No abstract
Spin imbalance is predicted to lead to suppression of superconductivity. We report phenomena manifesting this effect under spin-polarized quasiparticle currents in ferromagnetsuperconductor-ferromagnet single electron transistors. The measured superconducting gap as a function of magnetic field reveals a dramatic decrease when the magnetizations of the two leads are in opposite orientations. The effect of suppression increases with increasing voltage but decreases at elevated temperatures. The possible explanations for these dependences are given. This method may render it applicable to control superconductivity at low temperatures and low fields.PACS numbers: 74.25. Ha, 75.75.+a, 85.35.Gv The interplay between superconductivity and magnetism has been a topic of interest for many years. Of particular interest are recent experiments on ferromagnet/superconductor (FM/SC) junctions with high T C [1] in which a decrease of the supercurrent by nonequilibrium spin density was demonstrated. Furthermore, theoretical studies [2,3] also indicate that spin imbalance in a superconductor can lead to suppression of superconductivity. In a double tunnel junction containing a normal metal or a superconductor sandwiched between two ferromagnets, both injection of polarized current and spin accumulation are possible, and thus provide an ideal test ground for the theory. When the magnetic moments of the two ferromagnetic leads are in opposite orientations (referred to as the antiferromagnetic (AF) alignment), the difference in the number of majority and minority spins in the central electrode brings in a chemical potential difference. In a normal metal, this potential difference is superconductors δµ = P eV /2, where P is the polarization of the ferromagnetic leads and V is the voltage across the sample. In a superconductor, this difference gives rise to pair breaking, same as the Zeeman effect does to superconductivity in the paramagnetic limit. In this paper, we report the first direct observation of the superconducting gap suppression using Co/Al/Co (FM/SC/FM) double tunnel junctions. The effect can be turned on and off by manipulating the mutual orientations of the magnetic moment of the two Co leads. We further discuss some relevant time scales, including the spin relaxation time and the tunneling time, which set the criterion for spin accumulation in the superconductor.The inset of Fig. 1 shows an SEM picture of a measured sample and its biasing circuit. The samples were fabricated by standard electron-beam lithography techniques and by the shadow evaporation method. A thin native Al 2 O 3 layer between the Al island and the Co electrodes acted as a tunnel barrier. Aluminum is a good candidate to serve as the superconductor for this purpose, not just for its long spin lifetime [4] allowing the full range of spin effects to be studied, but also for its high quality native Al 2 O 3 barrier which was shown to have no spin-flip tunneling processes [5]. Our electron-gun deposited Al islands have a superconducting transition te...
Magnetoresistance (MR) in Co–Al–Co and Al–Co–Al double tunneling junctions has been studied at temperatures between 65 and 750 mK and in magnetic fields up to 3 T. The electrical resistance decreases with increasing temperature. In the low magnetic field region, the electrical resistance hysteresis behavior is attributed to a typical TMR for ferromagnetic Co and insulator Al2O3 elements. In the high magnetic field region, a sharp resistance variation roughly near 2.0 T for the Co–Al–Co system and 1.75 T for the Al–Co–Al system has been observed and is attributed to the electron tunneling effect. From the current–voltage and dI/dV characteristics, the superconductivity energy gap is roughly 0.5 meV in the Co–Al–Co system and roughly 0.3 meV in the Al–Co–Al system; and magnetic tunneling energy is roughly 0.01 meV in the Co–Al–Co system and roughly 0.06 meV in the Al–Co–Al system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.