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SUMMARY:Emergent chirality in charge ordered materials - Jasper van Wezel\
 , Argonne
DTSTART:20120613T101500Z
DTEND:20120613T111500Z
UID:TALK38337@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:The formation of long range order in a material undergoing a p
 hase transition is accompanied by the breakdown of a corresponding symmetr
 y. Magnetic order for example\, breaks spin rotational symmetry\, while su
 perconductivity breaks a global phase symmetry\, and density waves break t
 ranslational symmetry. Apart from these direct effects on the symmetry of 
 the material\, concomitant changes in the interactions of the lattice\, or
 bital\, spin and charge degrees of freedom may lead to the 'accidental' br
 eakdown of additional symmetries. These additional broken symmetries are k
 ey in our understanding of many material properties.\n \nIn this seminar\,
  I will describe how the onset of a specific charge ordered state may be a
 ccompanied by the breakdown of inversion symmetry\, giving rise to a polar
  or even a chiral phase. Unlike the case of magnetic materials\, in which 
 this type of broken inversion symmetry is common\, owing to the ease of fo
 rming helical arrangements of spin vectors\, the scalar charge density is 
 not so readily coerced into a chiral arrangement. I will indicate how the 
 interplay between charge and orbital degrees of freedom is essential in th
 e formation of this novel state of matter.\n\nThe chiral or polar charge a
 nd orbital order can be observed using a variety of experimental probes. I
  will discuss recent X-ray and transport measurements performed at Argonne
 's Materials Science Division\, which provide the first experimental evide
 nce for the presence of a hierarchy of transitions involved in the onset o
 f chiral charge order in TiSe2\, in close agreement with theoretical predi
 ctions.\n\nReferences:\n1. J. Ishioka et al.\, Phys. Rev. Lett.\, 105\, 17
 6401 (2010).\n2. J. van Wezel\, Europhys. Lett.\, 96\, 67011 (2011).\n3. J
 . van Wezel\, Phys. Rev. B\, 85\, 35131 (2012).\n4. J.-P. Castellan et al.
 \, arxiv/1204.1374
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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