gw study of half-metals and semiconductors

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