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• 26 janvier
  [Institut Quantique] Colloque IQ : Michel Gingras
  26 janvier

  [Institut Quantique] Colloque IQ : Michel Gingras

  Lieu : D3-2039 Description : Michel Gingras Université de WaterlooInvité de André-Marie Tremblay  Title:     Frustrated Quantum Rare-Earth Pyrochlores Abstract:The search for magnetic systems that remain disordered down to absolute zero temperature —so-called quantum spin liquids — is a forefront research activity in contemporary condensed matter physics.  Systems of antiferromagnetically interacting magnetic moments (spins) that reside on the sites of lattice architectures made of corner-shared triangles or tetrahedra in two and three-dimensions have been on centre stage of this activity for the past thirty-five years. In this context, materials possessing spin S=1/2 degrees of freedom, expected to have the largest level of quantum fluctuations for having the smallest S value, have attracted foremost interest.  From a materials perspective, the pyrochlore oxides of chemical formula R2M2O7 (where R is trivalent R^{3+} rare-earth ion and M is a tetravalent M^{4+} transition metal ion) would seem particularly attractive  when the interactions are overall antiferromagnetic since the two sets of ions reside on two interpenetrating three-dimensional lattices of corner-shared tetrahedra. Most often, the R^{3+}ions are magnetic — and many theorists and experimentalists have argued that those systems should not host any interesting quantum effects since rare earth ions often possess total angular momenta J=L+S much larger than 1, and should therefore behave essentially  classically. In this talk, I will argue that this perspective is incorrect and discuss few examples of R2M2O7 rare-earth pyrochlore compounds that display interesting quantum effects (e.g. quantum spin ice/spin liquid), even when the system ultimately orders at non-zero temperature (e.g. quantum order-by-disorder).

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• 26 janvier
  [Institut Quantique] Webinaire Curieux quantiques
  26 janvier

  [Institut Quantique] Webinaire Curieux quantiques

  Lieu : https://us06web.zoom.us/j/83953031419?pwd=S28yeWZCUkhwbHJkTTQvSFZJY0swUT09 Description : Vers une carrière en quantique : Opportunités et perspectivesLes sciences quantiques auront des répercussions dans de nombreux champs d'activités. Au delà des percées technologiques, l'industrie naissante du quantique doit relever un défi de taille : Attirer et former le talent. L'Institut quantique de l'Université de Sherbrooke vous présente un webinaire le 26 janvier 2022 à 15h sur l'éducation en quantique, les opportunités qui se dessinent à l'horizon au Québec et ce que la stratégie nationale en quantique du Canada signifie.InscriptionRejoindre l'événementAvec la participation deMichel Pioro-LadrièreDirecteur adjoint, Institut quantiqueDirecteur du baccalauréat en sciences quantiques, UdeSProfesseur dép. de Physique, UdeS Yves Bérubé-LauzièreDirecteur du programme QSciTechProfesseur au dép. de génie électrique et de génie informatique, UdeSOlivier QuirionDirecteur compétences et talent, Innovation, Sciences et Développement économique (ISDE) Canada

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• 27 janvier
  [Institut Quantique] Séminaire virtuel, IQ-RQMP :
  27 janvier

  [Institut Quantique] Séminaire virtuel, IQ-RQMP :

  Lieu : https://umontreal.zoom.us/j/82148683936?pwd=L0ZrcWNFRENadWZLbDJtckFpTG1OUT09 Description :  https://umontreal.zoom.us/j/82148683936?pwd=L0ZrcWNFRENadWZLbDJtckFpTG1OUT09ID de réunion : 821 4868 3936Code secret : 8452Michel Gingras Department of Physics and Astronomy, University of Waterloo, Title: A theoretical outlook on the properties of spin ice and other pyrochlore thin filmsAbstract:Frustrated magnetic materials and strongly correlated electron systems are a forefront of research in modern condensed matter physics and materials science. Despite almost three decades of investigations, the theoretical understanding of these fascinating systems remains incomplete. The most prominent theoretical frameworks used to tackle these systems take the form of an emergent gauge theory akin to the gauge theory that describes conventional electromagnetism. Spin ice is an unusual substance in which the magnetic moments of individual atoms behave very similarly to the protons in conventional water ice — hence the name spin ice — failing to align even at very low temperatures and displaying the same residual entropy that Linus Pauling calculated for water ice and which is measured experimentally. Spin ices, which belong to the broad class of compounds called magnetic pyrochlores, actually have something in common with electromagnetic fields; both can be described by a gauge theory. Many aspects of conventional electromagnetism are sensitive to constraints from enclosure boundaries, such as total internal reflection used in communication with optical fibers. It is then reasonable to wonder if spin ices have similar sensitivities to boundary effects and confinement. Motivated by the recent experimental realizations of spin ice and other magnetic pyrochlore thin films, I will discuss in this talk some of the exotic physical phenomena that arise when considering spin ice thin films such as, for example, a novel magnetic charge crystallization on the film surface while the bulk remains thermally disordered [1]. From a broader context, magnetic pyrochlore thin films offer a natural platform to study the confinement of emergent gauge fields describing strongly correlated systems and the evolution of nontrivial magnetic correlations as one moves from three to two-dimensional spin textures [2]. Finally, I will discuss the consequences of open surfaces on the mechanism of order by disorder in thin films of XY pyrochlore antiferromagnets. We find that a complex competition between multiple orders take place, as a function of temperature and film thickness. A gradient of ordering spreads over long length scale inside the film while the nature of the phase transitions is blurred between two and three dimensional critical phenomena [3]. Beyond the physics of films, this work may also pertain to near-surface effects in single crystals of rare-earth pyrochlore oxides. [1] L. D. C. Jaubert, T. Lin, T. S. Opel, P. C. W. Holdsworth and M. J. P. Gingras; Phys. Rev. Lett. 118, 207206 (2017).[2] Étienne Lantagne-Hurtubise, Jeffrey G. Rau and Michel J. P. Gingras; Phys. Rev. X 8, 021053 (2018).[3] L.D.C. Jaubert, J.G. Rau, P. C. W. Holdsworth and M. J. P. Gingras; in preparation.   

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