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UID:DSC-9962
DTSTART;TZID=Europe/Berlin:20150928T163000
SEQUENCE:1443426603
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20150928T173000
URL:https://dresden-science-calendar.de/calendar/de/detail/9962
LOCATION:MPI-PKS\, Nöthnitzer Straße 3801187 Dresden
SUMMARY:Takagi: Exotic electronic states produced by strong spin-orbit coup
 ling in complex Ir oxides
CLASS:PUBLIC
DESCRIPTION:Speaker: Hidenori Takagi\nInstitute of Speaker: MPI für Festk
 örperforschung Stuttgart\nTopics:\nPhysik\n Location:\n  Name: MPI-PKS (S
 eminarroom 1+2+3)\n  Street: Nöthnitzer Straße 38\n  City: 01187 Dresden
 \n  Phone: + 49 (0)351 871 0\n  Fax: \nDescription: In 5d Iridium oxides\,
  a large spin-orbit coupling of ~0.5 eV\, inherent to heavy 5d elements\, 
 is not small as compared with other relevant electronic parameters\, inclu
 ding Coulomb U\, transfer t and crystal field splitting D\, which gives ri
 se to a variety of exotic magnetic ground states. In the layered perovskit
 e $Sr_{2}IrO_{4}$\, spin-orbital Mott state with Jeff=1/2 is realized due 
 to the novel interplay of those energy scales [1-3]. Despite the strong en
 tanglement of spin and orbital degrees of freedom\, $J_{eff}$=1/2 iso-spin
 s in $Sr_{2}IrO_{4}$ was found to be surprisingly isotropic\, very likely 
 due to a super-exchange coupling through almost 180° Ir-O-Ir bonds [4]. T
 he temperature dependence of in-plane magnetic correlation length of $J_{e
 ff}$=1/2 iso-spins\, obtained from inelastic x-ray resonant magnetic scatt
 ering\, was indeed well described by that expected for two-dimensional S=1
 /2 Heisenberg antiferromagnet [5]. The three-dimensional analog of $Sr_{2}
 IrO_{4}$\, $SrIrO_{3}$ perovskite is very close a band insulator due to la
 ttice distortion but a Dirac semimetal protected by crystalline symmetry [
 6]. Upon increasing effective Coulomb U\, magnetism emerges and creates a 
 gap at Dirac nodes\, giving rise to a semimetal to magnetic insulator tran
 sition. This can be realized by controlling the dimensionality and hence t
 he effective U in $(SrIrO_{3})_{m}/SrTiO_{3}$ (m: number of $SrIrO_{3}$ la
 yer) super-lattice structure [7]. With reducing m\, a transition to an ins
 ulator\, accompanied with magnetism was clearly observed. At m=1\, single 
 layer\, the transport remains insulating even above the magnetic ordering 
 temperature\, indicative of the increased Mott character. When Jeff=1/2 is
 o-spins interact with each other through 90° Ir-O-Ir bonds\, very anisotr
 opic bond dependent ferromagnetic coupling is expected\, unique to strong 
 SOC system. Complex Ir oxides with honeycomb and more recently identified 
 hyper-honeycomb lattices [8]\, where x-\, y- and z- 90° Ir-O-Ir bonds are
  realized\, may be candidates for quantum spin liquid expected for the Kia
 tev model. Very likely due to the superposition of additional magnetic cou
 plings not included in the Kitaev model [9]\, in reality\, a long range ma
 gnetic ordering emerges at low temperatures in those compounds. Hyper-hone
 ycomb $\\beta-Li_{2}IrO_{3}$\, though eventually show a marginal ordering\
 , appears to be located at the critical vicinity to the Kitaev spin liquid
 . 1) B. J. Kim et al.\, Phys. Rev. Lett. 101\, 076402 (2008). 2) B. J. Kim
  et al.\, Science 323\, 1329 (2009). 3) S. Fujiyama et al.\, Phys. Rev. Le
 tt. 112\, 016405 (2014). 4) G. Jackeli and G. Khaliullin\, Phys. Rev. Lett
 . 102\, 017205 (2009). 5) S. Fujiyama et al.\, Phys. Rev. Lett. 108\, 2472
 12 (2012). 6) Chen\, Y. et al. \,Nat. Commun. 6:6593 doi: 10.1038/ncomms75
 93 (2015). 7) J. Matsuno et al.\, Phys. Rev. Lett. (2015). 8) T.Takayama\,
  et al.\, s Phys. Rev. Lett.114\, 077202 (2015). 9) A.Kitaev\, Annals of P
 hysics 312 2 (2006).
DTSTAMP:20260425T145755Z
CREATED:20150924T075157Z
LAST-MODIFIED:20150928T075003Z
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