First-principles approach to ultrafast logic functionalization of magnetic molecules

Time: Thursday, October 25th, 15:10
Speaker: Wolfgang HÜBNER, Kaiserslautern

 Following the historic discovery of Beaurepaire et al. [1] five main time scales of ultrafast spin dynamics have been established: coherent electron-photon interaction, magnetic dephasing [2], electron-spin correlation, electron-phonon interaction, and spin-lattice interaction. The main focus of these demagnetization investigations was on extended ferromagnetic systems, corresponding to one point in the reciprocal space. Controlled switching additionally requires spin localization and thus two or more distinguishable active magnetic centers, thus leading to the investigation of antiferromagnets [3] or ferrimagnets [4].
Technological application, however, requires both spin localization and spin transfer. While reciprocal space approaches correspond to top-down patterning of nanostructures, we follow the bottom-up approach of molecular nanostructures. Pursuant to this approach, we use quantum chemical many-body methods to describe the electronic structure and ultrafast spin dynamics of various molecular nanostructures.
 In this way we are able to establish the following logic functionalities on small magnetic molecules: ERASE functionality, which can be realized in two-center molecules with chirp [5] or by exploiting quantum interference [6], OR gate in molecules with three active magnetic centers in the presence of an external actively participating magnetic field [7], and OR gate in in molecules with four active magnetic centers, and no active participation of the field. Exploiting quantum interference effects in four-center molecules we can also achieve spin bifurcation and merging [8]. Furthermore, we propose a cyclic SHIFT register (Fig. 1) using three active centers of a recently synthesized four-center molecule [9]. Quantum interference effects even allow us to implement non-Boolean logic functionalities in the very same molecules. Finally, we discuss over which distances spin can be transferred by femtosecond laser pulses.

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