ARPES study of metalinsulator transition in Sr 2

ARPES study of metal-insulator transition in Sr 2 Ir. O 4 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 Sample synthesis 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

Outline • New type of Mott insulator : => Spin-orbit Mott insulator => Are they similar to cuprates ? • New type of correlated metals ? ARPES study of the evolution of the electronic structure through the metal-insulator transition Þ Doping through Sr/La substitutions => Doping through Ir/Rh substitutions Sr 2 Ir. O 4 (simplified structure) • Rh doping induces charge defects, which give the opportunity to study the role of defects in iridates

Sr 2 Ir. O 4 : a spin-orbit Mott insulator Weak correlations are expected for 5 d metals. However, the strong spin-orbit splitting reshapes the band structure in a way that favors strong correlations. B. J. Kim et al. PRL 2008 Jeff=1/2 Jeff=3/2 Sr 2 Ir. O 4 (simplified structure) Rather weak correlations Strong correlations Supported by DMFT calculations C. Martins, S. Biermann et al. PRL 11 Mott insulator

Sr 2 Ir. O 4 : an insulator with AF transition at 240 K Resistivity => insulating below and above TN Magnetic order below TN=240 K M=0, 2 m. B/Ir Feng Ye, PRB 13 Dhital PRB 13 Chikara, G. Cao et al. PRB 09 Mott gap ~ 0, 6 e. V Magnetic exchange J~60 me. V Analogy with cuprates => superconducting if doped ? ? Wang, Senthil PRL 2011

Towards a metallic state Resistivity Metallic like slopes ou obtained with small upturns at low T. Magnetization (1 T) The magnetic transition is quickly suppressed by substitutions. => No superconductivity observed so far See also : M. Ge, G. Cao, PRB 2011 X. Chen, D. Wilson, PRB 15…

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

Angle-resolved photoemission Z hv q Electron analyser e. Y f X Crystal Sr 2 Ir. O 4 : Energy-momentum plots

What will happen when doping ? Fermi Surface Band structure Gap Metallic state expected from DFT

La doping m. La Fermi Surface for 4% La doped La/Sr substitutions = electron doping Sr/La J=3/2 V. Brouet et al. , PRB 15 See also : A. De La Torre, F. Baumberger PRL 15

Why is La doping limited to ~5% ? Fermi Surface for 4% La doped Surface doped Same behavior with limited doping range ? Role of dopant ? Y. K. Kim et al. , Science 14

Rh doping Sr 2 Rh. O 4 metallic Sr 2 Ir. O 4 insulating Isovalent substitution (Ir 4+=Rh 4+=d 5) => Reduced spin-orbit ? Destabilize Mott gap ? Ir/Rh => Rh induces effective hole doping - X-ray absorption typical of Rh 3+ Clancy et al. PRB 14 - ARPES observed hole pockets Y. Cao, D. Dessau et al. , Nat Com 16

One electron is trapped at Rh site Ir hole Rh Ir +1 e- Ir Smaller hybridization with oxygen favors Rh 3+=d 6 ? Ir Ir Ir Smaller value of l favors Rh 3+=d 6 ? O Ir Ir Y. Cao, D. Dessau et al. , Nature Com. 16 Þ Local charged defects are formed and are stable Þ They may be stabilized by a different hybridization with oxygen Þ This type of trapping may also play a role for other ways of doping Rh

Hole pockets at 15% Rh doping Fermi Surface Not a simple metal : no QP peak m. Rh Dispersion along GX Dispersion along GM

Pseudogap with Rh doping Dispersion along GX Fermi Surface Position of leading edge vs theta 60 me. V pseudogap A. Louat, V. Brouet et al. , PRB 18

A correlated and disordered metal Nb of holes from FS pocket area Mean free path (from ARPES MDC) ARPES XAS Chikara PRB 17

A correlated and disordered metal Nb of holes from FS pocket area Distance between holes vs mean free path (from ARPES MDC) ARPES XAS Chikara PRB 17 « metal » Transport Mott insulator Anderson insulator The incoherent metal is characterized by absence of QP or 50 me. V pseudogap See also : T. F. Qi, G. Cao et al. , PRB 12

Conclusions Iridates are difficult to dope, which limits the possibilities of comparison with cuprates Rh doping triggers the formation of local charged defects => Opportunity to study how these systems react to defects (role of oxygen…) => Opportunity to study a disordered correlated metal Is it typical from 5 d systems ? Thanks to financial support from French National Agency for research ANR « SOCRATE » 2015 -2020