gw study of half-metals and semiconductors
DESCRIPTION
Half-metal --- application DOS ↑ ↓ ↑ ↑ Half-metal EF ↓ ↓ Applications Spin valve --- MRAM Spin OLED (organic light emitting diode)TRANSCRIPT
GW Study of Half-metals and Semiconductors
Hiori Kino
Half-metal: application, fullpotential calculationSemiconductor: impurity problem
Half-metal --- application
•Spin valve --- MRAM•Spin OLED (organic light emitting diode)
DOS
EF
Half-metal ↑
↓
↑ ↓ ↑
↓
Applications
Basic Idea
EF
↑ ↓
EF
↑ ↓
I↑
I↑
too simple...
Spin valve --- MRAM
-30%
Xiong et al., Nature 427, 821 (2004).
e↑
Alq=8-hydroxyquinoline aluminium
Spin OLED (organic light emitting diode)
---Organic EL (electroluminescence)
e↑
h↑
h
semiconductor
S0 S1T1
L
L+1
luminescence phosphorescence
Organic semiconductor•small Z: small LS coupling•long spin life time
Change luminescence efficiency
=0%
h
E.g. Davis and Bussmann, JAP 93, 7358 (2003).
(slow)
||
La0.7Sr0.3MnO3, (La0.7Ba0.3MnO3,La0.7Ca0.3MnO3)
LaMnO3: collosal magnetoresistance oxidesa strongly correlated system(intrinsic ramdomness)
In theoriesLSDA: 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.
Experimental results
Non-zero DOS at EF = partially spin-polarizedAndreev 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-polarizedXPS, Park et al.resistivity, Zhao et al. (bulk)tunnel, Wei et al. (bulk)
For the Minority spin state
LDA
knVEknE LDAXCkn
LDAknkn |)(|
(use only the diagonal self-energy)
Bare Exchange and Correlated parts
(RPA, without vertex correction)
made of and
)(qv
LDAkn LDA
kn
+ +
LDAkn
LDAkn
LDAkn
LDAXCext rnv
rrrndrv
mp
))((
|'|)'('
2
2
GWA
+
GW method: first-principles (no parameter), correlation= RPA-level
L. Hedin, J. Phys. Condens. Matter 11,R489(1999)
i
LDAi n
E Ionization energy )()1( NENE
e.g. GW improves bandgaps
•LMTO-ASA•virtual crystal approx.
Mn eg Mn t2g
Mn eg
Mn t2g
La
MnO
Pm-3m
LSDA results of La0.7Sr0.3MnO3
Majority Mn eg <- Fermi levelMinority Mn t2g <- Fermi level
fp-LMTO calculation
La 4f
More accurate dispersion at higher energies
Majority spin
fp-LMTO
Minimum basis
O3s
O3p La7s
La6d Mn 5s
Mn 5p Mn4d
Double Hankel
La 5p(semicore)
Next Step
•GW...
Impurity level of semiconductors
acceptor
donor
LDA orbital energyquasiparticle energyunoccupied energy level: underestimated
GW
Si
Direct determination of acceptor and donor levels