Interplay of vibration and Coulomb effects in transport of spin-polarized electrons in a single-molecule transistor

Abstract

Tunnel transport of interacting spin-polarized electrons through a single-level vibrating quantum dot in external magnetic field is studied. By using density matrix method, the current-voltage characteristics and the dependence of conductance on temperature of a single-electron transistor were calculated. We found that a lifting of Coulomb blockade in external magnetic field happens in stages. The Franck-Condon steps associated with inelastic electron tunneling in our case are doubled due to contribution of two Zeeman-split levels in electron transport. The doubling of steps can be also observed in the presence of Coulomb interaction. For strong electron-vibron interaction the temperature dependence of conductance is shown to be non-monotonic and anomalous growth of conductance maximum weakly depends both on the Coulomb strength and the external magnetic field.

Thermoelectric Effects in Tunneling of Spin-Polarized Electrons in a Molecular Transistor

“…In [49], the previous paper of the author of this paper with coauthors, was demonstrated that the number of Franck-Condon steps in the current-voltage characteristics of spintronic molecular transistor is doubled due to the Zeeman splitting. Furthermore, strong Coulomb correlations lead to the appearance of a region without steps.…”

“…The Hamiltonian of the system after two unitary transformations: i) the rotation of axes and ii) Lang-Firsov transformation (the description of calculation process has been provided in detail in Ref. [49]) takes the form of a sum of four terms: H l , which remains the same, H d , which now reads…”

“…The charge current at low temperatures [49] has a form of step-like function, where each current jump is a manifestation of the opening of a new inelastic channel -tunneling with an emission of vibron.…”

“…Moreover, it has been predicted in [20] (see also [24], [49]), that in molecular transistor temperature dependence of differential electric conductance at intermediate temperatures, T ≃ ω (T is the average temperature, k B = 1 is the Boltzmann's constant, ω is the oscillation quantum), is anomalously non-monotonic. This can lead to unusual effects when studying thermoelectric phenomena.…”

Recent progress in single-molecule transistors: their designs, mechanisms and applications

“…At low temperatures, measurements with extremely high energy resolution have observed very fine gate-dependent physical effects, such as the Coulomb blockade, Kondo effect and electron-phonon coupling. [24][25][26] It can provide rich information on the molecule, including electronic transitions between energy levels, molecular vibrations and changes in spin states. Furthermore, some molecular-scale physical effects can be controlled by specially constructing single-molecule FETs, including quantum interference, spin, thermoelectric effects, superconductivity, and so on.…”