We theoretically propose an all-electrically controlled spin-current diode consisting of a quantum dot sandwiched between one normal electrode and one ferromagnetic electrode. By applying a spin bias VS across one electrode, the spin current distribution shows a rectification effect; that is, in the forward spin bias regime, a spin current can tunnel through the junction, while in the reverse bias regime, the current is tiny. Such asymmetry in the spin-current profile suggests diode-like behavior with respect to the spin bias. Moreover, the polarity direction of this spin-current diode can be manipulated and reversed by adjusting the gate voltage, which is much more feasible than the approach with traditional charge-current diodes. The present device can be realized by current technologies and has potential applications in spintronics or quantum information processing.

In this letter, we theoretically propose a spin diode and spin valve device controlled by all-electrical means, which is composed of a quantum dot coupled to a pair of nonmagnetic electrodes. When both electric charge bias and spin bias exist within the device, the I-V curves of this device exhibit an asymmetric distribution.More interestingly, if we apply an external magnetic field on the quantum dot,it can be observed significant high- and low-resistance state switching with respect to the magnetic field, which can function as a spin valve. This device is compatible with current technologies and has potential applications in spintronics.

Utilizing vector PFM (piezoresponse force microscopy) on high-density nanodot arrays, ferroelectric nanodots and domain structure in nanodot arrays were investigated in the current study. Accordingly, we identified four types of topological domain states based on the measurements of spontaneous polarization vectors vs writing results in nanodots. In addition to convergent and divergent domains with upward and downward polarization, double-center domains and triple-center domains were also identified. In addition, center domains could be reversibly switched under the electric field produced by the biased PFM tip, and their stability could be maintained by compensating the polarization charge with the accumulated charge. These stable topological domain states in discrete nanodots present an opportunity to further investigate their new properties in high-density memory devices.