Shuttling of spin polarized electrons in molecular transistors

Shuttling of electrons in single-molecule transistors with magnetic leads in the presence of an external magnetic field is considered theoretically. For a current of partially spin-polarized electrons a shuttle instability is predicted to occur for a finite interval of external magnetic field strengths as shown in the figure, where the upper critical magnetic field (upper set of curves) and lower critical field (lower set of curves) for the shuttle transport regime are plotted as a function of the normalized tunneling rate Γ/ℏ ω of majority spin electrons for different values of spin polarization η. The solid curves were plotted for η = 1 [100% spin polarization, here the lower curve coincides with the x-axis], the dashed curves were plotted for η = 0 :8, and the short-dashed curves for η = 0 :3. The shuttle regime corresponds to the area between the lower and upper critical fields (dark region for the case of η = 0 :8), while outside this area one is in the vibronic regime. The feasibility of detecting magnetic shuttling in a C60-based molecular transistor with magnetic (Ni) electrodes is discussed [Pasupathy et al., Science 306 (2004) 86]. 58