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SUMMARY:Magnetic Moment Fragmentation in Spin Ice and Artificial Spin Ice 
 - Prof. Peter Holdsworth\, ENS Lyon
DTSTART:20170518T130000Z
DTEND:20170518T140000Z
UID:TALK72311@talks.cam.ac.uk
CONTACT:Gareth Conduit
DESCRIPTION:Magnetic systems where interactions and lattice geometry fail 
 to produce conventional (e.g.\, ferromagnetic or antiferromagnetic) ordere
 d states are referred to as being frustrated. This phenomenon often leads 
 to an effectively reduced Hilbert space at low energy/temperature that has
  enhanced -- or emergent -- symmetries. A case in point is the so-called C
 oulomb phase [1\,2] in dimer and ice models\, where the magnetic configura
 tions acquire an emergent gauge symmetry and dipolar correlations. In this
  talk I will introduce these concepts at a pedagogical level and illustrat
 e their experimental signatures (for instance in the form of so-called pin
 ch-point scattering patterns in the structure factor) in solid-state frust
 rated magnets and artificial arrays of magnetic nano-particles.\nI will th
 en focus on model spin ice and artificial systems where the the emergent f
 ield can be separated into divergence full and divergence free parts\, fol
 lowing a Helmholz decomposition [3]. As a consequence the configuration of
  magnetic moments naturally fragments into two distinct fields\, one provi
 ding a dense pattern of `magnetic charges'\, and the other providing a per
 sistent fluctuating background. Driving the system into an ordered charge 
 crystal phase leads only to partial ordering of the spins\, with one compo
 nents providing the Bragg peaks of the ordered state and the other a magne
 tic fluid with all the characteristics of an emergent Coulomb phase. Speci
 fic examples include a monopole crystal phase for spin ice and the charge 
 ordered KII phase of artificial kagome ice [3]. Recent experiments have sh
 own evidence of this fragmentation in three dimensions\, in the frustrated
  pyrochlore magnet Nd2Zr2O7 [4]\, in artificial kagome ice [5] and in the 
 layered quasi-two-dimensional magnet Dy3Mg2Sb3O14 [6]\, and I shall commen
 t on these exciting developments. \n\n[1] C. L. Henley\, Annu. Rev. Conden
 s. Matter Phys. 1\, 179(2010)\;\n\n[2]S. V. Isakov\, K. Gregor\, R. Moessn
 er\, and S. L. Sondhi\, Phys. Rev. Lett.\, 93\, 167204 (2004)\;\n\n[3] M. 
 Brooks-Bartlett\, S. Banks\, L. Jaubert\, A. Harman-Clarke\, P. C. W. Hold
 sworth\, Phys. Rev. X4\, 011007 (2014)\;\n\n[4] S. Petit et. al. \, Nature
  Physics (2016)\, doi:10.1038/nphys3710\;\n\n[5] Benjamin Canals et. al. \
 , Nature Communications (2016) 7\, 11446\;\n\n[6] Joseph A. M. Paddison et
  al. Nature Communications (2016) 7\, 13842.\n
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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