BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//talks.cam.ac.uk//v3//EN
BEGIN:VTIMEZONE
TZID:Europe/London
BEGIN:DAYLIGHT
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
TZNAME:BST
DTSTART:19700329T010000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
TZNAME:GMT
DTSTART:19701025T020000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CATEGORIES:Theory of Condensed Matter
SUMMARY:Order by disorder and phase transitions - Laura M
essio\, LPTMC Paris
DTSTART;TZID=Europe/London:20220120T140000
DTEND;TZID=Europe/London:20220120T150000
UID:TALK161536AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/161536
DESCRIPTION:In most phase transitions\, the low temperature ph
ase possesses a broken symmetry\, that is restored
above a critical temperature (with the notable ex
ception of topological phase transitions). This br
oken symmetry is associated to a non-zero order pa
rameter\, and the ground state(s) (at T=0) usually
maximizes(s) this order parameter. This is not th
e case in the presence of order by disorder\, wher
e entropic effects are responsible for the enhance
ment of the order parameter. This situation occurs
in the Vesignieite compound BaCu3V2O8(OH)2\, a Mo
tt insulator modeled by a J1-J3 Heisenberg model o
n the kagome lattice (with first and third neighbo
r interactions). The nature of the classical groun
d state and the possible phase transitions are inv
estigated through analytical and numerical calcula
tions. This model has many similarities with the J
1-J2 square lattice\, known to develop a collinear
phase for J2>J1|/2 through the order by disorder
mechanism. In both model\, the limit of large J2 o
r J3 gives several decoupled sublattices and J1 do
es not lift the ground state degeneracy. On both l
attices\, collinear spin configurations are favore
d by fluctuations\, giving rise to a discrete orde
r parameter and to a finite temperature phase tran
sition. On the kagome lattice\, a q=4 Potts parame
ter emerges\, against a Z2 on the square lattice.
Effect of quantum fluctuations are studied through
linear spin wave approximation and high temperatu
re expansions of the S=1/2 model.\n\nReference: V.
Grison et al\, Phys.Rev.B 102\, 214424 (2020)
LOCATION:Details of video conferencing will be distributed
nearer the time.
CONTACT:Jan Behrends
END:VEVENT
END:VCALENDAR