Nouvelles

Événements

• 30 novembre
  [Institut Quantique] MatQ:
  30 novembre

  [Institut Quantique] MatQ:

  Lieu : https://umontreal.zoom.us/j/93026432919?pwd=SkVyQ2w2Z3Q2SW5CcjJQa2QwVlRsZz09 Description : https://umontreal.zoom.us/j/93026432919?pwd=SkVyQ2w2Z3Q2SW5CcjJQa2QwVlRsZz09 Meeting ID: 930 2643 2919Password: 137*************************************************************************** Étienne LefrançoisDépartement de physique, Université de Sherbrooke Véronique Brousseau-CoutureDépartement de physique, Université de Montréal TITRE / TITLE: Thermal transport study in the Kitaev spin liquid candidate RuCl3TITRE / TITLE: Predominance of non-adiabatic effects in the zero-point renormalization of the band gap: connecting first-principles approach and the Fröhlich modelQUAND / WHEN: Lundi 30 novembre, à 10h30 OÙ / WHERE: Zoom Meetinghttps://umontreal.zoom.us/j/93026432919?pwd=SkVyQ2w2Z3Q2SW5CcjJQa2QwVlRsZz09 Meeting ID: 930 2643 2919Password: 137 RÉSUMÉ / ABSTRACT:Thematerial a-RuCl3 has been extensively researched as a potential candidate forKitaev quantum spin liquid, whose low-energy excitations are expected to beMajorana fermions. Note that a-RuCl3 orders antiferromagnetically atlow temperature, under TN = 7 K, but an external magnetic field inthe plane, greater than H|| = 7 T, removes this order. The question is whetheror not there is, over a range of fields greater than 7 T, an orderless regionthat harbours a liquid state of quantum spin. The recent announcement of aquantized thermal Hall conductivity at H|| > 7 T by Kasahara et al.[Kasahara et al., Nature 559, 227 (2018)] would be the first direct evidence ofitinerant Majorana fermions in a quantum spin liquid state. In the study wepresent here, we examine the origin of thermal Hall conductivity kxyin a-RuCl3. The comparison between the longitudinal thermal conductivitykxx and kxy suggests that the thermal Hall conductivitysignal is mainly dominated by phonons - questioning the possibility of aquantified kxy. In addition, depending on the H|| field, we do notsee an intermediate region between the antiferromagnetic state under 7 T andthe state of polarized spins at strong field, thus leaving little room for aquantum spin liquid state. RÉSUMÉ / ABSTRACT: Electronicand optical properties of materials are affected by atomic motion through theelectron-phonon interaction. As a consequence, band gaps acquire a temperaturedependence, and are affected even at absolute zero temperature, where thezero-point motion of the ions causes zero-point renormalization (ZPR) of theband gap. From a first-principles point of view, different methodologies havebeen used throughout the literature to compute the ZPR, relying on differentapproximation schemes. One of the most widely used is the adiabaticapproximation, which supposes that the electrons adjust instantaneously to theperiodic modulation of the crystal potential created by phonons. I will presentnumerical results for the ZPR of 30 materials, and show that global agreementwith available experimental data is obtained only when non-adiabatic effectsare taken into account. I will then demonstrate that these effects dominate theZPR for many materials, by introducing a generalized Fröhlich model thataccounts for multiple phonon branches, as well as anisotropic and degenerateband extrema. I will finally address the physical mechanism that is brought tolight by these results.***************************************************************************

  En voir +
• 01 décembre
  [Institut Quantique] InfoQ – Groupes Kourtis/Reulet
  01 décembre

  [Institut Quantique] InfoQ – Groupes Kourtis/Reulet

  Lieu : Description : Rejoindre la réunion Microsoft Teams  

  En voir +
• 01 décembre
  [Institut Quantique] Horizon IQ – Bryan Dewsbury – Pédagogie inclusive / Inclusive teaching
  01 décembre

  [Institut Quantique] Horizon IQ – Bryan Dewsbury – Pédagogie inclusive / Inclusive teaching

  Lieu : Description : Rejoindre la réunion Zoom / Join the Zoom meetingLe séminaire sera donné en anglais. The seminar will be given in English.Bryan DewsburyInvité de DiPhUsTitre/TitlePédagogie inclusive / Inclusive teachingRésumé/Abstract

  En voir +