High Conductance and Full Spin Polarized Current Transistor

We studied the transport properties of a device composed by a quantum dot, (QD), connected to the first site of a conventional metallic semi-chain and side connected to a spin-orbit interacting (SOI) nano-ribbon. The system is under the effect of an external applied potential, so that it operates in an out-of-equilibrium regime, studied within the context of the Green Function Keldysh formalism This permits to calculate the density of states that manifests a very clear strong spin dependence and the current circulating along the system. The implicit correlation of the spin orientation of the charge produced by the applied voltage explains the transport properties of the system. It is characterized by the emergency of a spin polarized electrical current in despite of its non-magnetic nature. The SOI in a 1D system defines a linear momentum dependent pseudo magnetic field whose spatial direction determines an axis along which the electronic spin is quantized as a good quantum number, necessary to determine the state of the system. Remarkably, the SOI and the broken time reversal symmetry produced by the external potential define an energy region accessible by states with only one spin and momentum directions, where the Fermi levels can be localized.
Manipulation of the conductor doping and the external applied voltage make it possible to obtain a device with maximum of a quantum of conductance that sustains a high and completely spin polarized current. The spin polarized current can be perfectly controlled by the gate potential at the QD. Due to the local character of the QD levels, the Coulomb interaction is an important ingredient to describe the system, enhancing the parameter region within which it can operate.
The effects of the intra-dot Coulomb interaction are analyzed within the context of the Hubbard III approximation (the alloy analogy) that provides an adequate understanding of the Coulomb blockade regime and the transport properties of these systems, above the Kondo temperature. Below this temperature and for small applied potentials, the Kondo regime permits to manipulate the properties of the device. These properties are studied using the slave boson formalism.
We show that the system possesses all the requirements necessary to operate as a totally spin polarized current transistor, which qualifies it as a potential important tool for spintronic applications.