IRG-1 CEM CENTER FOR EMERGENT MATERIALS SPIN-ORBIT COUPLING IN CORRELATED MATERIALS: SEARCH FOR NOVEL PHASES AND PHENOMENA

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1 IRG-1 SPIN-ORBIT COUPLING IN CORRELATED MATERIALS: SEARCH FOR NOVEL PHASES AND PHENOMENA Co-leads: N. Trivedi & P. M. Woodward 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 1

2 Spin orbit coupling Big Science Drivers for IRG-1 Topological Heavy Band Insulators Fermions 6s/6p Our focus: 5f/6f 4d/5d materials High T Metals & c Superconductors Band Insulators 3d Coulomb interactions = Band width 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 2

3 SOC Prediction experiment Hasan & Kane, RMP (2010) Qi & Zhang, RMP (2010) Big Science Drivers for IRG-1 Topological Band Insulators 6s/6p Metals & Band Insulators 4d/5d materials Interactions Heavy Fermions 5f/6f High T c Superconductors 3d Problem still unsolved after 25 years Gapless surface states protected by topology and symmetry silicon Why is band theory inadequate for large U/W? Electrons interact strong correlations many body problem Movement of one electron requires adjustment of all electrons IRG-1 3

4 SOC 4d/5d materials: The next frontier Topological Band Insulators 6s/6p Metals & Band Insulators Interactions 4d/5d materials Heavy Fermions 5f/6f High T c Superconductors 3d comparable energy scales New phases and new phenomena 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 4

5 SOC Why is topology important? Robust dissipationless current Spin-momentum locking spin filters Precise quantization 1 part in 10 9 in QHE What will 4d/5d oxides enable that is not achievable from other materials Topological Band Insulators 6s/6p Metals & Band Insulators Interactions 4d/5d materials (1) Topology + magnetism (1) Magnetoelectric response (3) Tunable room temperature magnetic heterostructures Fault tolerant spin based quantum computing Heavy Fermions 5f/6f High T c Superconductors 3d Why are Coulomb interactions important? Emergent phases Magnetism Data storage Generators High T c SC Transmission cables Wind turbines IRG-1 5

6 U/W Charge Orbital L Interplay of Spin-Orbit coupling & Correlations Spin S Mott Insulator Lattice Strain 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 6

7 4d/5d materials, bandwidth & interactions big 3d U Mo Tc Ru Rh 4d Cr Mn Fe Co small l Beyond 5d 5 Iridates Examples of electron count small 5d W Re Os Ir big Tuning correlations U & SOC l Perovskite Double Perovskite Pyrochlore Using structure & strain to tune orbital degeneracy & bandwidth W 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 7

8 M ( B /f.u.) Goals of IRG-1: 4d/5d materials Lay Foundations and Establish New Paradigms Topological phases Discovery Novel magnetism Understanding Tunable magnetic heterostructures -1 H film Control H (T) 1 0 H film CREATE: New magnetic materials: 4d and 5d oxides New principles: SOC + U New tunable heterostructures 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 8

9 Our Expertise Yang (Physics) Woodward co-lead (Chemistry) Trivedi co-lead (Physics) McComb (Materials Science) Windl (Materials Science) Randeria (Physics) Yan (Materials Science, Tennessee) Kaminski (Physics, Iowa State) Over 50 joint publications 8 with over 200 citations Valdes-Aguilar (Physics) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 9

10 Intensity (c/s) LSAT(002) Design & Synthesis of New Materials Woodward Materials are key Single Crystal Growth Yan + + Epitaxial Films Yang Proven experience with 5d oxides, including Os Vapor Transport Flux Growth High pressure floating zone Off-axis sputtering High quality and uniformity Stoichiometric & chemically ordered complex oxides Sr 2 CoOsO Sr 2 CrReO 6 /LSAT(001) t = 90 nm 10 3 Grown 10 new compounds with Ru or Os Sr 2 CoOsO 6 First single crystal 10 1 SCRO (004) (deg) Prominent Laue oscillations on strained films IRG-1 10

11 Intensity (c/s) LSAT(002) Design & Synthesis of New Materials Woodward Proven experience with 5d oxides, including Os Sr 2 CoOsO 6 Materials are key Single Crystal Growth Yan + + Vapor Transport Flux Growth High pressure floating zone 10 5 Sr 2 CrReO 6 /LSAT(001) t = 90 nm Epitaxial Films Yang crisis in the US about availability of high quality samples Off-axis sputtering High quality and uniformity Stoichiometric & chemically ordered complex oxides concerns about competitiveness and exploitation of new materials 10 3 Grown 10 new compounds with Ru or Os Sr 2 CoOsO 6 First single crystal 10 1 SCRO (004) (deg) Prominent Laue oscillations on strained films IRG-1 11

12 Theory: Insights Predictions Guide Experiments Experiments New materials Characterization DFT Bands Model Theory beyond DFT Strong interactions + Disorder + T 0 Effective field theory: Randeria Quantum Monte Carlo simulations: Trivedi Topological invariants Exact diagonalization Windl Finite temperature magnetic properties Raising Tc Doping and disorder PREDICTIONS ARPES and Optical conductivity Finite temperature band structure IRG-1 12

13 M ( B /f.u.) Grand challenges requiring a team effort Topological phases Novel magnetism Tunable magnetic heterostructures H film H film H (T) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 13

14 Bulk Dirac dispersion What is a Weyl semi-metal? Surface Fermi Arcs 3D analog of graphene; Weyl point robust Smoking gun Not observed yet! Broken time reversal symmetry or inversion symmetry Unusual magneto-electric effects pyrochlore lattice Wan, Turner, Vishwanath, Savrasov PRB 83, (2011) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 14

15 Weyl semi-metal in Pyrochlore Iridates Theory Prediction for A 2 Ir 2 O 7 Witczak-Krempa, Chen, Kim & Balents, Ann. Rev. Cond. Mat. Phys. 5, 57 (2014) Bulk A 2 Ir 2 O 7 Wan, Turner, Vishwanath, Savrasov PRB 83, (2011) Our Strategy: Epitaxial films of Pyrochlore Iridates Tuning with both rare-earth `A and strain 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 15

16 Intensity (c/s) (111) (333) (222) YSZ(111) (444) YSZ(222) Scanning transmission electron microscopy (STEM) First epitaxial film of any rare-earth iridate pyrochlore (McComb) Nd 2 Ir 2 O 7 : ideally placed for observing Weyl semi-metal Eu 2 Ir 2 O 7 : Eu is non-magnetic; all magnetism from Ir (c) Nd 2 Ir 2 O 7 film (deg) Growth and XRD (Yang) IRG-1 16

17 Advanced Spectroscopic capabilities to probe topological states like Weyl semi-metal ARPES: FERMI ARCS THz: KERR ROTATION NEUTRONS: 10 T 5K Kondo,... & Kaminski, PRL 111, (2013) First ARPES observation of Fermi Arcs in cuprates: Norman, Ding, Randeria et. al, Nature 392, 157 (1998) ~ 1000 citations colossal Kerr rotation! Valdés Aguilar et. al, PRL 108, (2012). Dynamical spin fluctuations Dunsiger, Yan, Woodward Clancy, Ruff, Dunsiger et. al, PRB 79, IRG-1 17

18 M ( B /f.u.) Grand challenges requiring a team effort Topological phases Novel magnetism Tunable magnetic heterostructures H film H film H (T) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 18

19 Novel Magnetism & Exchange Pathways Magnetic structure Neutron scattering (powder samples) Questions Sr 2 CoOsO 6 Os spins order at T N1 =110 K Co spins order at T N2 =70 K Coupling constants (DFT) J 1 eff = 1.3 mev J 2 eff = 47 mev J 3 eff = +20 mev J 4 eff = 13 mev Why do Goodenough-Kanamori rules fail? Why are longer range J 2 and J 3 so large? Why do Os and Co order independently? Proposed: Single xtals, other 3d/5d compounds Inelastic neutron scattering, XMCD Derive Hamiltonian w/ SOC anisotropic directional magnetism; Competing, frustrated states Morrow, Mishra, Restrepo, Ball, Windl, Wurmehl, Stockert, Büchner, & Woodward, JACS 135, (2013) IRG-1 19

20 Novel Magnetism & Quantum Phase Transitions 5d 2 Cd 2 Re 2 O 7 single xtal 2-3mm Superconductor T c = 1 K 5d 3 Cd 2 Os 2 O 7 single xtal < 0.2 mm Slater insulator T N = 227 K 5d 4 Y 2 Os 2 O 7 polycrystal Orbitally entangled ferromagnet 5d 5 RE 2 Ir 2 O 7 thin film Weyl semimetal predicted Cd 2 Re (2 x) Os (x) O 7 Proposed: Metal-insulator transition AF-paramagnet transition Role of SOC Tools: synthesis, xtal growth, THz, ARPES, neutrons, theory Prediction of novel magnetic d 4 Insulator (Resonant X-ray scattering) Meetei, Cole, Randeria, Trivedi, arxiv: IRG-1 20

21 M ( B /f.u.) Grand challenges requiring a team effort Topological phases Novel magnetism Tunable magnetic heterostructures H film H film H (T) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 21

22 M ( B /f.u.) M ( B /f.u.) Magnetic materials for oxide heterostructures Oxide epitaxy Hauser,, Woodward & Yang, PRB (2011) & PRB (2012); Sr 2 CrReO 6 XMCD: Hauser,, Windl,, Woodward & Yang, PRB (2014) SFMO anisotropy: Du,, Yang & Hammel, PRL (2013) High Tc and Exquisite strain tunable magnetocrystalline anisotropy ~ 10s of Tesla 1 0 SCRO/LSAT H film 1 SCRO/SCNO/LSAT +2.5% -1.0% H film H film -0.5 H film T = 300 K -1 T = 300 K H (T) Strain tuning H (T) Strain engineering on piezoelectric substrates Room temperature magnetism Itinerant Localized 3d/5d magnets Sr 2 CrOsO 6 (3d 3-5d 3 ) Ferrimagnet T C =720K Meetei, Erten, Randeria, Trivedi, & Woodward, PRL 110, (2013); Osmates LDA + DMFT: Meetei, Mravlje, Biermann, Georges, Randeria & Trivedi (preprint) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 22

23 M ( B /f.u.) IRG-1: Correlations + SOC in 4d & 5d materials: Why is our discovery program important? Topological phases Discovery Novel magnetism Understanding ARPES THz Beyond d 5 Iridates New Paradigms Tunable magnetic heterostructures Control H film H film H (T) Piezoelectric control of magnetism 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 23