Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F3: Superconducting SpintronicsInvited
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Sponsoring Units: GMAG DCMP Chair: Hans Nembach, National Institute of Standards and Technology Room: Ballroom III |
Tuesday, March 15, 2016 11:15AM - 11:51AM |
F3.00001: The road to superconducting spintronics Invited Speaker: Matthias Eschrig Energy efficient computing has become a major challenge, with the increasing importance of large data centres across the world, which already today have a power consumption comparable to that of Spain, with steeply increasing trend. Superconducting computing is progressively becoming an alternative for large-scale applications, with the costs for cooling being largely outweighed by the gain in energy efficiency. The combination of superconductivity and spintronics - ``superspintronics'' - has the potential and flexibility to develop into such a green technology. This young field is based on the observation that new phenomena emerge at interfaces between superconducting and other, competing, phases. The past 15 years have seen a series of pivotal predictions and experimental discoveries relating to the interplay between superconductivity and ferromagnetism. The building blocks of superspintronics are equal-spin Cooper pairs, which are generated at the interface between superconducting and a ferromagnetic materials in the presence of non-collinear magnetism. Such novel, spin-polarised Cooper pairs carry spin-supercurrents in ferromagnets and thus contribute to spin-transport and spin-control. Geometric Berry phases appear during the singlet-triplet conversion process in structures with non-coplanar magnetisation, enhancing functionality of devices, and non-locality introduced by superconducting order leads to long-range effects. With the successful generation and control of equal-spin Cooper pairs the hitherto notorious incompatibility of superconductivity and ferromagnetism has been not only overcome, but turned synergistic. I will discuss these developments and their extraordinary potential. I also will present open questions posed by recent experiments and point out implications for theory. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:27PM |
F3.00002: Nanoscale memory elements based on the superconductor-ferromagnet proximity effect and spin-transfer torque magnetization switching Invited Speaker: Burm Baek Superconducting-ferromagnetic hybrid devices have potential for a practical memory technology compatible with superconducting logic circuits and may help realize energy-efficient, high-performance superconducting computers. We have developed Josephson junction devices with pseudo-spin-valve barriers \footnote{B. Baek et al., Nat. Commun. 5, 3888, (2014).}. We observed changes in Josephson critical current depending on the magnetization state of the barrier (parallel or anti-parallel) through the superconductor-ferromagnet proximity effect. This effect persists to nanoscale devices in contrast to the remanent field effect. In nanopillar devices \footnote{B. Baek et al., Phys. Rev. Appl. 3, 011001 (2015).}, the magnetization states of the pseudo-spin-valve barriers could also be switched with applied bias currents at 4 K, which is consistent with the spin-transfer torque effect in analogous room-temperature spin valve devices. These results demonstrate devices that combine major superconducting and spintronic effects for scalable read and write of memory states, respectively. Further challenges and proposals towards practical devices will also be discussed.\\ \\In collaboration with: William Rippard, NIST – Boulder, Matthew Pufall, NIST – Boulder, Stephen Russek, NIST-Boulder, Michael Schneider, NIST – Boulder, Samuel Benz, NIST – Boulder, Horst Rogalla, NIST-Boulder, Paul Dresselhaus, NIST - Boulder [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 1:03PM |
F3.00003: Spin-polarized superconductivity for spintronics Invited Speaker: Jason Robinson The feasibility of superconducting spintronics depends on the spin sensitivity of ferromagnets to the spin of equal-spin triplet Cooper pairs (1). Such pairs are generated at superconductor(S) / ferromagnet(F) interfaces in which certain forms of magnetic inhomogeneity (2,3) are present. In this talk I will introduce the topic of the triplet proximity effect in S-F heterostructures and will discuss my group's recent progress, which includes: spin-selectivity of triplet Cooper pairs in F-S-F superconducting spin-valves (4) and evidence for the formation of a spin-polarized superconducting densities of state in an s-wave superconductor proximity coupled to a magnetically inhomogeneous antiferromagnet (5). \begin{enumerate} \item 1. J Linder and JWA Robinson. \textit{Nature Physics} 11, 307 (2015). \item 2. JWA Robinson, JDS Witt, MG Blamire. \textit{Science} 329, 59 (2010). \item 3. C Klose \textit{et al.,} \textit{Phys. Rev. Lett. }108, 127002 (2012). \item 4. N Banerjee, C Smiet, R Smits, A Ozaeta, F Bergeret, M Blamire, JWA Robinson, \textit{Nature Comm.} 5, 3048 (2014). \item 5. A Di Bernardo, S Diesch, Y Gu, J Linder, G Divitini, C Ducati, E Scheer, MG Blamire, JWA Robinson, \textit{Nature Comm.} 6, 8053 (2015). \end{enumerate} [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:39PM |
F3.00004: Quasiparticle-mediated spin Hall effect in a superconductor Invited Speaker: Taro Wakamura Superconductivity often brings novel phenomena to spintronics. According to theoretical predictions, superconductivity may enhance the spin Hall effect (SHE) due to the increase in the resistance of superconducting quasiparticles which mediate spin transport in superconductors. In this work, we show a first experimental observation of quasiparticle-mediated SHE in a superconducting NbN, which exhibits an enormous enhancement below the superconducting critical temperature ($T_{\mathrm{C}}=$10 K). We fabricated a lateral device structure composed of Py (NiFe) and NbN wires bridged by a nonmagnetic Cu wire. A pure spin current is generated in the Cu bridge by a spin injection current ($I)$ between the Py and the Cu, and absorbed into the NbN wire. The absorbed spin currents are converted into charge currents via the inverse SHE, thereby generating the inverse SH voltage ($V_{\mathrm{ISHE}})$. When NbN is in the normal state at 20 K (\textgreater $T_{\mathrm{C}})$, inverse SH signals $\Delta R_{\mathrm{ISHE}}$ ($R_{\mathrm{ISHE}}\equiv V_{\mathrm{ISHE}}$/$I)$ are independent of$ I$. However, at 3 K (\textless $T_{\mathrm{C}})$, as $I$ decreases $\Delta R_{\mathrm{ISHE}}$ dramatically increases, and when $I=$0.01 $\mu $A, the signal becomes more than 2000 times greater than that in the normal state. Our experimental demonstration shows a great potentiality of superconductors for spintronics and its future applications. [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 2:15PM |
F3.00005: Cryogenic Memories based on Spin-Singlet and Spin-Triplet Ferromagnetic Josephson Junctions Invited Speaker: Eric Gingrich The last several decades have seen an explosion in the use and size of computers for scientific applications. The US Department of Energy has set an ExaScale computing goal for high performance computing that is projected to be unattainable by current CMOS computing designs [1]. This has led to a renewed interest in superconducting computing as a means of beating these projections. One of the primary requirements of this thrust is the development of an efficient cryogenic memory. Estimates of power consumption of early Rapid Single Flux Quantum (RSFQ) memory designs are on the order of MW, far too steep for any real application [1]. Therefore, other memory concepts are required. S/F/S Josephson Junctions, a class of device in which two superconductors (S) are separated by one or more ferromagnetic layers (F) has shown promise as a memory element. Several different systems have been proposed utilizing either the spin-singlet or spin-triplet superconducting states [2]. This talk will discuss the concepts underpinning these devices, and the recent work done to demonstrate their feasibility. [1] - Energy-Efficient Superconducting Computing - Power Budgets and Requirements, D. Scott Holmes, Andrew L. Ripple, Marc A. Manheimer, IEEE Trans. Appl. Supercon., Vol 23, No. 3, June 2013 [2] - B. M. Niedzielski et al., ``Use of Pd-Fe and Ni-Fe-Nb as soft magnetic layers in ferromagnetic Josephson junctions for nonvolatile cryogenic memory,'' IEEE Trans. Appl. Supercond., vol. 24, no. 4, Aug. 2014, Art. ID. 1800307. [Preview Abstract] |
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