BEGIN:VCALENDAR
VERSION:2.0
PRODID:https://murmitoyen.com/events/vanille/udem/
X-WR-TIMEZONE:America/Montreal
BEGIN:VEVENT
UID:69def60027d86
DTSTAMP:20260414T222048
DTSTART:20141204T140000
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20141204T140000
URL:https://murmitoyen.com/events/vanille/udem/detail/547451
LOCATION:Université de Montréal - Pavillon Roger-Gaudry\, 2900\, chemin d
 e la Tour\, Montréal\, QC\, Canada\, H3T 1J6
SUMMARY:Soutenance de Doctorat de Solomon Akaraka Owerre
DESCRIPTION:Études de l'effet tunnel des spins quantiques macroscopiquesSt
 udies of the macroscopic quantum tunneling of spinsThe study of molecular 
 magnets has captivated the attention of many researchers in recent years. 
 It has proven be a ubiquitous research area in physics\, with applications
  ranging from quantum information processing\, molecular spintronics to mo
 lecule-based magnetic coolers (magnetocaloric effects). Indeed\, these mol
 ecular magnets are composed of very large spins with large anisotropy\, wh
 ich makes their application to technology more feasible. We present theore
 tical analyses together with experimental observations on macroscopic quan
 tum tunneling and quantum-classical phase transitions of the escape rate i
 n molecular magnets. We consider biaxial ferromagnetic spin systems. Using
  the coordinate dependent spin coherent state path integral\, we obtain th
 e quantum phase interference and the energy splitting of these systems. We
  also present a lucid exposition of tunneling in antiferromagnetic exchang
 e-coupled dimer\, with easy-axis anisotropy. Indeed\, we obtain the ground
  state\, the first excited state\, and the energy splitting\, for both int
 eger and half-odd integer spins. These results are then corroborated using
  perturbation theory and the coordinate independent spin coherent state pa
 th integral. We further present a lucid explication of the effective poten
 tial method\, which enables one to map a spin Hamiltonian onto a particle 
 Hamiltonian\; we employ this method to our models\, however\, in the prese
 nce of an applied magnetic field. This method enables us to investigate qu
 antum-classical phase transitions of the escape rate of these systems. We 
 obtain the phase boundaries\, as well as the crossover temperatures of the
 se phase transitions. Furthermore\, we extend our analysis to one-dimensio
 nal anisotropic Heisenberg antiferromagnet\, with N periodic sites. For e
 ven N\, we show that the ground state is non-degenerate and given by the c
 oherent superposition of the two Neél states. For odd N\, however\, the 
 Neél state contains a soliton\; as the soliton can be placed anywhere alo
 ng the ring\, the ground state is\, indeed\, N-fold degenerate. In the pe
 rturbative limit (weak exchange interaction)\, quantum fluctuation stemmin
 g from the interaction term lifts this degeneracy and reorganizes the stat
 es into a band. We show that this occurs at order 2s in (degenerate) pert
 urbation theory. The ground state is non-degenerate for integer spin\, but
  degenerate for half-odd integer spin\, in accordance with Kramers’ theo
 rem.
END:VEVENT
BEGIN:VTIMEZONE
TZID:America/Montreal
X-LIC-LOCATION:America/Montreal
END:VTIMEZONE
END:VCALENDAR