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August 31, 2019
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Swimming upstream Flux flow reverses for lattice bosons in a magnetic field

first_img This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Copyright 2011 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Sebastian D. Huber in the Department of Condensed Matter Physics at Weizmann, working with Netanel H. Lindner at CalTech’s Institute for Quantum Information and Department of Physics, describes the obstacles encountered in conducting their research. “The Hall conductivity of continuum bosons is directly dictated by the density of particles,” says Huber. “Interesting lattice effects leading to a deviation from this elementary rule are only at work for strong inter-particle interactions. In short, the existence of holes is crucial to our work.” Citation: Swimming upstream: Flux flow reverses for lattice bosons in a magnetic field (2011, December 27) retrieved 18 August 2019 from https://phys.org/news/2011-12-upstream-flux-reverses-lattice-bosons.html Forces acting on a vortex. (a) The classical Magnus force due to the interaction of the velocity field of the vortex and the external flow vs acts perpendicular to vs. (b) Vortex motion leads to a change in the momentum of the system due to its phase singularity, which is perpendicular to its velocity vv. (c) Moving a vortex around a lattice site yields a Berry phase of 2πα = 2π(nb + p). Copyright © PNAS, doi: 10.1073/pnas.1110813108 (PhysOrg.com) — Matter in the subatomic realm is, well, a different matter. In the case of strongly correlated phases of matter, one of the most surprising findings has to do with a phenomenon known as the Hall response – an important theoretical and experimental tool for describing emergent charge carriers in strongly correlated systems, examples of which include high temperature superconductors and the quantum Hall effect. At Weizmann Institute of Science and California Institute of Technology, recent theoretical physics research into bosons interacting in a magnetic field has shown that, among other surprising effects, Hall conductivity – and therefore flux flow – undergo reversal. The scientists have concluded that their findings are immediately applicable to a wide range of phenomena in the realm of condensed matter physics. Concerning the surprising effects they found (e.g., sign reversal) of topological transitions between different integer values, Huber stresses that while it has been well-known since the discovery of the quantum Hall state that topology can have an important influence on solid state systems, there has recently been tremendous interest in topologically non-trivial states in the form of topological insulators. “However,” he adds, “all these systems are characterized by a gap to excitations in the bulk. Our results show that such topological transitions, and consequently the sign-reversals, are possible also in a gapless superfluid.”While these findings are new, they are actually based on a very old theorem by von Neumann and Wigner regarding level crossings. “So,” Huber concludes, “in a sense we only brought existing knowledge on the structure of energy levels into the fascinating new world of topology in condensed matter systems.”center_img Recognizing blood poisoning quickly Explore further While for fermions the band theory of solids together with the Pauli principle provides the notion of holes, for bosons they needed an interaction-driven Mott insulator – a material that should conduct electricity according to conventional band theories, but due to particle-particle interactions is an insulator when measured, particularly at low temperatures – for holes to arise. “Hence, our main challenge was to study a lattice effect in the presence of strong interactions.”Huber and Lindner addressed the question of the Hall conductivity by using concepts of topology like the Chern number and the effective magnetic monopoles which constitute sources of the Chern density. “While these concepts are well known,” Huber explains, “their application to gapless interacting systems is novel. The realization that gapless systems can also have topological transitions like the ones we found between different values of the Chern number, or equivalently, the Hall conductivity, is certainly an exciting new discovery. The actual question we resolved – the value of the Hall coefficient of lattice bosons – has been a longstanding problem motivated by high-temperature superconductivity. In this sense, our work contributes to a deeper understanding of lattice systems in general.”Huber describes the next steps being considered, given that their work has shown that sign reversals of the Hall conductivity are possible in clean systems with no disorder, as well as in a purely bosonic model. “In high-temperature superconductors such reversals are experimentally observed,” Huber notes. ”The common wisdom is that the underlying Fermi surface is undergoing a structural change due to a competing instability of strip-formation. Our work suggests that this might not be the only source of such sign-reversals and no fermionic mechanism needs to be invoked. As the exact nature of these systems is highly controversial, we plan to extend our work to be able to directly access this problem.” More information: Topological transitions for lattice bosons in a magnetic field, Published online before print November 22, PNAS December 13, 2011, vol. 108 no. 50, 19925-19930, doi: 10.1073/pnas.1110813108 Topological transitions in the Bose-Hubbard phase diagram. The Galilean invariant regime denotes the region where σxy is proportional to the particle density nb divided by the magnetic field strength B. Mott insulator lobes are indicated in gray. The yellow and green lines exhibit an emergent particle hole symmetry, where σxy = 0. They are divided into two types: (i) Lines emanating from the tip of the Mott lobe at integer boson filling where σxy has a smooth zero crossing (green). (ii) Transition lines (yellow), through which Bσxy exhibits integer jumps. The latter continue into the phase diagram, with σxy > 0, as indicated by the dashed lines. The blue region corresponds to regions where the Hall conductivity is negative. Copyright © PNAS, doi: 10.1073/pnas.1110813108last_img read more

August 10, 2019
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January 25 2016The third annual Here we see Zuni

first_imgJanuary 25, 2016The third annual Here we see Zuni Ishakawa teaching her class “Dying with Natural Dyes” outside in the silt-cast area below the Music Center.[photos and text by Sue Kirsch]Val Hilburgh with her “Hand Spindle” class in the Music Center.Mary Conti with some of her students of “Tapestry and Beyond” in the old bakery.Louise Hall and her student Chris with a gorgeous scarf made during “Nuno Felting” class.Tasha Miller Griffith teaching Felt Cuff and Beads.last_img

August 5, 2019
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LEGENDERRY BOOST AT BBC GOOD FOOD SHOW IN BELFAST

first_img LEGENDERRY BOOST AT BBC GOOD FOOD SHOW IN BELFAST LEGENDERRY Food producers and tourism ambassadors from Derry City and Strabane District Council (DCSDC) and Visit Derry rubbed shoulders with the culinary elite and celebrity chefs at the BBC Good Food Show’s first ever visit to Belfast as part of Northern Ireland Year of Food & Drink 2016 at the weekend.Showcasing the cream of local produce in conjunction with Tourism NI and Food NI at the three-day event held in Belfast Waterfront were Doneybrewer Butter (Eglinton) with their sea-salted butter and, Tamnagh Foods (Park) with their Dart Mountain cheese brand and chutneys whose attendance was supported by DCSDC.Huge crowds attended the BBC Good Food Show which featured live cookery demos by TV favourites Paul Hollywood, The Hairy Bikers, John Torode and James Martin, while local star Paul Rankin led Northern Ireland Year of Food & Drink sessions.Two of the North West’s best known chefs, Emmett McCourt (‘Feast or Famine’) and Ian Orr (Browns restaurants) also made special guest appearances on the prestigious Interview Stage. Mayor of Derry and Strabane district, Alderman Hilary McClintock, said she was delighted that LegenDerry Food had been so well promoted at the BBC Good Food Show and was extremely proud of all the work being done by Council and its strategic partners to build on the city’s rising reputation as an international food tourism destination.Pictured above from left are:- Richard Leighton, Doneybrewer Butter; Louise Millsopp, Department of Agriculture, Environment and Rural Affairs (DAERA) NI Regional Food Programme; Mary Blake, Head of Tourism with DCSDC; Alison Leighton, Doneybrewer Butter; Howard Hastings, Managing Director Hastings Hotel Group and former Chair Tourism NI; and Niamh Ashford, Visit Derry.For more information on DCSDC’s events during Northern Ireland Year of Food & Drink 2016 visitwww.derrystrabane.com/foodLEGENDERRY BOOST AT BBC GOOD FOOD SHOW IN BELFAST was last modified: October 17th, 2016 by John2John2 Tags:center_img ShareTweetlast_img read more

August 5, 2019
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There has been strong demand for the flights sinc

first_img“There has been strong demand for the flights since they were announced in December, with the route offering passengers an extremely convenient connection to a host of destinations in the USA and Canada, and we are confident this will continue to grow.”The flight from Belfast to Reykjavik provides easy connections with Icelandair’s wide network of destinations in the US and Canada.Brian Ambrose, Chief Executive of Belfast City Airport, welcomes Arni Gunnarsson, CEO of Air Iceland Connect, to Belfast as the first flight on the new Icelandair route from Belfast to Reykjavik arrived today.One of the most interesting facets of this new route is the ability to stopover in Iceland at no extra cost. So if you are considering flying to the USA or Canada, think again maybe instead of London, try Iceland as its on the way and you could have a stopover of your dreams.Gerry Lennon, Visit Belfast Chief Executive, said:“Air connectivity is critical to us welcoming more international visitors to Belfast and achieving the city’s ambition of doubling tourism spend by 2021.“Icelandair’s new service and extensive global network enables Visit Belfast and our tourism partners to proactively engage with potential visitors, from not only Iceland but other key markets including North America.”Aileen Hickey, Tourism Ireland’s Manager for the Nordic Region, said:“The new Icelandair flight is really good news for tourism to Belfast and Northern Ireland. Not only will it help grow visitor numbers from Iceland, but this new service will also offer connectivity between North America and Belfast. We are delighted to co-operate with Icelandair and Belfast City Airport, to maximise the promotion of this new flight. As an island destination, the importance of convenient flights cannot be overstated – they are absolutely critical to achieving growth in inbound tourism.”Icelandair also began flights to new destination Philadelphia on 30th May 2017, operating four times a week from Reykjavik (KEF) to Philadelphia (PHL) until 20th September 2017. Flights from all seven UK gateways will connect to this. They will also begin flights to Tampa, Florida on 7th September 2017.DD TRAVEL….NICELAND FOR US ALL! was last modified: June 1st, 2017 by John2John2 Tags: The flight time is 2:55 hours to and from George Best Belfast City Airport, which is only five minutes from the city centre.Brian Ambrose, Chief Executive of George Best Belfast City Airport, said:“This is a hugely exciting period for Belfast City Airport following our recent co-hosting of the Routes Europe conference, and the launch of our new three-times weekly flight to Reykjavik will help continue the positive momentum.“We have a strong track record of forming successful partnerships with internationally-renowned airlines such as Icelandair. BIRKIR HOLM GUONASONDD TRAVEL….NICELAND FOR US ALL!GROUP TRAVEL EDITORICELANDAIRTIM HEDGLEY At Belfast City Airport today to launch the new Icelandair route from Belfast City Airport to Reykjavik are Brian Ambrose, Chief Executive of Belfast City Airport, and Arni Gunnarsson, CEO of Air Iceland Connect. Picture by Darren Kidd / Press Eye.BY TIM HEDGLEY, GROUP TRAVEL EDITORICELANDAIR began offering flights from Belfast City Airport (BHD) to Reykjavik (KEF) today, June 1, 2017.The new year-round service will operate up to three times a week on Tuesdays, Thursdays and Sundays.“Icelandair is proud to welcome Belfast on board as our latest UK gateway, working again in partnership with our sister airline Air Iceland Connect who will operate the service.  This addition improves our connectivity and enables us to carry even more passengers to our 18 gateways across the US and Canada, via our hub in Reykjavik.” Said Birkir Holm Guðnason, Icelandair CEO.The new Belfast route is operated by Air Iceland Connect on its 72 seat Bombardier Q400 aircraft in a code sharing partnership with Icelandair, offering great connections at Keflavik International Airport in Iceland to destinations in the US and Canada through Icelandair‘s network. ShareTweetlast_img read more