HDR : Ab initio study of electron transport and magnetism in nanostructures

Alexander Smogunov

Vendredi 25/11/2016, 10:00-12:00

My research interests are mainly focused on theoretical study and simulation of electron transport and magnetism in atomic-scale nanostructures such as atomic or molecular nanojunctions, single (magnetic) ad-atoms or molecules deposited on various substrates, and so on. The main tool in my studies is the *ab initio* electronic structure package Quantum-ESPRESSO (QE) based on the Density Functional Theory (DFT), which is used either directly or to extract some necessary parameters for further model simulations. I have developed, in particular, the quantum transport code PWCOND – which is a part of the QE package – for solving a quantum-mechanical scattering problem in atomic-scale systems with open boundary conditions such as, for example, atomic nanocontacts or magnetic tunnel junctions (MTJ).

I will review some of my most interesting studies accomplished with those methods and codes:

- Theoretical prediction of spontaneous formation of local magnetic moment in Platinum atomic chains and nanocontacts and its possible experimental detection by magneto-resistance measurements;
- Achieving fully spin-polarized electron currents across a special class of molecules bridging two ferromagnetic electrodes. The mechanism relies on orbital mismatch between molecule and electrode electronic states and allows, moreover, to quench completely the current by inverting the magnetization of one electrode with respect to another, resulting thus in infinite magneto-resistance ratio;
- Simulation of the Kondo physics (when a local spin moment is coupled to unpolarized conduction band and becomes fully screened at low temperatures) in realistic nanosystems using combined DFT+NRG (Numerical renormalization group) approach. The method is demonstrated on example of single Ni ad-atoms at Au nanocontacts. The symmetry of magnetic (singly occupied) Ni orbital will be shown to be crucial, affecting strongly the low temperature transport characteristics;
- Spin moment reorientation in Co films from in-plane to out-of-plane direction upon adsorption of C
_{60}molecules, as also reported experimentally. It results from a strong hybridization of specific Co states with C_{60}orbitals. The effect is known as perpendicular magnetic anisotropy (PMA), very important in the field of spintronics.

Contact : Alexander
SMOGUNOV