GW Study of Half-metals and Semiconductors

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Presentation transcript:

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

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

Basic Idea EF ↑ ↓ I↑ too simple...

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

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).

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.

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)

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

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

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

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

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

Next Step GW...

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