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ARPES Study of Metal-Insulator Transition in Sr2IrO4

Investigating the metal-insulator transition in Sr2IrO4 using ARPES experiments at the SOLEIL synchrotron's CASSIOPEE beamline. Explore the unique properties of this spin-orbit Mott insulator and its similarities to cuprates. Doping studies through Sr/La and Ir/Rh substitutions provide insights into the role of defects and correlated metals. Discover the challenges in doping with La and the effects of Rh doping on the electronic structure. Uncover the formation of local charged defects with Rh doping and their impact on the system's behavior. This research sheds light on the evolution of Fermi surface and band structure, and the transition to a correlated and disordered metal state in Sr2IrO4.

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ARPES Study of Metal-Insulator Transition in Sr2IrO4

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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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