Chairs
Professor Lesley Cohen, Imperial College London, UK
Professor Lesley Cohen, Imperial College London, UK
Professor Lesley Cohen is a professor of solid state physics studying the fundamental behaviour of materials and devices with unusual electronic, optical, superconducting or magnetic properties for a variety of applications including solid state efficient and environmentally friendly magnetic refrigeration. Over a number of years her group has developed a suite of characterisation tools that have enabled unique insight into the behaviour of materials at low temperatures and high magnetic fields. She has published over 350 journal publications in her areas of interest.
09:05-09:30
Robust superconductivity coexisting with ferromagnetism display unusual behaviour
Dr Jagadeesh S Moodera, Massachusetts Institute of Technology, USA
Abstract
Proximity coupling across superconductor-ferromagnet bilayers can give rise to the triplet component of the superconducting condensate. Superconductivity and ferromagnetism have been reported to coexist in a Ni/Bi bilayer system. Thus spin polarised triplet supercurrent in ferromagnetic-superconducting Josephson junctions can be expected. The Moodera group has investigated the complex and rich behaviour of this phenomenon in bilayers of Ni/Ga and Ni/Bi systems, including Josephson and quasiparticle tunnelling. Ni/Ga as well as Ni/Bi bilayer systems show unusual superconductivity, with high Tc that can co-exist with ferromagnetism. Tunnelling spectroscopy studies at low temperatures show the presence of three superconducting energy gaps in the bilayers, attributable to surface, interface and bulk states within the bilayers. Ni layers, ranging from 0.8 to 6nm thick, confirmed to be ferromagnetic by the magnetisation studies while spin polarised tunnelling studies revealed that the tunnelling electrons coming from the Ni surface were spin polarised and simultaneously displayed superconducting gap, supporting the co-existence of SC and FM. The interplay of SC and FM with the presence of spin polarised carriers in such bilayer system could be a strong case for triplet pairing. In addition, the observed Josephson current could be spin polarised. Interestingly, the superconductivity in the Ni/Bi bilayer is expected to be topological. The occurrence of zero bias conductance may reflect odd-frequency symmetry in the superconducting condensate, supporting the presence of a non-zero component associated with triplet pair superconductivity insensitive to disorder. Jagadeesh Moodera will present this ongoing work leaving it open for discussion. This work has been done in collaboration with Madison Sutula, Sebastian Bergeret, Jia Song, Valeria Lauter and Niladri Banerjee.
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Dr Jagadeesh S Moodera, Massachusetts Institute of Technology, USA
Dr Jagadeesh S Moodera, Massachusetts Institute of Technology, USA
Dr Jagadeesh Moodera is a senior research scientist and group leader at the physics department at MIT, USA. Jagadeesh is also a Distinguished Visiting Professor at the IQC, University of Waterloo; a Visiting Professor at the Applied Physics Department, Technical University of Eindhoven; a Distinguished Institute Professor at IIT Madras; and a Distinguished Foreign Scientist at NPL, Delhi. Jagadeesh has served on the Board of External Experts for national research programs in France, Holland, England and Ireland and has been elected a Fellow of the American Physical Society. He is also the recipient of several awards: IBM and TDK Research Awards, and the Oliver E. Buckley Condensed Matter Prize from the American Physical Society. Jagadeesh’s research interest lies in: 1) manipulating electron spin in solids-spin tunnelling, spin filtering and interfacial exchange coupling; 2) molecular spintronics: towards molecular-scale spin memory; 3) ferromagnet/superconductor heterostructure towards superconducting spintronics; 4) quantum transport in topological driven systems and heterostructures: atomic scale interface exchange phenomena; atomically resolved interface chemical/physical/magnetic studies; electrical transport; and 5) the search for Majorana bound states in unconventional superconductors, and interactions.
09:45-10:15
Transport properties of topological superconducting hybrid structures
Dr Cecilia Holmqvist, Linnaeus University, Sweden
Abstract
Dirac materials with strong spin-orbit interaction have been shown to generate large surface spin accumulations in response to applied currents. Such materials have, in addition, been demonstrated to exert spin-orbit torques on adjacent ferromagnetic structures. This magnetoelectric effect in these materials is strong due to the efficient spin-momentum locking. In heterostructures consisting of superconductors and three-dimensional superconductors, this spin-momentum locking leads to an induced unconventional superconductivity that may be useful for superconducting spintronics. Here, Cecilia Holmqvist investigates theoretically the quantum transport properties of a ballistic junction consisting of two topological superconductors coupled over a quantum dot that is coupled to a ferromagnet. The spin-orbit torques acting on the ferromagnet are examined and are shown to depend strongly on the magnetisation direction relative to the current direction.
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Dr Cecilia Holmqvist, Linnaeus University, Sweden
Dr Cecilia Holmqvist, Linnaeus University, Sweden
Cecilia Holmqvist is a postdoctoral research fellow at Linnaeus University, Sweden. She received her PhD at Chalmers University of Technology, Sweden, and subsequently was a postdoc at Konstanz University, Germany, and at the Norwegian University of Science and Technology, Norway. Her research interests include non-equilibrium charge and spin transport as well as noise in superconducting hybrid structures, in particular how Andreev states may interact with the dynamics of a nanomagnet. Her research interests also include spin-orbit torques and magnetisation dynamics generated by materials with strong spin-orbit coupling such as normal metals and topological insulators, and spin transport carried by classical spin-wave dynamics, such as spin superfluidity, in ferromagnets and antiferromagnets.
11:00-11:30
Magnetic moment manipulation by a superconducting current in Josephson junctions
Professor Alexander Buzdin, University of Bordeaux, France
Abstract
Recently several mechanisms realising the direct coupling between magnetic moment and Josephson current in S/F/S junctions have been proposed. In such junctions, the ac Josephson effect may generate a magnetic precession providing then a feedback to the current. Magnetic dynamics results in several anomalies of current-phase relations (second harmonic, dissipative current) which are strongly enhanced near the ferromagnetic resonance frequency. The simulations of magnetic moment dynamics show that by applying an electric current pulse, it may be possible to realise the full magnetisation reversal which is quite important for the elaboration of superconducting spintronic devices with low dissipation.
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Professor Alexander Buzdin, University of Bordeaux, France
Professor Alexander Buzdin, University of Bordeaux, France
Alexander Buzdin is a full professor at the University of Bordeaux in France; since 2004 he has been a senior member of the prestigious Institut Universitaire de France, where he holds the Chair “Physics of Superconductivity”. This year Alexander is the Liverhulme Trust professor at the Material Science Department of Cambridge University. Alexander graduated from Moscow State University and then habilitated in 1986. He worked under the supervision of the Nobel Prize winner Alexey Abrikosov at the Institute for High Pressure Physics of Russian Academy of Science and Argonne National Laboratory. Alexander is the author of more than 250 articles on superconductivity, magnetism and nanophysics. He received the Holweck Medal and Prize in 2013, a joint award by the UK Institute of Physics and the French Physical Society, for his pioneering theoretical studies of superconductor–ferromagnet multilayer systems.
11:45-12:15
Superconducting field-effect transistors go metal
Professor Francesco Giazotto, National Enterprise for Nanoscience and Nanotechnology, Italy
Abstract
In their original formulation of superconductivity, the London brothers predicted the exponential suppression of an electrostatic field inside a superconductor over the London penetration depth. Despite a few experiments indicating hints of perturbation induced by electrostatic fields, no clue has been provided so far on the possibility to manipulate conventional superconductors via field-effect. In this talk, Francesco Giazotto will show the evidence of full field-effect control of the supercurrent in all-metallic transistors made of different BCS superconducting films. At a low temperature, the field-effect transistors (FETs) show a monotonic decay of the critical current under increasing electrostatic field up to total quenching for gate voltage values as large as ±40V in titanium-based devices. A similar behaviour, though less pronounced, was observed in aluminum FETs. In addition, Francesco will report on the realisation of Ti-based Dayem bridge Josephson field-effect transistors. The latter show full suppression of IC for gate voltages as low as ±8V. Finally, Francesco will show the behaviour of mesoscopic superconductor-normal metal-superconductor Josephson field-effect transistors that will reveal the impact of electrostatic fields even on proximity metals thereby suggesting that the field effect is universal. Possible electronic and circuital schemes based on this all-metallic technology will be discussed.
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Professor Francesco Giazotto, National Enterprise for Nanoscience and Nanotechnology, Italy
Professor Francesco Giazotto, National Enterprise for Nanoscience and Nanotechnology, Italy
Francesco Giazotto graduated in Physics, and got a PhD in Physics (cum laude) in 2002 at Scuola Normale Superiore in Pisa. Since 2003 he is a senior scientist at NEST, Istituto Nanoscienze of CNR in Pisa. He was a visiting scientist for various periods from 2003 to 2008 at Aalto University in Helsinki (FI), and in 2011 at University Joseph Fourier in Grenoble (FR). Giazotto coordinates as Principal Investigator (PI) the activities of mesoscopic superconductivity, coherent caloritronics, electronic refrigeration, ultrasensitive quantum magnetometry, superconducting spintronics, and quantum transport in hybrid systems at ultralow temperatures at NEST laboratory. He has co-authored 145 articles in international journals, holds three patents on superconducting nanodevices, and has given 90 invited talks at national and international conferences. His papers have attracted more than 3900 citations and a 5-years h-index of 31 (Google Scholar). He is also referee of European projects and major international scientific journals. Since 2007 Francesco Giazotto has been PI in 10 projects (~4.5 M€), both European and national. For his research activities in the field of thermal transport at the nanoscale he has also achieved an ERC Consolidator Grant in 2013.