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Non-equilibrium superconductivity and spintronics

Scientific meeting

Location

Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell, Buckinghamshire, MK16 9JJ

Overview

Theo Murphy international scientific meeting organised by Professor Mark Blamire, Dr Chiara Ciccarelli, Professor Matthias Eschrig, Dr Jason Robinson and Professor Lesley Cohen

Visual spin. Credit: Irene Iorio

This meeting will bring together leading researchers in the fields of magnetism and superconductivity to explore new functionality in which spin, charge and superconducting phase coherence can work together. Their discoveries and predictions form the foundation for the field of superconducting spintronics which could eventually be developed as a replacement for large-scale semiconductor-based logic and memory.

The schedule of talks and speaker biographies are available below. Speaker abstracts will be available closer to the meeting. Recorded audio of the presentations will be available on this page after the meeting has taken place. Meeting papers will be published in a future issue of Philosophical Transactions A.

Poster session

There will be a poster session at 17:00 on Monday 25 February 2019. If you would like to apply to present a poster please submit your title, proposed abstract (not more than 200 words and in third person), author list, name of the proposed presenter and authors' institutions to the Scientific Programmes team no later than Monday 14 January 2019. Please include the text "Superconducting spintronics: poster abstract" in the subject heading. Please note that places are limited and are selected at the scientific organisers' discretion. Poster abstracts will only be considered if the presenter is registered to attend the meeting.

Attending this event

This is a residential conference, which allows for increased discussion and networking.

  • Free to attend
  • Advance registration essential
  • Catering and accommodation available to purchase during registration

Enquiries: contact the Scientific Programmes team

Event organisers

Select an organiser for more information

Schedule of talks

25 February

09:00-12:30

Session 1

4 talks Show detail Hide detail

Chairs

Professor Lesley Cohen, Imperial College London, UK

09:05-09:30 Towards interfacial exchange field-driven superconducting spintronics

Dr Jagadeesh S Moodera, Massachusetts Institute of Technology, USA

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09:45-10:15 Non-equilibrium charge and spin transport in topological insulator Josephson junctions

Dr Cecilia Holmqvist, Linnaeus University, Sweden

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10:30-11:00 Coffee

11:00-11:30 Magnetic moment manipulation by a superconducting current in Josephson junctions

Professor Alexander Buzdin, University of Bordeaux, France

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11:45-12:15

Professor Francesco Giazotto, National Enterprise for Nanoscience and Nanotechnolgy, Italy

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12:30-13:30

Lunch

13:30-17:00

Session 2

4 talks Show detail Hide detail

Chairs

Professor Matthias Eschrig, Royal Holloway, University of London, UK

13:30-12:00 Voltage-control over a high-field superconducting transition and the superconducting exchange interaction

Professor Jacob Linder, Norwegian University of Science and Technology, Norway

Abstract

Jacob Linder’s group predicts two interesting phenomena related to superconductivity in hybrid structures driven out of equilibrium by application of an electric voltage. Firstly, they theoretically demonstrate that superconductivity in thin films can be stabilised in high magnetic fields if the superconductor is driven out of equilibrium by a voltage bias. For realistic material parameters and temperatures, they show that superconductivity is restored in fields many times larger than the Chandrasekhar–Clogston limit. After motivating the effect analytically, they present rigorous numerical calculations to corroborate the findings, and discuss concrete experimental signatures. Secondly, Linder discusses how the magnetic exchange interaction in a spin-valve is influenced by non-equilibrium superconductivity. Linder shows that the sign of the exchange interaction in a spin-valve, determining whether a parallel or antiparallel magnetic configuration is favoured, can be controlled via an electric voltage. This occurs due to an interplay between a non-equilibrium quasiparticle distribution and the presence of spin-polarized Cooper pairs. These findings may be of relevance for spin-based superconducting devices which in practice most likely have to be operated precisely by non-equilibrium effects.

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14:15-14:45 Comparison of the spin-transfer torque mechanisms in three terminal spin-torque-oscillators

Dr Emilie Jué, National Institute of Standards and Technology, USA

Abstract

The spin transfer torque is one of the most active field of spintronics due to its potential for use in memory and logic applications. This control can be achieved via a spin polarised current with the mechanism of spin-filtering torque (SFT) or through a pure spin current via the mechanism of spin-orbit torque (SOT). Over the past several years, SOT has gained increased attention due to the new possibilities that it offers for data storage applications. However, the quantification and comparison of both mechanisms’ efficiencies remains uncertain, due to the uncertainty in material parameters needed to quantify the torque. In this work, researchers at NIST compared for the first time the SFT and SOT efficiencies acting on the same nanomagnetic element. To do so, they created 3-terminal spin-torque oscillators (STO) composed of spin-valves (SV) patterned on top of Pt nanowires. The devices are excited either by SFT or by SOT depending on whether the current is applied through the SV or through the Pt wire. By comparing the magnetization dynamics obtained with the different STT mechanisms, they quantify the relative efficiencies of the SOT and SFT in the system as a function of the dimensions of the SV and Pt nanowires.

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15:00-15:30 Tea

15:30-16:00 Ferromagnetic resonance studies of ferromagnets and superconductors

Dr Chiara Ciccarelli, University of Cambridge, UK

Abstract

Ferromagnetic resonance is a powerful method to extract information on the magnetic torques, spin damping and magnetic anisotropies. In Chiara Ciccarelli’s group ferromagnetic resonance methods are applied to quantitatively evaluate the spin torques in asymmetric ferromagnets, magnetic insulators and synthetic antiferromagnets. The focus of this talk will be on some recent work where spin pumping experiments are conducted on HM/SC/FM and SC/FM structures (SC=niobium, HM=platinum and FM=permalloy). Ferromagnetic resonance in the permalloy is excited via a waveguide and the damping measured through the superconducting transition temperature of niobium. These results show that while in the SC/FM structures spin pumping is suppressed when the niobium turns superconducting, in the HM/SC/FM structures the presence of platinum leads to an enhanced spin transfer through superconducting niobium with respect to its normal state and even with respect to bare platinum.

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16:15-16:45 Anomalous Meissner effect in superconductor-ferromagnet proximity systems

Dr Machiel Flokstra, University of St Andrews, UK

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17:00-18:00 Poster session

26 February

09:00-12:30

Session 3

4 talks Show detail Hide detail

Chairs

Dr Hidekazu Kurebayashi, University College London, UK

09:00-09:30 Non-equilibrium effects in superconducting systems with spin-dependent fields

Dr Sebastian Bergeret Material Physics Center (CFM-CSIC), Spain

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09:45-10:15 Thermoelectric effects in superconductor-ferromagnet structures

Professor Detlef Beckmann, Karlsruhe Institute of Technology, Germany

Abstract

Detlef Beckmann covers the experimental observation of spin-dependent thermoelectric effects in superconductor-ferromagnet tunnel junctions in high magnetic fields. The thermoelectric signals are due to a spin-dependent lifting of particle-hole symmetry on the energy scale of the superconducting gap. Due to the small energy scale, the thermoelectric effects can be quite large, and a maximum Seebeck coefficient of about 100 µV/K can be inferred from the data. The thermoelectric signals can be further enhanced by an exchange splitting induced by the proximity effect with a ferromagnetic insulator. The results directly prove the coupling of spin and heat transport in high-field superconductors, which also leads to nonlocal thermoelectric effects in multiterminal devices where several ferromagnetic wires are attached to a single superconducting wire via tunnel junctions. In these structures, heating one of the ferromagnetic wires leads to a nonlocal thermoelectric current in a remote wire, over distances of the order of 10 µm.

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10:30-11:00 Coffee

11:00-11:30 Generation of pure superconducting spin current in magnetic heterostructures via non-locally induced magnetism

Dr Xavier Montiel, Royal Holloway, University of London, UK

Abstract

The researchers of RHUL propose a mechanism for the generation of pure superconducting spin-current carried by equal-spin triplet Cooper pairs in a superconductor (S) sandwiched between a ferromagnet (F) and a normal metal (Nso) with intrinsic spin-orbit coupling. They show that in the presence of Landau Fermi-liquid interactions the superconducting proximity effect can induce non-locally a ferromagnetic exchange field in the normal layer, which disappears above the superconducting transition temperature of the structure. The internal Landau Fermi-liquid exchange field leads to the onset of a spin supercurrent associated with the generation of long-range spin-triplet superconducting correlations in the trilayer. They demonstrate that the magnitude of the spin supercurrent as well as the induced magnetic order in the Nso layer depends critically on the superconducting proximity effect between the S layer and the F and Nso layers and the magnitude of the relevant Landau Fermi-liquid interaction parameter. Their results demonstrate the crucial role of Landau Fermi-liquid interaction in combination with spin-orbit coupling for the creation of spin supercurrent in superconducting spintronics.

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11:45-12:15 Chiral spin interactions mediated by a supercurrent

Dr Irina Bobkova, Institute of Solid State Physics of RAS and Moscow Institute of Physics and Technology, Russia

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12:30-13:30

Lunch

13:30-17:00

Session 4

4 talks Show detail Hide detail

Chairs

Dr Jason Robinson, University of Cambridge UK

13:30-14:00

Dr Joerg Wunderlich, Hitachi Cambridge Lab, UK, and Institute of Physics of the Academy of Science, Czech Republic

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14:15-14:45 Phase-controllable Josephson junctions and cryogenic memory

Professor Norman Birge, Michigan State University, USA

Abstract

Josephson junctions containing ferromagnetic (F) materials are being developed for use in cryogenic random access memory. In principle, either the critical current amplitude or the ground-state phase difference across the junction could be used to store information. In the Northrop Grumman JMRAM memory architecture, the ferromagnetic junction acts as a passive phase shifter in a SQUID loop that also contains two SIS junctions. Phase control has now been demonstrated in two kinds of Josephson junctions: in a simple spin-valve device containing two ferromagnetic layers and in a more complex multi-layer device that carries spin-triplet supercurrent. In both types of devices, the ground-state phase difference can be controllably switched between 0 and π by reversing the magnetisation direction of one of the magnetic layers in the device. The physical mechanism by which the ground-state phase difference changes, however, is different in the two types of devices. Both types of devices require further optimisation to be suitable for large-scale superconducting memory arrays. This talk will review the physics underlying the behaviour of both types of ferromagnetic Josephson junctions, and discuss progress in optimising devices for use in cryogenic memory.

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15:00-15:30 Tea

15:30-16:00 Surface superconducting property proved by pure spin current

Professor Takashi Kimura, Kyushu University, Japan

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16:15-17:00 Superconducting quantum-classical information processing systems

Dr Oleg Mukhanov, HYPRES Inc, USA

Abstract

Superconducting rapid single flux quantum (RSFQ) logic is now used in radio frequency signal digital receivers. Sophisticated superconducting SFQ-based digital processors and memories are being developed for the next generation energy efficient data centres. Recently, RSFQ and its energy-efficient successor logics were used to realize classical control for quantum processors. Traditionally, control operations are performed at room temperature leading to scalability limitations and long latency in quantum operations. For scalable low-latency qubit control, the classical electronics should located as close to quantum chips as possible. Superconducting SFQ circuits proximally located to the quantum processor can be the technology of choice due to its low power (10-21 Joule to per switching at 20 mK). They can be engineered to produce the minimal back action to qubits. The ability to operate at very high speed (tens of gigahertz clock) opens a way for digitizing and fast processing qubit output data for error correction and generation of qubit control signals. Furthermore, hybrid systems integrating together the quantum and classical processing hardware units are envisioned to enable various application algorithms which typically combine quantum and classical algorithmic modules. The implementation of scalable quantum-classical 3D integrated system extending across multiple temperature stages will be discussed.

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Non-equilibrium superconductivity and spintronics

Theo Murphy international scientific meeting organised by Professor Mark Blamire, Dr Chiara Ciccarelli, Professor Matthias Eschrig, Dr Jason Robinson and Professor Lesley Cohen

Kavli Royal Society Centre, Chicheley Hall Newport Pagnell Buckinghamshire MK16 9JJ
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