NiO - hole doping and bandstructure of charge transfer insulator

NiO NiO - hole doping and- hole doping andbandstructure bandstructure of chargeof charge

transfer insulatortransfer insulatorJan Jan KuneKunešš

Institute for Physics, Uni. AugsburgInstitute for Physics, Uni. Augsburg

Collaboration:Collaboration:V. I. V. I. AnisimovAnisimovS. L. S. L. SkornyakovSkornyakovA. V.A. V. Lukoyanov LukoyanovD. D. VollhardtVollhardt

OutlineOutline

• NiO - charge transfer insulator

• Theory so far

• Single particle spectra (PES, BIS)

• Hole doping LixNi1-xO• Bandstructure A(k,ω) (ARPES)

• Conclusions

• Single out an atom from the lattice• Replace the rest of the lattice by an effective medium• Time resolved treatment of local electronic interactions

Dynamical Mean-Field Theory (DMFT)Dynamical Mean-Field Theory (DMFT)

Physics Today (March 2004) Kotliar, Vollhardt

NiO NiO - so far- so far

NiO NiO - - BunseniteBunsenite

• rock-salt structure (Tm= 2261 K) bulk modulus: 209 GPa (CoO 194, MnO 148, diamond 462, Li 11)

• type II AFM (TN= 532 K)

• charge gap: 3.7 eV

• Formal valency: Ni2+: d8s0 O2-: p6

• U ~ 9 eV

Transition metal oxides: ZSA schemeTransition metal oxides: ZSA scheme

Δ

U

UHBUHB

O-p

LHB

Δ

U

UHB

O-p

LHB

Mott-Hubbard type (Ti-O, V-O) charge-transfer type (Ni-O,Cu-O)

O - 2p

Transition metal - 3d

NiONiO - - photoemissionphotoemissionEastman & Freeouf, PRL 34, 395 (1974):

1253 eV

30 eV

40 eV

78 eV

20 eV

d-states

multielectron satellite

p-states

• resonant d-peak at the top ofvalence band• distribution of spectral weightbetween LHB and resonantpeak• p-band between LHB andresonant peak

NiO NiO - LDA+U- LDA+UAnisimov et al., PRB 44, 943 (1991)

• long-range magnetic order

• ms ~ 2 µB (2 Eg holes)

• gap ~ 4 eV

• all d-spectral weight in LHB

LDA + orbitally dependent potential-> mean-field solution of Hubbard model

NiO NiO - Cluster results- Cluster resultsFujimori et al. PRB 29, 5225 (1984)

Exact diagonalization on [NiO6]10-

molecule with local Coulomb interaction

• model (~ 10 parameters)

• correct groundstate ms, gap

• correct d-weight distribution

• no dispersion (ARPES)

• not applicable to metals (doping, metal-insulator transition)

DMFT (QMC) - full p-dDMFT (QMC) - full p-dhybridizationhybridization

Part I: PhotoemissionPart I: Photoemission

NiO NiO - DMFT (QMC)- DMFT (QMC)

* Sawatzky & Allen, PRL 53, 2339 (1984)

120 eV

66 eV O-p

Ni-d

Theory:

Experiment*: Converged LDA Hamiltonianused as input for DMFT

QMC impurity solver

T = 1160 K

NiO NiO - DMFT (QMC)- DMFT (QMC)

* Sawatzky & Allen, PRL 53, 2339 (1984)

120 eV

66 eV O-p

Ni-d

Theory:

Experiment*: Converged LDA Hamiltonianused as input for DMFT

QMC impurity solver

T = 1160 K

DMFT (QMC) !

Orbital resolved spectral densities - DMFTOrbital resolved spectral densities - DMFT

LDA DOS

More experiment: XES/XASMore experiment: XES/XAS

courtesy of Prof. Ernst Kurmaev:


Part II: Hole dopingPart II: Hole doping

Hole doping of Hole doping of NiONiO

nnhh=0.6=0.6

1.45

1.61

1.85

ms

0.800.980.531.2

0.890.990.530.6

0.971.000.550.0

npnt2gnegnh

Orbital occupations:

Hole doping of Hole doping of NiONiO

nnhh=0.6=0.6

1.45

1.61

1.85

ms

0.800.980.531.2

0.890.990.530.6

0.971.000.550.0

npnt2gnegnh

Orbital occupations:

Holes reside on O - sites !

Experimental realization LiExperimental realization LixxNiNi1-x1-xOO

van Elp et al. PRB 45, 1612 (1992)

Li0.4Ni0.6O:nh=x/1-x

Experimental realization LiExperimental realization LixxNiNi1-x1-xOO

van Elp et al. PRB 45, 1612 (1992)

Li0.4Ni0.6O:nh=x/1-x

Spectral weight transfer


Part III: ARPESPart III: ARPES

NiONiO: k-resolved spectral functions: k-resolved spectral functions

O-p

Ni-Eg

Ni-T2g

NiO NiO : angle-resolved photoemission: angle-resolved photoemissionShen et al. PRB 44, 3604 (1991)

NiO NiO : angle-resolved photoemission: angle-resolved photoemissionShen et al. PRB 44, 3604 (1991)


O-p

Ni-Eg

Ni-T2g

NiONiO: Zhang-Rice bands: Zhang-Rice bands

• localized (k-independent) d-contribution

• strongly k-dependent p-contribution

ConslusionsConslusions

Anonymous referee: ‘…, all the DMFT community (excludingKunes and co-authors) are realizing this fact and simply do notencroach upon charge-transfer systems.’

LDA+DMFT can treat charge-transfer systems and does a verygood job for NiO.

- combination of dynamic correlations and p-d hybridization iscrucial -> Zhang-Rice bands at the top of the valence manifold anddistribution of spectral weight between ZR and LH bands

- ARPES is characterized by non-trivial combination ofdispersive and incoherent features, the ZR bands exhibit strong

k-dependence of the p-spectral weight (extensively discussed onmodels)

- NiO is charge-tranfer system <- doped holes sit on O sites

Lessons/questions :Lessons/questions :

• Filled unhybridized bands may exhibit pronounced correlationeffects

• Bandstructure intuition fails when it comes doping correlatedsystems (NiO: p-holes vs d-peak at µ, closing of the gap by doping

-different from the single-band Hubbard model)

• Ergodicity of QMC sampling is an issue in multi-orbital insulators

• How do we recognize a local moment system? Do we have tocalculate χ(0) vs T?

Future: Massive application to charge-transfer systems.

Full Coulomb interaction perturbative expansions (CTQMC).

Lower temperatures teperature dependent local moment transitions.





NiONiO: local moment dynamics: local moment dynamics

Simple p-d moleculeSimple p-d molecule

εd+U

εp

εd

e-

initial state final state

Documents

NiO - hole doping and bandstructure of charge transfer insulator