Stefano Sanvito Computational Spintronics Group Physics Department, Trinity College Dublin CCTN’05, Göteborg 2005

Aknowledgements  J. Ferrer (Oviedo)  V. M. Garcia Suarez (Oviedo)  C.J. Lambert (Lancaster)  S. Bailey (Lancaster)  Science Foundation of Ireland  Enterprise Ireland  Alexandre Reily Rocha The Smeagol partners

Smeagol implements the NEGF method in DFT  Localized multiple-  Pseudo-atomic orbitals  Optimized Pseudopotential  Ceperley-Alder Exchange correlation  Large k-point sampling  Super-cells with up to 1,000-10,000 atoms D. Sánchez-Portal, P. Ordejón, E. Artacho, and J.M. Soler, Int. J. Quant. Chem. 65, 453 (1997) In particular we use SIESTA

Scattering Region Right Lead Left Lead  L =  F +V/2  R =  F -V/2 H s [n] f(  L )f(  R ) H0H0 H0H0 H0H0 H0H0 H0H0 H0H0 H0H0 H0H0 H0H0 H1H1 H1H1 H2H2 H2H2 H3H3 H3H3 H4H4 H4H4 LL RR

H= H s +H 0 +H 0 +H 0 +…. Hermitian problem for an open infinite system Non-hermitian problem for finite system H s +  L +  R

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

Total Hamiltonian Schrödinger equation Green Function Analytic form from Green equation and continuity Surface GF Use of boundary conditions S. Sanvito et al., Phys. Rev. B 59, (1999)

d orbitals fairly localized: no coupling between unit cells H 1 is close to singular Unitary Transformation  Highlights uncoupled states between principal layers  States are eliminated and couplings are renormalized  Numerically Stable We can solve for very complicated leads and the size of the system might be drastically downfolded!!! A. R. Rocha et al., in preparation

 It converges !! It can use leads with complicated electronic structure  It is spin-polarized  Both finite and periodic systems  Parallel in real space, k and E  It is non-collinear  Now LDA+SIC and LDA+U

Molecular Spin valves Nature Materials 4, 335 (2005) Fe/MgO TMR junction In preparation DNA transport In preparation H 2 molecular junction V. Garcia-Suarez, PRB in press Pt point contacts V. Garcia-Suarez, PRL in press

Experimental Results by Petta et al., PRL, 93, (2004) A. R. Rocha et al, Nature Materials 4, 335 (2005)

R= I P I AP I

 Smeagol is a powerful tool to study spin-transport at the nanoscale.  In Ni/Molecule/Ni the I-V presents a non-trivial behaviour and the GMR is strongly BIAS dependent  For pure tunneling GMR given by DOS at the contact  Prospects for large GMR devices

 LDA+SIC and LDA+U: now  Current induced forces: end 2005  Inelastic effects (phonons): mid 2006  Free distribution: September 2005  Spin-orbit coupling: end 2005  Multi-terminal: mid 2006