Spin inelastic currents in molecular ring junctions

Within a simple model, we discuss spin inelastic currents in molecular ring junctions. We generalize considerations of the spin-flip inelastic electron tunneling spectroscopy (IETS) to the case of multisite molecular system, and formulate a conserving approximation, which takes into account renormalization of elastic channel. We also extend recent studies of circular currents in molecular junctions beyond scattering theory formulation. We demonstrate control of the spin-flip IETS signal and discuss spin polarization of total and circular currents in a benzene ring junction.

Figure 1

A tight-binding model for current conduction through a molecular ring $M$ with a spin impurity $\vec{S}$ at its center coupled to metal leads $L$ and $R$ in a meta position (sites of ortho and para configurations are indicated in the figure). External uniform magnetic field $\vec{B}$ is applied perpendicular to the ring plane.

Figure 2

Inelastic transport in a meta-connected benzene ring molecular junction. Shown are (a) conductance $dI/dV$ ($I_L=I_R\equiv I$) vs bias for several magnetic field strengths (negative $B$ represents a field pointing into the plane of the ring) and (b) circular conductance $d{I}_C/dV$ vs bias at $B=-10$ T for several values of electron-spin exchange parameter $J$.

Figure 3

Elastic channel renormalization in a meta-connected benzene ring molecular junction. Shown is conductance $dI/dV$ ($I_L=I_R\equiv I$) vs bias (a) at $B=-10$ T for two different values of gate voltage: $V_g=0.486$ V (solid line, black) and $0.490$ V (dashed line, red); (b) at $V_g=0.488$ V for two different values of applied magnetic field: $B=-5$ T (solid line, black; left and bottom axes) and $-10$ T (dashed line, red; right and top axes).

Figure 4

Current-voltage characteristics of a meta-connected molecular ring junction. Shown are (a) terminal current $I_L=I_R\equiv I$, Eq. (22), and (b) circular current $I_c$, Eq. (21), at $B=-5$ T for spin-up (dashed line, red), spin-down (dash-dotted line, blue), total charge (solid line, black), and total spin (dash-double-dotted line, green) currents. The inset in (a) shows the spin resolved local density of states $D_{\sigma }\left(E\right)$, Eq. (24), at $V=1$ V (spin-up - dashed line, red, spin-down - dash-dotted line, blue)

Figure 5

Spin-polarized transport in the para (solid line, black), meta (dashed line, red), and ortho (dash-dotted line, blue) connected molecular ring junctions. Shown are: (a) Spin polarization $P$, Eq. (25), as a function of applied magnetic field for at resonant bias ($V=1$ V), and (b) spin filter efficiency ${\eta }_{\sigma }$, Eq. (25), as function of the molecule-contacts coupling strength. Insets in (a) show spin polarization for bias below ($V=0.8$ V, upper inset) and above ($V=1.2$ V, lower inset) the resonance.