Spi DME meeting Nijmegen May 2007 Stefano Sanvito

Spi. DME meeting, Nijmegen, May 2007 Stefano Sanvito and Nadjib Baadji Computational Spintronics Group School of Physics and CRANN, Trinity College

People Dr. Nadjib Baadji (Uni. Strasbourg), April ‘ 07 Mr. Sankar Kesanakurthi (U. Hiderabad), April ‘ 07 Visits Sanvito to Hamburg (Feb. 2007)

u A simple model for transport u Ab initio transport theory u SP-STM for molecules u Salen on Cu u Outlook

m. L V 0 GL e GR m. R

m. L e GR V m. R GL V≠ 0 In equilibrium Out of equilibrium 2

m. L e GR V m. R GL V≠ 0 2|EF- |

e = e 0 + U (N - f (e - m 0 )) L L R R m. L e GR V m. R GL V≠ 0

E +e. V/2 F E -e. V/2 F E T(E)

I

H= HM+H 0 +…. H 1 HLM HRM H 1 R L H 0 H 0 H 0 HM (n) HM+SL (E)+SR(E)

Lead’s Self-energy A. R. Rocha and S. Sanvito, PRB 70, 094406 (2004) Molecule Green function Density Matrix Current

KS-DFT Hamiltonian We implemented NEGF in Siesta Ø Localized multiple-z Pseudo-atomic orbitals (non-orthogonal) Ø Optimized Pseudopotential Ø Super-cells with up to 2, 000 atoms D. Sánchez-Portal, P. Ordejón, E. Artacho, and J. M. Soler, Int. J. Quant. Chem. 65, 453 (1997)

http: //www. smeagol. tcd. ie/ Mailing list http: //lists. tchpc. tcd. ie/listinfo/smeagol-discuss A. R. Rocha et al. , Phys. Rev. B 73, 085414 (2006); Nature Materials 4, 335 (2005)

Problems with molecular transport Ni point contacts C. Toher et al. , PRL 95, 146402 (2005) A. R. Rocha et al. , cond-mat/0701512 Fe/Mg. O TMR junction I. Rungger et al Spin Torque M. Stamenova et al. , in preparation DNA transport Molecular Spin valves A. R. Rocha et al. , in preparation Nature Mat. 4, 335 (2005)

80 n. A Au on Au 40 n. A V=250 m. V d=0. 4 nm 0 n. A 100 n. A Ni on Ni 50 n. A V=250 m. V d=0. 4 nm 0 n. A

20% 10% -10% I to tip 0% -30% -40% -30% I I P= I +I -55% -45% I from tip -70% -60% 500 m. V -250 m. V -500 m. V

Does the GMR mirror the polarization ? 10% -10% P= I I I +I -30% 250 m. V -10% -15% -20% I P I AP R= I AP

20% 500 m. V 10% 250 m. V -45% -250 m. V -50% -500 m. V

V=0

TIP M+S V=0

S S tip V

TIP M+S V=0

TIP M+S V=400 m. V Current to the tip

TIP M+S V=0

TIP M+S V=-400 m. V Current to the S+M

ØDirect calculations of the tunneling currents are possible and include: ü Electronic Structure of the tip ü Tip to sample interaction ü Charging of the moleculae ü Accurate determination of the spin-polarization ü Non-collinear spin ü Spin-orbit Ø Some prospects of investigating the bonding of molecules on magnetic surfaces

Molecule C 2 C 3 C 1 N, N'-BIS(SALICYLIDENE)ETHYLENEDIAMINO-TM Where TM could be : Cu, Zn, Ni or Co

Small DOS (arb. units) Big E (e. V) Comparison between the DOS of the Salen molecule and the hypothetical small molecule

Big Small E (e. V)

Cu-salen on Cu(001) Cu-salen on Cu(111) DOS (arb. units) Molecule on Cu surfaces (un-relaxed) E (e. V)

Relaxation on Cu(001) surface Unrelaxed structure Relaxed structure

DOS for different TM-salen DOS (arb. units) Cu E (e. V) 4 s 13 d 10

DOS (arb. units) Zn E (e. V) 4 s 23 d 10

DOS (arb. units) Co E (e. V) 4 s 23 d 7

DOS (arb. units) Ni 4 s 23 d 8 E (e. V)

Simulation STM images Free Cu-Salen EF-0. 2 e. V < EF EF < EF +0. 2 e. V I molecule to tip I tip to molecule

Constant current STM images Cu-Salen un-relaxed EF-0. 2 e. V < EF EF < EF +0. 2 e. V I molecule to tip I tip to molecule

Cu (a) (b) Zn (c) (d) EF-0. 2 e. V < EF EF < EF +0. 2 e. V I molecule to tip I tip to molecule

ØThis is very much work in progress ü First find the right atomic configuration ü Then simulate the current ü Compare the images for different TM ü Hopefully they will compare with experiments

integral of the DOS near Ef (pos. & neg. bias Cu DOS in free mole. and in mole. on Cu (001) L-resolved DOS for Cu atom in L-resolved DOS for Zn atom in t