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
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
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
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
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
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
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
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 -6-4 -2 0 2 4 6 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
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
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 6 10 5 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) 45 45.5 46 46.5 47 2 (deg) Prominent Laue oscillations on strained films IRG-1 10
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) 45 45.5 46 46.5 47 2 (deg) Prominent Laue oscillations on strained films IRG-1 11
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
M ( B /f.u.) Grand challenges requiring a team effort Topological phases Novel magnetism Tunable magnetic heterostructures 1 0-1 H film H film -6-4 -2 0 2 4 6 H (T) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 13
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, 205101 (2011) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 14
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, 205101 (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
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 10 7 10 5 10 3 10 1 (c) Nd 2 Ir 2 O 7 film 10 20 30 40 50 60 70 2 (deg) Growth and XRD (Yang) IRG-1 16
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, 157003 (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, 087403 (2012). Dynamical spin fluctuations Dunsiger, Yan, Woodward Clancy, Ruff, Dunsiger et. al, PRB 79, 014408 2009 IRG-1 17
M ( B /f.u.) Grand challenges requiring a team effort Topological phases Novel magnetism Tunable magnetic heterostructures 1 0-1 H film H film -6-4 -2 0 2 4 6 H (T) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 18
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, 18824 (2013) IRG-1 19
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:1311.2823 IRG-1 20
M ( B /f.u.) Grand challenges requiring a team effort Topological phases Novel magnetism Tunable magnetic heterostructures 1 0-1 H film H film -6-4 -2 0 2 4 6 H (T) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 21
M ( B /f.u.) M ( B /f.u.) Magnetic materials for oxide heterostructures Oxide epitaxy 0.5-0.5-1 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% 0.5 0 H film H film -0.5 H film T = 300 K -1 T = 300 K -6-4 -2 0 2 4 6 H (T) Strain tuning -6-4 -2 0 2 4 6 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, 087203 (2013); Osmates LDA + DMFT: Meetei, Mravlje, Biermann, Georges, Randeria & Trivedi (preprint) 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 22
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 1 0-1 H film H film -6-4 -2 0 2 4 6 H (T) Piezoelectric control of magnetism 3 June 2014 Center for Emergent Materials an NSF MRSEC IRG-1 23