Coherent Manipulation of Polarization in Mixed-Valence Compounds by Electric Pulse via Landau–Zener Transitions

Abstract

In this contribution, we predict and theoretically investigate the effects of the electric field pulse in mixed valence (MV) dimers. These systems exhibit bistability with a large internal dipole moment mediated by the itinerant electron trapped by the vibronic coupling. In this sense, they are similar to single molecular magnets (SMMs) that are bistable systems possessing large long-living magnetization and exhibiting Landau–Zener (LZ) transitions. We propose a scheme for a controllable LZ tunnelling in MV systems that provides also a possibility to control the dipole moment of a dimeric MV unit. It is supposed that the static electric field initially polarizes the system, and then the unit is subjected to a short electric pulse controlling the LZ transitions. The model includes the vibronic pseudo Jahn–Teller (JT) coupling in a MV dimeric system belonging to Class II in Robin and Day classification. We elucidate the main factors controlling coherent nonadiabatic LZ tunneling between the low-lying vibronic levels induced by a short pulse of the electric field. The transition probabilities and consequently polarization induced via the LZ transitions are shown to be dependent on both the time of the pulse and total spin of the cluster. We have suggested to employ the electric field pulse as a tool for the direct observation of the tunneling splitting through the coherent LZ transitions. The magnetic MV systems in which the double exchange is operative are shown to provide a possibility to control electric polarization through the spin-dependent LZ tunneling by applying an additional static magnetic field. The ability of MV systems to change electric polarization in a controllable manner seems to be significant for potential applications.