1. GW Study of Half-metals and Semiconductors
Hiori Kino
Half-metal: application, fullpotential calculation
Semiconductor: impurity problem

2. Half-metal --- application
DOS ↑ ↓ ↑ ↑
Half-metal EF ↓ ↓
Applications
Spin valve --- MRAM
Spin OLED (organic light emitting diode)

3. Basic Idea EF ↑ ↓ I↑
too simple...

4. Spin valve --- MRAM -30% e↑ Xiong et al., Nature 427, 821 (2004).
Alq=8-hydroxyquinoline aluminium
-30%
Xiong et al., Nature 427, 821 (2004).

5. Spin OLED (organic light emitting diode) ---Organic EL (electroluminescence)
Change luminescence efficiency
luminescence
phosphorescence hn hn
L+1
(slow) L T1 S0 S1 e↑ h↑
Organic semiconductor
small Z: small LS coupling
long spin life time
=0%
semiconductor
E.g. Davis and Bussmann, JAP 93, 7358 (2003).

6. La0.7Sr0.3MnO3, (La0.7Ba0.3MnO3,La0.7Ca0.3MnO3)
LaMnO3: collosal magnetoresistance oxides
a strongly correlated system
(intrinsic ramdomness)
In theories
LSDA: nonzero DOS at EF in minority spin component
In experiments, many experiments:
spin polarization: 35%-100%
In this study,
calculate La0.7Sr0.3MnO3 beyond LSDA.
estimate a band gap in the GW approximation.

7. Experimental results For the Minority spin state
Non-zero DOS at EF = partially spin-polarized
Andreev reflection, Soulen Jr. et al.,
tunnel junction, Lu et al., Worledge et al., Sun et al.,
residual resistivity, Nadgomy et al. (bulk)
Zero DOS at EF=fully spin-polarized
XPS, Park et al.
resistivity, Zhao et al. (bulk)
tunnel, Wei et al. (bulk)

8. GW method: first-principles (no parameter), correlation= RPA-level
LDA
GWA
(RPA, without vertex correction)
(use only the diagonal self-energy) + + +
Bare Exchange and Correlated parts
made of and

9. e.g. GW improves bandgaps
Ionization energy
L. Hedin, J. Phys. Condens. Matter 11,R489(1999)

10. LSDA results of La0.7Sr0.3MnO3
LMTO-ASA
virtual crystal approx. La O
Majority Mn eg <- Fermi level
Minority Mn t2g <- Fermi level Mn
Pm-3m
Mn eg
Mn eg
Mn t2g
Mn t2g

11. fp-LMTO calculation La 4f More accurate dispersion at higher energies
Majority spin
La 4f
More accurate dispersion
at higher energies

12. fp-LMTO Double Hankel O3s Minimum basis La7s O3p La 5p(semicore) La6d
Mn 5s
Mn 5p
Mn4d

13. Next Step
GW...

14. Impurity level of semiconductors
donor
acceptor Si
Direct determination of acceptor and donor levels GW
LDA orbital energyquasiparticle energy
unoccupied energy level: underestimated