GW Study of Halfmetals and Semiconductors Hiori Kino

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

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

Basic Idea I↑ ↑ ↓ EF I↑ too simple. . .

Spin valve --- MRAM e↑ 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 hn L+1 L phosphorescence hn (slow) S 0 T 1 S 1 h↑ e↑ semiconductor =0% Organic semiconductor • small Z: small L S coupling • long spin life time E. g. Davis and Bussmann, JAP 93, 7358 (2003).

La 0. 7 Sr 0. 3 Mn. O 3, (La 0. 7 Ba 0. 3 Mn. O 3, La 0. 7 Ca 0. 3 Mn. O 3) La. Mn. O 3: 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 La 0. 7 Sr 0. 3 Mn. O 3 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, R 489(1999)

LSDA results of La 0. 7 Sr 0. 3 Mn. O 3 • LMTO-ASA • virtual crystal approx. La O Mn Pm-3 m Mn eg Mn t 2 g Majority Mn eg <- Fermi level Minority Mn t 2 g <- Fermi level Mn eg Mn t 2 g

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

fp-LMTO Double Hankel O 3 s Minimum basis O 3 p La 5 p(semicore) La 7 s La 6 d Mn 5 s Mn 5 p Mn 4 d

Next Step • GW. . .

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