Spin splitting generated in a Y-shaped semiconductor nanostructure with a quantum point contact

Abstract

A proposal of a spin separator based on the spin Zeeman effect in Y-shaped nanostructure with a quantum point contact is presented. Our calculations show that the appropriate tuning of the quantum point contact potential and the external magnetic field leads to the spin separation of the current: electrons with opposite spins flow through the different output branches. We demonstrate that this effect is robust against the scattering on impurities. The proposed device can also operate as a spin detector, in which -depending on the electron spin -the current flows through one of the output branches.PACS numbers: 72.25.Dc A design of a controllable source of spin-polarized electrons and an efficient injection of the spin-polarized current into a semiconductor is a basic requirement for a fabrication of novel spintronic devices. The original idea of the spin transistor 1 was assumed that spin-polarized charges are injected into semiconductor channel from the ferromagnetic contact. However, due to the conductivity mismatch between the ferromagnetic and semiconductor materials, the efficiency of the spin injection at ferromagnet/semiconductor interface is rather low -experimentally reported at the level of a few percent. [2][3][4] The low spin-injection rate results in the low signal in the experimental realization of the spin transistor. 5 In order to overcome the conductivity mismatch, the spinpolarized current is injected into the semiconductor using the magnetic semiconductors. 6,7 In the experiments with the magnetic-semiconductor/semiconductor interface, the spin polarization rate reaches the value as high as 90 %. 8-10 Moreover, the use of magnetic semiconductors in resonant tunneling structures allows to construct the spin filter, in which the polarization of the current can be changed from fully spin-down to fully spin-up polarized by the bias voltage. 11,12 In our recent paper, 13 we have studied the spin filter effect in the resonant tunneling diode based on ferromagnetic GaMnN and shown that the spin filter operation can be realized even at room temperature. Several alternative methods to achieve the spin-polarizing effect in semiconductor nanostructures have been recently demonstrated in nanowires with spin-orbit interaction, 14,15 quantum dots, 16 and carbon nanotubes. 17 Although all these devices allow to obtain the spin polarized current, they do not separate the current into the beams with opposite spin. This operation is more complicated and requires the application of the device with at least three terminals: one terminal acts as the input through which the unpolarized current is injected, and the other two terminals act as outputs, through which the spin polarized beams flow out of the device. The spin separation effect in the presence of the spin-orbit interaction has been theoretically predicted in the ballistic T-shaped 18 and Y-shaped 19,20 structures as well as quantum rings. 21 The spin-orbit interaction in-duced by the quantum point contact (QPC) has been recently applied to reproduce the St...

Coherent spin transport through helical edge states of topological insulator

“…The suggested method allows for 100% spin polarization and therefore has essential advantages over the existing approaches to spin filtering and spin transfer based on resonant tunneling diodes 20,21 , quantum dots 22,23 , Y junctions 24,25 , and Aharonov-Bohm (AB) interferometers based on conventional materials 26 . In all these structures, spin polarization achieved so far was sufficiently small.…”

Effect of the tilted magnetic field on the magnetosubbands and conductance in the bilayer quantum wire

“…This example show the advantage of bilayer quantum wire over e.g. Y-shaped nanostructures 24,25 in preparing partially spin polarized current. Bi-layer nanowire enables one to get partially spin polarized current not only for the lowest subband but also for those lying higher on energy scale giving thus larger conductances and currents.…”

Helical and topological phase detection based on nonlocal conductance measurements in a three terminal junction

“…where N i is the number of transverse modes in the lead i and T ee ij , T he ij are the normal (electron-electron) and Andreev (electron-hole) transmission amplitudes corresponding to the situation when the electron is injected into the lead j and flow out from the device as an electron or hole through the lead i. For a non-superconducting system, the formula (2) reduces to the standard Landuer-Büttiker formula for a three terminal device 48 with G ij = e 2 h T ee ij .…”