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• 05 December
  [Institut Quantique] Projet Porteur – Excitations émergentes dans les matériaux quantiques / Harnessing emergent excitations in quantum materials
  05 December

  [Institut Quantique] Projet Porteur – Excitations émergentes dans les matériaux quantiques / Harnessing emergent excitations in quantum materials

  Location : Description : Lieu/Location : Auditorium de l'IQDes biscuits seront offerts dans la cuisinette de l’IQ dès 10h30, heure à partir de laquelle le café sera gratuit jusqu’à 11h00. Le séminaire débutera à 11h00. Venez en grand nombre!Cookies will be available in the IQ kitchenette starting at 10:30, at which time coffee will be free until 11:00. Talk starts at 11:00. A nice occasion to discuss! Premier conférencier : Q. BarthélemyInstitut Quantique, Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, CanadaHeat conduction in herbertsmithite:field dependence at the onset of the quantum spin liquid regimeRésumé: Herbertsmithite ZnCu3(OH)6Cl2 is an emblematic quantum spin liquid candidate because it is the closest realization of the nearest-neighbor S = 1/2 kagome Heisenberg antiferromagnet with a dynamical ground state. After recalling some selected developments of our 17O NMR and high-field specific studies [1, 2], I will present our recent thermal transport study [3], where we report thermal conductivity measurements on high quality single crystals over a wide range of temperatures (0.05-120 K) in magnetic fields up to 15 T. We also report measurements of the thermal Hall effect, found to be vanishingly small. At high temperatures, in the paramagnetic regime, the thermal conductivity has a negligible field dependence. Upon cooling and the development of correlations, the onset of a clear monotonic field dependence below about 20 K signals a new characteristic temperature scale that may reflect the subtle crossover towards the quantum spin liquid regime. Deconfined spinons, if present, are not detected and phonons, as the main carriers of heat, are strongly scattered by the intrinsic spin excitations and the magnetic defects. In view of the colossal fields required to affect the intrinsic spins, most of the field-induced evolution is attributed to the progressive polarization of some magnetic defects. By elaborating a phenomenological model, we extract the magnetization of these main scattering centers which does not resemble the Brillouin function for free spins 1/2, requiring to go beyond the paradigm of isolated paramagnetic spins. Besides, the onset of a nonmonotonic field dependence below about 2 K underlines the existence of another characteristic temperature scale, previously highlighted with other measurements, and sheds new light on the phase diagram of herbertsmithite down to the lowest temperatures.[1] P. Khuntia et al., Nature Physics 16, 469 (2020)[2] Q. Barthélemy et al., Physical Review X 12, 011014 (2022)[3] Q. Barthélemy et al., arXiv:2211.08546 (2022) Deuxième conférencier: N. GauthierThe quest for quantum spin liquids in Ce-based pyrochlores Rare-earth based pyrochlore magnets form alarge family of geometrically frustrated magnets that exhibit analogous effects to the proton disorder in water ice. The disordered magnetic ground state in pyrochlore materials was named spin ice due to this similarity with water ice. Classical spin ice states have been extensively studied in Dy2Ti2O7and Ho2Ti2O7. Such states are driven by thermal fluctuations and exhibit slow dynamics at low temperatures. In contrast, quantum fluctuations can generate long-range entanglement of the magnetic moments, a state of matter called quantum spin liquid, and more specifically, a quantum spin ice for pyrochlore materials. The fundamentally quantum nature of this state attracts great interest, in particular because it is a playground to study emergent gauge theories with fractionalized excitations. The quantum spin ice state is predicted to host visons and photons, emergent excitations without any classical analogue. Demonstrating the existence of these excitations would be a milestone to establish experimentally the existence of quantum spin liquids.Ce-based pyrochlore magnets are promising candidates to host a quantum spin ice state and I will discuss our past, present and future works on these materials. Using a combination of experimental techniques, we previously evidenced that Ce2Sn2O7exhibits many key features expected from a quantum spin ice state. More recently, we investigated the low energy excitations of Ce2Hf2O7using specific heat measurements. Our results showcase the relevant energy scales of the emergent excitations. In this context, I will describe the predicted experimental signatures associated with the emergent photon. I will specifically discuss the feasibility of a recent proposal to measure the photon velocity using ultrasound velocity measurements [Simon, et al., PRB 106, 064427(2022)]. 

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• 06 December
  [Institut Quantique] Projet Porteur – Matière ultra quantique : les supraconducteurs à base de cuprate / Cuprate superconductors as ultra quantum matter : New tools and discoveries
  06 December

  [Institut Quantique] Projet Porteur – Matière ultra quantique : les supraconducteurs à base de cuprate / Cuprate superconductors as ultra quantum matter : New tools and discoveries

  Location : Description : Lieu/Location : Auditorium de l'IQDes biscuits seront offerts dans la cuisinette de l’IQ dès 10h30, heure à partir de laquelle le café sera gratuit jusqu’à 11h00. Le séminaire débutera à 11h00. Venez en grand nombre!Cookies will be available in the IQ kitchenette starting at 10:30, at which time coffee will be free until 11:00. Talk starts at 11:00. A nice occasion to discuss!Séminaire/Seminar #1Lu ChenPostdoc - Groupe de Louis TailleferTitre/TitleElectrons with Planckian Scattering Obey Standard Orbital Motion in a Magnetic Feild     Résumé/AbstractIn various so-called strange metals, electrons undergo Planckian dissipation, a strong and anomalous scattering that grows linearly with temperature, in contrast to the quadratic temperature dependence expected from the standard theory of metals. In some cuprates and pnictides, a linear dependence of resistivity on a magnetic field has also been considered anomalous—possibly an additional facet of Planckian dissipation. Here we show that the resistivity of the cuprate strange metals Nd0.4La1.6−xSrxCuO4 and La2−xSrxCuO4 is quantitatively consistent with the standard Boltzmann theory of electron motion in a magnetic field, in all aspects—field strength, field direction, temperature and disorder level. The linear field dependence is found to be simply the consequence of scattering rate anisotropy. We conclude that Planckian dissipation is anomalous in its temperature dependence, but not in its field dependence. The scattering rate in these cuprates does not depend on field, which means that their Planckian dissipation is robust against fields up to at least 85 T.Séminaire/Seminar #2Maxime Massoudzadegan  Étudiant au doctorat - Groupe de Bertrand ReuletTitre/TitleRésumé/Abstract

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• 06 December
  [Institut Quantique] Visite retraités Faculté des sciences
  06 December

  [Institut Quantique] Visite retraités Faculté des sciences

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