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ARPES study of metal-insulator transition in Sr 2 IrO 4

ARPES study of metal-insulator transition in Sr 2 IrO 4. Véronique Brouet, Alex Louat , Lise Serrier -Garcia, Fabrice Bert Laboratoire de Physique des Solides d’Orsay. ARPES experiments : SOLEIL synchrotron, CASSIOPEE beamline

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ARPES study of metal-insulator transition in Sr 2 IrO 4

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  1. ARPES study of metal-insulator transition in Sr2IrO4 Véronique Brouet, Alex Louat, Lise Serrier-Garcia, Fabrice Bert Laboratoire de Physique des Solides d’Orsay ARPES experiments : SOLEIL synchrotron, CASSIOPEE beamline Patrick Le Fèvre, François Bertran, Julien Rault Samplesynthesis LPS in collaboration with I.R. Fisher, S.C Riggs, M.C. Shapiro, Paula Giraldo-Giro : Stanford University and Dorothée Colson, Anne Forget : SPEC, CEA-Saclay, France

  2. Outline • New type of Mottinsulator : • => Spin-orbitMottinsulator • => Are theysimilar to cuprates ? • New type of correlatedmetals ? • ARPES study of the evolution of the electronic structure through the metal-insulator transition • Doping through Sr/La substitutions • => Doping through Ir/Rh substitutions • Rh doping induces charge defects, whichgive the opportunity to study the role of defects in iridates Sr2IrO4 (simplified structure)

  3. Sr2IrO4 : a spin-orbitMottinsulator Weakcorrelations are expected for 5d metals. However, the strong spin-orbitsplittingreshapes the band structure in a waythatfavorsstrongcorrelations. B.J. Kim et al. PRL 2008 Jeff=1/2 Jeff=3/2 Strongcorrelations Mottinsulator Ratherweakcorrelations Sr2IrO4 (simplified structure) Supported by DMFT calculationsC. Martins, S. Biermannet al. PRL 11

  4. Sr2IrO4 : an insulatorwith AF transition at 240K Resistivity => insulatingbelow and above TN Magneticorderbelow TN=240K M=0,2mB/Ir Feng Ye, PRB13 Dhital PRB 13 Chikara, G. Cao et al. PRB09 Mott gap ~ 0,6eV Magnetic exchange J~60meV Analogywith cuprates => superconducting if doped ?? Wang, Senthil PRL 2011

  5. Towards a metallic state Resistivity Magnetization (1T) Metalliclikeslopes ou obtainedwithsmallupturnsatlow T. The magnetic transition isquicklysuppressed by substitutions. Seealso : M. Ge, G. Cao, PRB 2011 X. Chen, D. Wilson, PRB 15… • => No superconductivityobservedso far

  6. Is itsimilar to cuprates ? Fermi Surface observedwith ARPES K evaporator Y.K. Kim et al., Science 14 • The evolution of the Fermi Surface seems to exhibit « Fermi arcs » like cuprates • A d-wave gap could open at 50K Y.K. Kim Nature Phys. 2015, Y.J. Yan PRX 15

  7. Electron analyser Z hv e- q Y f X Crystal Angle-resolvedphotoemission Sr2IrO4 : Energy-momentum plots

  8. Whatwillhappenwhen doping ? Fermi Surface Band structure Metallic state expectedfrom DFT Gap

  9. La doping Fermi Surface for 4% La doped mLa Sr/La La/Sr substitutions = electron doping J=3/2 V. Brouet et al., PRB 15 Seealso : A. De La Torre, F. Baumberger PRL 15 Whyisitdifficult to dope with La ? How does Rh doping proceed ?

  10. Whyis La doping limited to ~5% ? Fermi Surface for 4% La doped Surface doped Samebehaviorwithlimited doping range ? Role of dopant ? Y.K. Kim et al., Science 14

  11. Rh doping Sr2RhO4metallic Sr2IrO4insulating Isovalent substitution (Ir4+=Rh4+=d5) => Reduced spin-orbit ? DestabilizeMott gap ? Ir/Rh => Rh induces effective hole doping • X-ray absorption typical of Rh3+ • Clancy et al. PRB 14 • ARPES observedholepockets • Y. Cao, D. Dessau et al., Nat Com 16

  12. One electronistrapped at Rh site hole Ir Smallerhybridization withoxygenfavorsRh3+=d6 ? Smaller value of l favors Rh3+=d6 ? Ir Ir Rh +1e- Ir Rh O Ir Ir Ir Ir Ir Y. Cao, D. Dessau et al., Nature Com. 16 Ir Ir • Local chargeddefects are formed and are stable • Theymaybestabilized by a differenthybridizationwithoxygen • This type of trappingmayalsoplay a role for otherways of doping

  13. Hole pockets at 15% Rh doping Dispersion alongGX Fermi Surface mRh Not a simple metal : no QP peak Dispersion alongGM Louat, V. Brouet PRB 18 Seealso : Yao, Dessau et al., Nat Com 16

  14. Pseudogapwith Rh doping Dispersion alongGX Fermi Surface 60meV pseudogap Position of leadingedge vs theta A. Louat, V. Brouet et al., PRB 18

  15. A correlated and disorderedmetal Mean free path (from ARPES MDC) Nb of holesfrom FS pocket area ARPES XAS Chikara PRB17

  16. A correlated and disorderedmetal Distance betweenholes vs mean free path (from ARPES MDC) Nb of holesfrom FS pocket area ARPES XAS Chikara PRB17 « metal » Transport MottinsulatorAnderson insulator The incoherentmetalischaracterized by absence of QP or 50meV pseudogap Seealso : T.F. Qi, G. Cao et al., PRB 12

  17. Conclusions Iridates are difficult to dope, whichlimits the possibilities of comparisonwith cuprates Rh doping triggers the formation of local chargeddefects => Opportunity to study how thesesystemsreact to defects (role of oxygen…) => Opportunity to study a disorderedcorrelatedmetal Is ittypicalfrom 5d systems ? Thanks to financial support from French National Agency for research ANR « SOCRATE » 2015-2020

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