: reverse total prosthetic replacement versus angular stable plate Philos (The DELPHI-trial)

Background Treatment for displaced proximal humeral fractures is still under debate. Few studies exist at the highest level of evidence. Although reversed total shoulder prosthesis has gained popularity and showed promising results in the treatment for proximal humeral fractures in the elderly patients, no randomized controlled trials exist to the authors’ knowledge. Methods/Design This study is a randomized semi-blinded controlled multicenter trial designed according to the Consort statement and the recommendations given by the Cochrane reviewers for proximal humeral fractures. The study will investigate whether a reversed total shoulder prosthetic replacement gain better functional outcome compared to open reduction and internal fixation using an angular stable plate in displaced three- and four parts proximal humeral fractures after two and five years follow-up. Participants are aged 65–85 admitted in seven different hospitals with a displaced proximal humeral fracture according to AO-OTA type 11-B2 or 11-C2. The intervention group is surgical treatment using a reversed total shoulder prosthesis (Delta X-tend) compared to open reduction and internal fixation with an angular stable plate (Philos) and thread cerclage in the control group. 60 patients will be randomized to each group. The primary outcome is shoulder function (Constant score). Secondary outcomes will be patient self-assessment form (Oxford shoulder score), a quality of life questionnaire (15D score) and resource implications (cost-effectiveness). Follow-ups take place at 3, 6, 12 and 24 months, and five years. The trial design is semi-blinded with blinded physiotherapists performing the functional testing of patients at all follow-ups. Randomization to treatment groups is electronic online, by independent supervisor (web-CRF). The recruitment of patients started at January 1.st 2013. Inclusion of 120 patients during three years is expected. Discussion This semiblinded trial include a high number of patients compared to existing randomized trials in this field. To our knowledge and according to ClinicalTrials.gov, this is the first study that compare these two treatments for a displaced proximal humeral fracture in elderly patients. This may provide important information to help the surgeon to decide the best treatment in the future. Trial registration number ClinicalTrials.gov Identifier: NCT0173706

Spin transport and magnetoresistance in ferromagnet/superconductor/ferromagnet spin valves

We consider spin transport and spin relaxation in superconductors using the quasiclassical theory of superconductivity. We include spin relaxation due to spin-orbit interaction as well as magnetic impurities, and show that the energy dependence of the spin-flip rate is different for these two mechanisms. In ferromagnetsuperconductor- ferromagnet systems made of Co and Al, interface resistances can be small compared to bulk resistances. This simplifies the description of transport in Co/Al/Co spin valves, for which we numerically calculate the temperature and Al length dependence of the magnetoresistance