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URL:https://murmitoyen.com/events/vanille/udem/detail/785086-weyl-semimetal
 s-in-extreme-magnetic-fields-brad-ramshaw-cornell
LOCATION:Université de Montréal - Pavillon J.-Armand-Bombardier\, 5155\, 
 chemin de la rampe \, Montréal\, QC\, Canada\, H3T 2B2
SUMMARY:Weyl semimetals in extreme magnetic fields - Brad Ramshaw (Cornell)
DESCRIPTION:Weyl semimetals in extreme magnetic fieldsBrad RamshawPhysics D
 epartmentCornell University
\nAbstract: Under extreme magnetic fields elec
 trons in a metal are confined to a single highly-degenerate Landau level -
  a regime known as the quantum limit. Electrons under such conditions are 
 unstable to the formation of new states of matter\, such as the fractional
  quantum Hall states in two dimensions. The fate of 3D metals in the quant
 um limit\, on the other hand\, has been relatively unexplored. The discove
 ry of monopnictide Weyl semimetals brings a new ingredient to the table - 
 chiral 'Weyl' fermions. These quasiparticles are similar to Dirac quasipar
 ticles in graphene\, but their 'spin up' and 'spin down' states are separa
 ted due to broken inversion symmetry and spin-orbit coupling. We use magne
 tic fields up to 95 Tesla to take the Weyl semimetal TaAs into its ultra-q
 uantum limit\, isolating its 0th Landau level from the rest of the electro
 nic spectrum\, and observe two transitions as a function of field. The fir
 st is accompanied by a two-order-of-magnitude increase in the resistivity\
 , indicating a gapped state. The second transition is accompanied by a lar
 ge increase in ultrasonic attenuation\, suggesting the onset of a mesoscop
 ically disordered state\, perhaps reminiscent of the 'bubble and stripe' p
 hases seen in two dimensional electron gasses. At present we are combing m
 icrostructured transport\, infrared spectrometry\, and ultrasound to ident
 ify this potentially new state of matter that arises from Weyl fermions.
\
 nTo know more about Prof. Ramshaw\, you can consult his web page.
\nCette 
 conférence est présentée par le RQMP Versant Nord du Département de
  physique de l'Université de Montréal et de Génie physique de la Pol
 ytechnique.
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