CEMC ENTER FOR EMERGENT MATERIALS The Ohio...

The Ohio State University http://cem.osu.edu CEM CENTER FOR EMERGENT MATERIALS

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


Big Science Drivers for IRG-1

Coulomb interactions

Metals & Band Insulators

Topological Band Insulators 6s/6p

Heavy Fermions

5f/6f

High Tc Superconductors

3d Spin

orb

it c

oupl

ing Our focus: 4d/5d materials

= Band width 3 June 2014 Center for Emergent Materials—an NSF MRSEC IRG-1 2


Big Science Drivers for IRG-1

Interactions



Heavy Fermions

5f/6f


3d

4d/5d materials

SOC

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

Prediction experiment Hasan & Kane, RMP (2010)

Qi & Zhang, RMP (2010) Problem still unsolved after

25 years

silicon

Gapless surface states protected by topology and symmetry

IRG-1 3


4d/5d materials: The next frontier

Interactions



Heavy Fermions

5f/6f


3d

4d/5d materials

comparable energy scales

New phases and new phenomena

SOC



What will 4d/5d oxides enable that is not achievable from other materials

SOC

Why are Coulomb

interactions important?

Emergent phases Magnetism

• Data storage • Generators

High Tc SC • Transmission cables • Wind turbines

(1) Topology + magnetism

(1) Magnetoelectric response

(3) Tunable room temperature magnetic heterostructures

Fault tolerant spin based quantum computing

Interactions



Heavy Fermions

5f/6f


3d

4d/5d materials

Why is topology important?

IRG-1 5

• Robust dissipationless current

• Spin-momentum locking spin filters

• Precise quantization 1 part in 109 in QHE


Interplay of Spin-Orbit coupling &

Correlations

Charge

Spin S Orbital L

U/W

Mott Insulator

Lattice Strain



4d/5d materials, bandwidth & interactions

Using structure & strain to tune

orbital degeneracy & bandwidth W

Tuning correlations U & SOC l

Examples of electron count l U Mo Tc Ru Rh

W Re Os Ir

Cr Mn Fe Co 3d

4d

5d

big

big small

small

Perovskite Double Perovskite Pyrochlore 3 June 2014 Center for Emergent Materials—an NSF MRSEC IRG-1 7

Beyond 5d5 Iridates


Goals of IRG-1: 4d/5d materials Lay Foundations and Establish New Paradigms

Topological phases

Discovery

Novel magnetism

Understanding

Tunable magnetic heterostructures

Control -6 -4 -2 0 2 4 6

-1

0

1

H (T)

M (

B/f

.u.)

H film

H || film

• New magnetic materials: 4d and 5d oxides

• New principles: SOC + U • New tunable

heterostructures

CREATE:



Woodward co-lead

(Chemistry)

Yan (Materials

Science, Tennessee)

Yang (Physics)

Kaminski (Physics,

Iowa State)

McComb (Materials Science)

Valdes-Aguilar (Physics)

Trivedi co-lead (Physics)

Randeria (Physics)

Windl (Materials Science)

Our Expertise

Over 50 joint publications 8 with over 200 citations



Materials are key Design & Synthesis of New

Materials Woodward

101

103

105

45 45.5 46 46.5 47

Inte

nsity

(c/

s)

2 (deg)

Sr2CrReO6/LSAT(001)

t = 90 nm

SCRO(004) LS

AT

(002

)

+ + Epitaxial

Films Yang

Sr2CoOsO6

First single crystal

Single Crystal Growth

Yan

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

Sr2CoOsO6

Grown 10 new compounds with Ru or Os

Prominent Laue oscillations on strained films

IRG-1 10


Materials are key Design & Synthesis of New

Materials Woodward

101

103

105

45 45.5 46 46.5 47

Inte

nsity

(c/

s)

2 (deg)

Sr2CrReO6/LSAT(001)

t = 90 nm

SCRO(004) LS

AT

(002

)

+ + Epitaxial

Films Yang

Sr2CoOsO6

First single crystal

Single Crystal Growth

Yan

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

Sr2CoOsO6

Grown 10 new compounds with Ru or Os

Prominent Laue oscillations on strained films

crisis in the US about availability of high

quality samples

concerns about competitiveness and exploitation of new

materials

IRG-1 11


Theory: Insights Predictions Guide Experiments

Experiments

New materials Characterization 𝑇 ≠ 0

Theory beyond DFT Strong interactions + Disorder + Effective field theory: Randeria Quantum Monte Carlo simulations: Trivedi Topological invariants Exact diagonalization

Model

Finite temperature magnetic properties

Raising Tc Doping and disorder

ARPES and Optical conductivity Finite temperature band structure

Windl

DFT Bands

PREDICTIONS

IRG-1 12


Grand challenges requiring a team effort

Topological phases

Novel magnetism


-6 -4 -2 0 2 4 6

-1

0

1

H (T)

M (

B/f

.u.)

H film

H || film



What is a Weyl semi-metal? Bulk Dirac dispersion

Unusual magneto-electric effects

Broken time reversal symmetry or inversion symmetry

Smoking gun Not

observed yet! 3D analog of graphene;

Weyl point robust

Wan, Turner, Vishwanath, Savrasov PRB 83, 205101 (2011)

Surface Fermi Arcs

pyrochlore lattice



Weyl semi-metal in Pyrochlore Iridates

Wan, Turner, Vishwanath, Savrasov PRB 83, 205101 (2011)

Theory Prediction for

A2Ir2O7

Our Strategy: Epitaxial films of

Pyrochlore Iridates Tuning with

both rare-earth `A’ and strain Witczak-Krempa, Chen, Kim & Balents,

Ann. Rev. Cond. Mat. Phys. 5, 57 (2014)

Bulk A2Ir2O7



Scanning transmission electron microscopy (STEM)

Growth and XRD

(Yang)

First epitaxial film of any rare-earth iridate pyrochlore

Nd2Ir2O7: ideally placed for observing Weyl semi-metal Eu2Ir2O7: Eu is non-magnetic; all magnetism from Ir

101

103

105

107

10 20 30 40 50 60 702 (deg)

(c) Nd2Ir

2O

7 film

(111

) (222

)

(333

)

(444

)

YS

Z(2

22)

YS

Z(1

11)

Inte

nsit

y (c

/s)

(McComb)

IRG-1 16


ARPES: FERMI ARCS THz: KERR ROTATION NEUTRONS:

Dynamical spin fluctuations

Dunsiger,

Yan, Woodward

colossal Kerr rotation!

Valdés Aguilar et. al, PRL 108, 087403 (2012).

Advanced Spectroscopic capabilities to probe topological states like Weyl semi-metal

Clancy, Ruff, Dunsiger et. al, PRB 79, 014408 2009

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

10 T 5K

IRG-1 17



Topological phases

Novel magnetism


-6 -4 -2 0 2 4 6

-1

0

1

H (T)

M (

B/f

.u.)

H film

H || film



Sr2CoOsO6 Os spins order at TN1=110 K Co spins order at TN2=70 K

Coupling constants (DFT) J1

eff = −1.3 meV

J2eff = −47 meV

J3eff = +20 meV

J4eff = −13 meV

Novel Magnetism & Exchange Pathways

Morrow, Mishra, Restrepo, Ball, Windl, Wurmehl, Stockert, Büchner, & Woodward, JACS 135, 18824 (2013)

Questions

Why do Goodenough-Kanamori rules fail?

Why are longer range J2 and J3 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

IRG-1 19

Magnetic structure Neutron scattering (powder samples)


Novel Magnetism & Quantum Phase Transitions

5d2 Cd2Re2O7

single xtal 2-3mm Superconductor

Tc = 1 K

Cd2Re(2−x)Os(x)O7

Proposed: • Metal-insulator transition • AF-paramagnet transition • Role of SOC • Tools: synthesis, xtal growth,

THz, ARPES, neutrons, theory

5d3 Cd2Os2O7

single xtal < 0.2 mm Slater insulator

TN = 227 K

5d4 Y2Os2O7 polycrystal

Orbitally entangled ferromagnet

5d5 RE2Ir2O7

thin film Weyl semimetal

Prediction of novel magnetic

d4 Insulator (Resonant X-ray

scattering)

Meetei, Cole, Randeria, Trivedi, arXiv:1311.2823

predicted

IRG-1 20



Topological phases

Novel magnetism


-6 -4 -2 0 2 4 6

-1

0

1

H (T)

M (

B/f

.u.)

H film

H || film



Magnetic materials for oxide heterostructures

3d/5d magnets Sr2CrOsO6(3d3-5d3)

Ferrimagnet TC=720K

Hauser, …, Woodward & Yang, PRB (2011) & PRB (2012); Sr2CrReO6 XMCD: Hauser, …, Windl, …, Woodward & Yang, PRB (2014) SFMO anisotropy: Du, …, Yang & Hammel, PRL (2013)

Meetei, Erten, Randeria, Trivedi, & Woodward, PRL 110, 087203 (2013); Osmates LDA + DMFT: Meetei, Mravlje, Biermann, Georges, Randeria & Trivedi (preprint)

Itinerant Localized

High Tc and Exquisite strain

tunable magneto-crystalline anisotropy

~ 10s of Tesla

Strain engineering on

piezoelectric substrates

-6 -4 -2 0 2 4 6

-1

-0.5

0

0.5

1

H (T)

T = 300 K

SCRO/LSAT

H film

H || filmM

(

B/f

.u.)

-6 -4 -2 0 2 4 6

-1

-0.5

0

0.5

1

H (T)

T = 300 K

M (

B/f

.u.)

SCRO/SCNO/LSAT

H film

H || film

+2.5% -1.0%

Strain tuning Room temperature magnetism


Oxide epitaxy


Topological phases

Discovery

Novel magnetism

Understanding


Control

IRG-1: Correlations + SOC in 4d & 5d materials: Why is our discovery program important?

Piezoelectric control of

magnetism

New Paradigms

-6 -4 -2 0 2 4 6

-1

0

1

H (T)

M (

B/f

.u.)

H film

H || film

ARPES

THz

Beyond d5 Iridates


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