BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Non-conservation of the valley density and its implications for th
 e observation of the valley Hall effect - Alessandro Principi\, University
  of Manchester
DTSTART:20240229T140000Z
DTEND:20240229T150000Z
UID:TALK205072@talks.cam.ac.uk
CONTACT:Gaurav
DESCRIPTION:We show that the conservation of the valley density in multi-v
 alley insulators is broken in an unexpected way by the electric field that
  drives the valley Hall effect.  This implies that  time-reversal-invarian
 t fully-gapped  insulators\, in which no bulk or edge state crosses the Fe
 rmi level\, can support a valley Hall current in the bulk and yet show no 
 valley density accumulation  at the edges.  Thus\, the valley Hall effect 
 cannot be observed in such systems. If the system is not fully gapped then
  valley density accumulation at the edges is possible. The accumulation ha
 s no contribution from undergap states and can be expressed as a Fermi sur
 face average\, for which we derive an explicit formula.  \nWe demonstrate 
 the theory by calculating the valley density accumulations  in an archetyp
 ical valley-Hall insulator: a gapped graphene nanoribbon. Surprisingly\, w
 e discover that a net valley density polarization is dynamically generated
  for certain edge terminations.\n
LOCATION:TCM Seminar Room
END:VEVENT
END:VCALENDAR